JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Question Bank

done Biot-savart's Law and Amperes Law Total Questions - 126

• question_answer1)
  A length L of wire carries a steady current I. It is bent first to form a circular plane coil of one turn. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the centre caused by the same current is                       [NCERT 1980; AIIMS 1980; MP PMT 1995, 99]
  A)
             A quarter of its first value done clear
  B)
             Unaltered done clear
  C)
             Four times of its first value done clear
  D)
             A half of its first value done clear
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• question_answer2)
  A vertical straight conductor carries a current vertically upwards. A point P lies to the east of it at a small distance and another point Q lies to the west at the same distance. The magnetic field at P is                [MNR 1986; DPMT 2004]
  A)
             Greater than at Q done clear
  B)
             Same as at Q done clear
  C)
             Less than at Q done clear
  D)
             Greater or less than at Q depending upon the strength of the current done clear
  View Solution play_arrow

• question_answer3)
  If a copper rod carries a direct current, the magnetic field associated with the current will be [CPMT 1984]
  A)
             Only inside the rod done clear
  B)
             Only outside the rod done clear
  C)
             Both inside and outside the rod done clear
  D)
             Neither inside nor outside the rod done clear
  View Solution play_arrow

• question_answer4)
  If a long hollow copper pipe carries a direct current, the magnetic field associated with the current will be [CBSE PMT 1999; AFMC 1999; CPMT 1984, 2000; Pb. PET 2000; JIPMER 2002]
  A)
             Only inside the pipe done clear
  B)
             Only outside the pipe done clear
  C)
             Neither inside nor outside the pipe done clear
  D)
             Both inside and outside the pipe done clear
  View Solution play_arrow

• question_answer5)
  The magnetic field \[d\overrightarrow{B}\] due to a small current element \[d\overrightarrow{l\,}\] at a distance \[\overrightarrow{r\,}\]  and element carrying current i is, or            Vector form of Biot-savart's law is  [CBSE PMT 1996; MP PET 2002; MP PMT 2000]
  A)
             \[d\overrightarrow{B}=\frac{{{\mu }_{0}}}{4\pi }i\,\left( \frac{d\overrightarrow{l\,}\times \overrightarrow{r\,}}{r} \right)\]     done clear
  B)
             \[d\overrightarrow{B}=\frac{{{\mu }_{0}}}{4\pi }{{i}^{2}}\,\left( \frac{d\overrightarrow{l\,}\times \overrightarrow{r\,}}{r} \right)\] done clear
  C)
             \[d\overrightarrow{B}=\frac{{{\mu }_{0}}}{4\pi }{{i}^{2}}\,\left( \frac{d\overrightarrow{l\,}\times \overrightarrow{r\,}}{{{r}^{2}}} \right)\]                                  done clear
  D)
             \[d\overrightarrow{B}=\frac{{{\mu }_{0}}}{4\pi }i\,\left( \frac{d\overrightarrow{l\,}\times \overrightarrow{r\,}}{{{r}^{3}}} \right)\] done clear
  View Solution play_arrow

• question_answer6)
  A charge q coulomb moves in a circle at n revolutions per second and the radius of the circle is r metre. Then magnetic field at the centre of the circle is
  A)
             \[\frac{2\pi q}{nr}\times {{10}^{-7}}\] N/amp/metre            done clear
  B)
             \[\frac{2\pi q}{r}\times {{10}^{-7}}\] N/amp/metre done clear
  C)
             \[\frac{2\pi nq}{r}\times {{10}^{-7}}\]N/amp/metre done clear
  D)
             \[\frac{2\pi q}{r}\] N/amp/metre done clear
  View Solution play_arrow

• question_answer7)
  An infinitely long straight conductor is bent into the shape as shown in the figure. It carries a current of i ampere and the radius of the circular loop is r metre. Then the magnetic induction at its centre will be                              [MP PMT 1999]
  A)
             \[\frac{{{\mu }_{0}}}{4\pi }\frac{2i}{r}(\pi +1)\] done clear
  B)
              \[\frac{{{\mu }_{0}}}{4\pi }\frac{2i}{r}(\pi -1)\] done clear
  C)
             Zero done clear
  D)
             Infinite done clear
  View Solution play_arrow

• question_answer8)
  A current i ampere flows in a circular arc of wire whose radius is R, which subtend an angle \[3\pi /2\] radian at its centre. The magnetic induction B at the centre is
  A)
             \[\frac{{{\mu }_{0}}i}{R}\] done clear
  B)
             \[\frac{{{\mu }_{0}}i}{2R}\] done clear
  C)
             \[\frac{2{{\mu }_{0}}i}{R}\] done clear
  D)
             \[\frac{3{{\mu }_{0}}i}{8R}\] done clear
  View Solution play_arrow

• question_answer9)
  A current i ampere flows along the inner conductor of a coaxial cable and returns along the outer conductor of the cable, then the magnetic induction at any point outside the conductor at a distance r metre from the axis is
  A)
             \[\infty \]                               done clear
  B)
             Zero done clear
  C)
             \[\frac{{{\mu }_{0}}}{4\pi }\frac{2i}{r}\]                        done clear
  D)
             \[\frac{{{\mu }_{0}}}{4\pi }\frac{2\pi \,i}{r}\] done clear
  View Solution play_arrow

• question_answer10)
  A straight section PQ of a circuit lies along the X-axis from \[x=-\frac{a}{2}\] to \[x=\frac{a}{2}\] and carries a steady current i. The magnetic field due to the section PQ at a point X = + a  will be                                                         [MP PMT 1987]
  A)
             Proportional to a                 done clear
  B)
             Proportional to \[{{a}^{2}}\] done clear
  C)
             Proportional to \[1/a\]     done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer11)
  A helium nucleus makes a full rotation in a circle of radius 0.8 metre in two seconds. The value of the magnetic field B at the centre of the circle will be [CPMT 1988; KCET 1998; UPSEAT 2001]
  A)
             \[\frac{{{10}^{-19}}}{{{\mu }_{0}}}\]                               done clear
  B)
             \[{{10}^{-19}}{{\mu }_{0}}\] done clear
  C)
             \[2\times {{10}^{-10}}{{\mu }_{0}}\]                              done clear
  D)
             \[\frac{2\times {{10}^{-10}}}{{{\mu }_{0}}}\] done clear
  View Solution play_arrow

• question_answer12)
  A solenoid of 1.5 metre length and 4.0 cm diameter posses 10 turn per cm. A current of 5 ampere is flowing through it. The magnetic induction at axis inside the solenoid is [CPMT 1990]
  A)
             \[2\pi \times {{10}^{-3}}\,tesla\]                                      done clear
  B)
             \[2\pi \times {{10}^{-5}}\,Tesla\] done clear
  C)
             \[4\pi \times {{10}^{-2}}\,Gauss\]                                   done clear
  D)
             \[2\pi \times {{10}^{-5}}\,gauss\] done clear
  View Solution play_arrow

• question_answer13)
  The magnetic induction at a point P which is distant 4 cm from a long current carrying wire is \[{{10}^{-8}}\,Tesla\]. The field of induction at a distance 12 cm from the same current would be                    [CBSE PMT 1990; DPMT 2001]
  A)
             \[3.33\times {{10}^{-9}}\,Tesla\]                                      done clear
  B)
             \[1.11\times {{10}^{-4}}\,Tesla\] done clear
  C)
             \[3\times {{10}^{-3}}\,Tesla\]                                            done clear
  D)
             \[9\times {{10}^{-2}}\,Tesla\] done clear
  View Solution play_arrow

• question_answer14)
  The strength of the magnetic field at a point r near a long straight current carrying wire is B. The field at a distance \[\frac{r}{2}\] will be                                               [MP PMT 1990]
  A)
             \[\frac{B}{2}\]                      done clear
  B)
             \[\frac{B}{4}\] done clear
  C)
             2B   done clear
  D)
             4B done clear
  View Solution play_arrow

• question_answer15)
  Field at the centre of a circular coil of radius r, through which a current I flows is                                 [MP PMT 1993]
  A)
             Directly proportional to r done clear
  B)
             Inversely proportional to I done clear
  C)
             Directly proportional to I done clear
  D)
             Directly proportional to \[{{I}^{2}}\] done clear
  View Solution play_arrow

• question_answer16)
  A current of 0.1 A circulates around a coil of 100 turns and having a radius equal to 5 cm. The magnetic field set up at the centre of the coil is            \[({{\mu }_{0}}=4\pi \times {{10}^{-7}}\,weber/ampere-metre)\]                 [MP PMT 1993]
  A)
             \[4\pi \times {{10}^{-5}}\,tesla\]                                      done clear
  B)
             \[8\pi \times {{10}^{-5}}\,tesla\] done clear
  C)
             \[4\times {{10}^{-5}}\,tesla\] done clear
  D)
             \[2\times {{10}^{-5}}\,tesla\] done clear
  View Solution play_arrow

• question_answer17)
  The magnetic field B with in the solenoid having n turns per metre length and carrying a current of i ampere is given by              [MP PET 1993]
  A)
             \[\frac{{{\mu }_{0}}ni}{e}\]    done clear
  B)
             \[{{\mu }_{0}}ni\] done clear
  C)
             \[4\pi {{\mu }_{0}}ni\]      done clear
  D)
             ni done clear
  View Solution play_arrow

• question_answer18)
  The magnetic induction at the centre O in the figure shown is                     [IIT 1988; KCET 2002]
  A)
             \[\frac{{{\mu }_{0}}i}{4}\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\]             done clear
  B)
             \[\frac{{{\mu }_{0}}i}{4}\left( \frac{1}{{{R}_{1}}}+\frac{1}{{{R}_{2}}} \right)\] done clear
  C)
             \[\frac{{{\mu }_{0}}i}{4}({{R}_{1}}-{{R}_{2}})\]           done clear
  D)
             \[\frac{{{\mu }_{0}}i}{4}({{R}_{1}}+{{R}_{2}})\] done clear
  View Solution play_arrow

• question_answer19)
  Field inside a solenoid is                                         [MP PMT 1993]
  A)
             Directly proportional to its length done clear
  B)
             Directly proportional to current done clear
  C)
             Inversely proportional to total number of turns done clear
  D)
             Inversely proportional to current done clear
  View Solution play_arrow

• question_answer20)
  In the figure, shown the magnetic induction at the centre of there arc due to the current in portion AB will be
  A)
             \[\frac{{{\mu }_{0}}i}{r}\]        done clear
  B)
             \[\frac{{{\mu }_{0}}i}{2r}\] done clear
  C)
             \[\frac{{{\mu }_{0}}i}{4r}\]     done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer21)
  In the above question, the magnetic induction at O due to the whole length of the conductor is [MP PMT/PET 1998; RPET 2002]
  A)
             \[\frac{{{\mu }_{0}}i}{r}\]        done clear
  B)
             \[\frac{{{\mu }_{0}}i}{2r}\] done clear
  C)
             \[\frac{{{\mu }_{0}}i}{4r}\]     done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer22)
  In the figure shown there are two semicircles of radii \[{{r}_{1}}\] and \[{{r}_{2}}\] in which a current i is flowing. The magnetic induction  at the centre O will be
  A)
             \[\frac{{{\mu }_{0}}i}{r}({{r}_{1}}+{{r}_{2}})\] done clear
  B)
             \[\frac{{{\mu }_{0}}i}{4}({{r}_{1}}-{{r}_{2}})\] done clear
  C)
             \[\frac{{{\mu }_{0}}i}{4}\left( \frac{{{r}_{1}}+{{r}_{2}}}{{{r}_{1}}{{r}_{2}}} \right)\] done clear
  D)
             \[\frac{{{\mu }_{0}}i}{4}\left( \frac{{{r}_{2}}-{{r}_{1}}}{{{r}_{1}}{{r}_{2}}} \right)\] done clear
  View Solution play_arrow

• question_answer23)
  The magnetic moment of a current carrying loop is \[2.1\times {{10}^{-25}}\,amp\times {{m}^{2}}\]. The magnetic field at a point on its axis at a distance of \[1\,{AA}\] is
  A)
  \[4.2\times {{10}^{-2}}\,weber/{{m}^{2}}\]                done clear
  B)
  \[4.2\times {{10}^{-3}}\,weber/{{m}^{2}}\] done clear
  C)
  \[4.2\times {{10}^{-4}}\,weber/{{m}^{2}}\]                done clear
  D)
  \[4.2\times {{10}^{-5}}\,weber/{{m}^{2}}\] done clear
  View Solution play_arrow

• question_answer24)
  Two straight horizontal parallel wires are carrying the same current in the same direction, d is the distance between the wires. You are provided with a small freely suspended magnetic needle. At which of the following positions will the orientation of the needle be independent of the magnitude of the current in the wires [NCERT 1983]
  A)
             At a distance \[d/2\] from any of the wires done clear
  B)
             At a distance \[d/2\] from any of the wires in the horizontal plane done clear
  C)
             Anywhere on the circumference of a vertical circle of radius d and centre halfway between the wires done clear
  D)
             At points halfway between the wires in the horizontal plane done clear
  View Solution play_arrow

• question_answer25)
  A particle carrying a charge equal to 100 times the charge on an electron is rotating per second in a circular path of radius 0.8 metre. The value of the magnetic field produced at the centre will be \[({{\mu }_{0}}=\] permeability for vacuum) [CPMT 1986; KCET 2001; BHU 2001]
  A)
             \[\frac{{{10}^{-7}}}{{{\mu }_{0}}}\]                                 done clear
  B)
             \[{{10}^{-17}}{{\mu }_{0}}\] done clear
  C)
             \[{{10}^{-6}}{{\mu }_{0}}\]     done clear
  D)
             \[{{10}^{-7}}{{\mu }_{0}}\] done clear
  View Solution play_arrow

• question_answer26)
  A circular coil of radius R carries an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance r from the centre of the coil, such that r >> R, varies as        [EAMCET 1987; AIIMS 2004]
  A)
             \[\frac{1}{r}\]                       done clear
  B)
             \[\frac{1}{{{r}^{3/2}}}\] done clear
  C)
             \[\frac{1}{{{r}^{2}}}\]        done clear
  D)
             \[\frac{1}{{{r}^{3}}}\] done clear
  View Solution play_arrow

• question_answer27)
  In hydrogen atom, an electron is revolving in the orbit of radius \[0.53\,{AA}\] with \[6.6\times {{10}^{15}}\]rotations/second. Magnetic field produced at the centre of the orbit is        [MP PET 2003]
  A)
  \[0.125\,wb/{{m}^{2}}\]  done clear
  B)
  \[1.25\,wb/{{m}^{2}}\] done clear
  C)
  \[12.5\,wb/{{m}^{2}}\]     done clear
  D)
  \[125\,wb/{{m}^{2}}\] done clear
  View Solution play_arrow

• question_answer28)
  The magnetic induction due to an infinitely long straight wire carrying a current i at a distance r from wire is given by                   [MP PET 1994]
  A)
             \[|B|\,=\left( \frac{{{\mu }_{0}}}{4\pi } \right)\frac{2i}{r}\]               done clear
  B)
             \[|B|\,=\left( \frac{{{\mu }_{0}}}{4\pi } \right)\frac{r}{2i}\] done clear
  C)
             \[|B|\,=\left( \frac{4\pi }{{{\mu }_{0}}} \right)\frac{2i}{r}\]               done clear
  D)
             \[|B|\,=\left( \frac{4\pi }{{{\mu }_{0}}} \right)\frac{r}{2i}\] done clear
  View Solution play_arrow

• question_answer29)
  Magnetic effect of current was discovered by [MP PET 1994]
  A)
             Faraday                                   done clear
  B)
             Oersted done clear
  C)
             Ampere                                  done clear
  D)
             Bohr done clear
  View Solution play_arrow

• question_answer30)
  Two concentric circular coils of ten turns each are situated in the same plane. Their radii are 20 and 40 cm and they carry respectively 0.2 and 0.3 ampere current in opposite direction. The magnetic field in \[weber/{{m}^{2}}\] at the centre is [MP PMT 1994]
  A)
             \[\frac{35}{4}{{\mu }_{0}}\]   done clear
  B)
             \[\frac{{{\mu }_{0}}}{80}\] done clear
  C)
             \[\frac{7}{80}{{\mu }_{0}}\]   done clear
  D)
             \[\frac{5}{4}{{\mu }_{0}}\] done clear
  View Solution play_arrow

• question_answer31)
  A long solenoid has a radius a and number of turns per unit length is n. If it carries a current i, then the magnetic field on its axis is directly proportional to                                                         [MP PMT 1994]
  A)
             ani done clear
  B)
             ni done clear
  C)
             \[\frac{ni}{a}\]                     done clear
  D)
             \[{{n}^{2}}i\] done clear
  View Solution play_arrow

• question_answer32)
  A cell is connected between two points of a uniformly thick circular conductor. The magnetic field at the centre of the loop will be                                                                  [MP PMT 1994]
  A)
             Zero                                          done clear
  B)
             \[\frac{{{\mu }_{0}}}{2a}({{i}_{1}}-{{i}_{2}})\] done clear
  C)
             \[\frac{{{\mu }_{0}}}{2a}({{i}_{1}}+{{i}_{2}})\]            done clear
  D)
             \[\frac{{{\mu }_{0}}}{a}({{i}_{1}}+{{i}_{2}})\] (Here \[{{i}_{1}}\] and \[{{i}_{2}}\] are the currents flowing in the two parts of the circular conductor of radius ?a? and \[{{\mu }_{0}}\] has the usual meaning) done clear
  View Solution play_arrow

• question_answer33)
  A long solenoid is formed by winding 20 turns/cm. The current necessary to produce a magnetic field of 20 millitesla inside the solenoid will be approximately \[(\frac{{{\mu }_{0}}}{4\pi }={{10}^{-7}}\,tesla-metre/ampere)\]              [MP PMT 1994]
  A)
             8.0 A                                         done clear
  B)
             4.0 A done clear
  C)
             2.0 A                                         done clear
  D)
             1.0 A done clear
  View Solution play_arrow

• question_answer34)
  A battery is connected between two points A and B on the circumference of a uniform conducting ring of radius r and resistance R. One of the arcs AB of the ring subtends an angle \[\theta \] at the centre. The value of the magnetic induction at the centre due to the current in the ring is [IIT 1995]
  A)
             Proportional to \[2\,(180{}^\circ -\theta )\] done clear
  B)
             Inversely proportional to r done clear
  C)
             Zero, only if \[\theta =180{}^\circ \] done clear
  D)
             Zero for all values of \[\theta \] done clear
  View Solution play_arrow

• question_answer35)
  A current of 1 ampere is passed through a straight wire of length 2.0 metres. The magnetic field at a point in air at a distance of 3 metres from either end of wire and lying on the axis of wire will be                                               [MP PET 1995]
  A)
             \[\frac{{{\mu }_{0}}}{2\pi }\] done clear
  B)
             \[\frac{{{\mu }_{0}}}{4\pi }\] done clear
  C)
             \[\frac{{{\mu }_{0}}}{8\pi }\] done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer36)
  A long copper tube of inner radius R carries a current i. The magnetic field B inside the tube is     [MP PMT 1995]
  A)
             \[\frac{{{\mu }_{0}}i}{2\pi R}\]                                          done clear
  B)
             \[\frac{{{\mu }_{0}}i}{4\pi R}\] done clear
  C)
             \[\frac{{{\mu }_{0}}i}{2R}\]    done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer37)
  A straight wire of length \[({{\pi }^{2}})\] metre is carrying a current of 2A and the magnetic field due to it is measured at a point distant 1 cm from it. If the wire is to be bent into a circle and is to carry the same current as before, the ratio of the magnetic field at its centre to that obtained in the first case would be                                       [Haryana CEE 1996]
  A)
             50 : 1                                         done clear
  B)
             1 : 50 done clear
  C)
             100 : 1                                      done clear
  D)
             1 : 100 done clear
  View Solution play_arrow

• question_answer38)
  The direction of magnetic lines of forces close to a straight conductor carrying current will be      [RPMT 2002; RPET 2003; MP PET 2003]
  A)
             Along the length of the conductor done clear
  B)
             Radially outward done clear
  C)
             Circular in a plane perpendicular to the conductor done clear
  D)
             Helical done clear
  View Solution play_arrow

• question_answer39)
  If the strength of the magnetic field produced 10cm away from a infinitely long straight conductor is \[{{10}^{-5}}\,Weber/{{m}^{2}}\], the value of the current flowing in the conductor will be [MP PET 1996]
  A)
             5 ampere                                done clear
  B)
             10 ampere done clear
  C)
             500 ampere                           done clear
  D)
             1000 ampere done clear
  View Solution play_arrow

• question_answer40)
  Due to 10 ampere of current flowing in a circular coil of 10 cm radius, the magnetic field produced at its centre is \[3.14\times {{10}^{-3}}\,Weber/{{m}^{2}}\]. The number of turns in the coil will be                                                        [MP PET 1996]
  A)
             5000                                          done clear
  B)
             100 done clear
  C)
             50   done clear
  D)
             25 done clear
  View Solution play_arrow

• question_answer41)
  There are 50 turns of a wire in every cm length of a long solenoid. If 4 ampere current is flowing in the solenoid, the approximate value of magnetic field along its axis at an internal point and at one end will be respectively [MP PET 1996]
  A)
             \[12.6\times {{10}^{-3}}\,Weber/{{m}^{2}},\ 6.3\times {{10}^{-3}}\,Weber/{{m}^{2}}\] done clear
  B)
             \[12.6\times {{10}^{-3}}\,Weber/{{m}^{2}},\ 25.1\times {{10}^{-3}}\,Weber/{{m}^{2}}\] done clear
  C)
             \[25.1\times {{10}^{-3}}\,Weber/{{m}^{2}},\ 6.3\times {{10}^{-3}}\,Weber/{{m}^{2}}\] done clear
  D)
             \[25.1\times {{10}^{-5}}\,Weber/{{m}^{2}},\ 6.3\times {{10}^{-5}}\,Weber/{{m}^{2}}\] done clear
  View Solution play_arrow

• question_answer42)
  A solenoid is 1.0 metre long and it has 4250 turns. If a current of 5.0 ampere is flowing through it, what is the magnetic field at its centre \[[{{\mu }_{0}}=4\pi \times {{10}^{-7}}\,weber/amp-m]\] [MP PMT 1996]
  A)
             \[5.4\times {{10}^{-2}}\,weber/{{m}^{2}}\]                done clear
  B)
             \[2.7\times {{10}^{-2}}\,weber/{{m}^{2}}\] done clear
  C)
             \[1.35\times {{10}^{-2}}\,weber/{{m}^{2}}\]              done clear
  D)
             \[0.675\times {{10}^{-2}}\,weber/{{m}^{2}}\] done clear
  View Solution play_arrow

• question_answer43)
  A vertical wire kept in Z-X plane carries a current from Q to P (see figure). The magnetic field due to current will have the direction at the origin O along
  A)
             \[OX\] done clear
  B)
             \[OX'\] done clear
  C)
             \[OY\] done clear
  D)
             \[OY'\] done clear
  View Solution play_arrow

• question_answer44)
  One metre length of wire carries a constant current. The wire is bent to form a circular loop. The magnetic field at the centre of this loop is B. The same is now bent to form a circular loop of smaller radius to have four turns in the loop. The magnetic field at the centre of this new loop is
  A)
             4 B  done clear
  B)
             16 B done clear
  C)
             \[B/2\]                                     done clear
  D)
             \[B/4\] done clear
  View Solution play_arrow

• question_answer45)
  In a hydrogen atom, an electron moves in a circular orbit of radius \[5.2\times {{10}^{-11}}\,m\] and produces a magnetic induction of 12.56 T at its nucleus. The current produced by the motion of the electron will be (Given \[{{\mu }_{0}}=4\pi \times {{10}^{-7}}\,Wb/A-m)\] [MP PET 1997]
  A)
             \[6.53\times {{10}^{-3}}\,ampere\]                                done clear
  B)
             \[13.25\times {{10}^{-10}}\,ampere\] done clear
  C)
             \[9.6\times {{10}^{6}}\,ampere\]                                    done clear
  D)
             \[1.04\times {{10}^{-3}}\,ampere\] done clear
  View Solution play_arrow

• question_answer46)
  An arc of a circle of radius R subtends an angle \[\frac{\pi }{2}\] at the centre. It carries a current i. The magnetic field at the centre will be                                                  [MP PET 2003]
  A)
             \[\frac{{{\mu }_{0}}i}{2R}\]    done clear
  B)
             \[\frac{{{\mu }_{0}}i}{8R}\] done clear
  C)
             \[\frac{{{\mu }_{0}}i}{4R}\]    done clear
  D)
             \[\frac{2{{\mu }_{0}}i}{5R}\] done clear
  View Solution play_arrow

• question_answer47)
  At a distance of 10 cm from a long straight wire carrying current, the magnetic field is 0.04 T. At the distance of 40 cm, the magnetic field will be                                      [MP PMT 1997]
  A)
             0.01 T                                       done clear
  B)
             0.02 T done clear
  C)
             0.08 T                                       done clear
  D)
             0.16 T done clear
  View Solution play_arrow

• question_answer48)
  A uniform wire is bent in the form of a circle of radius R. A current I enters at A and leaves at C as shown in the figure : If the length ABC is half of the length ADC, the magnetic field at the centre O will be                                       [MP PMT 1997]
  A)
             Zero done clear
  B)
             \[\frac{{{\mu }_{0}}I}{2R}\] done clear
  C)
             \[\frac{{{\mu }_{0}}I}{4R}\] done clear
  D)
             \[\frac{{{\mu }_{0}}I}{6R}\] done clear
  View Solution play_arrow

• question_answer49)
  The magnetic induction at any point due to a long straight wire carrying a current is          [MP PMT/PET 1998]
  A)
             Proportional to the distance from the wire done clear
  B)
             Inversely proportional to the distance from wire done clear
  C)
             Inversely proportional to the square of the distance from the wire done clear
  D)
             Does not depend on distance done clear
  View Solution play_arrow

• question_answer50)
  The expression for magnetic induction inside a solenoid of length L carrying a current I and having N number of turns is                                                                                            [MP PMT/PET 1998]
  A)
     \[\frac{{{\mu }_{0}}}{4\pi }\frac{N}{LI}\]               done clear
  B)
     \[{{\mu }_{0}}NI\] done clear
  C)
     \[\frac{{{\mu }_{0}}}{4\pi }NLI\]                               done clear
  D)
    \[{{\mu }_{0}}\frac{N}{L}I\] done clear
  View Solution play_arrow

• question_answer51)
  In a current carrying long solenoid, the field produced does not depend upon                                    [MP PET 1999]
  A)
     Number of turns per unit length done clear
  B)
     Current flowing done clear
  C)
     Radius of the solenoid done clear
  D)
     All of the above three done clear
  View Solution play_arrow

• question_answer52)
  The earth's magnetic induction at a certain point is \[7\times {{10}^{-5}}Wb/{{m}^{2}}.\] This is to be annulled by the magnetic induction at the centre of a circular conducting loop of radius 5 cm. The required current in the loop is [MP PET 1999; MP PMT 2002]
  A)
     0.56 A                               done clear
  B)
     5.6 A done clear
  C)
     0.28 A                               done clear
  D)
     2.8 A done clear
  View Solution play_arrow

• question_answer53)
  Magnetic field due to 0.1 A current flowing through a circular coil of radius 0.1 m and 1000 turns at the centre of the coil is                                               [CBSE PMT 1999]
  A)
     \[2\times {{10}^{-1}}\,T\]                                            done clear
  B)
     \[4.31\times {{10}^{-2}}\,T\] done clear
  C)
     \[6.28\times {{10}^{-4}}\,T\]                                      done clear
  D)
     \[9.81\times {{10}^{-4}}\,T\] done clear
  View Solution play_arrow

• question_answer54)
  Magnetic field intensity at the centre of coil of 50 turns, radius 0.5 m and carrying a current of 2 A is [CBSE PMT 1999; BHU 2002]
  A)
     \[0.5\times {{10}^{-5}}\,T\]                                        done clear
  B)
     \[1.25\times {{10}^{-4}}\,T\] done clear
  C)
     \[3\times {{10}^{-5}}\,T\]                                            done clear
  D)
     \[4\times {{10}^{-5}}\,T\] done clear
  View Solution play_arrow

• question_answer55)
  A circular coil ?A? has a radius R and the current flowing through it is I. Another circular coil ?B? has a radius 2R and if 2I is the current flowing through it, then the magnetic fields at the centre of the circular coil are in the ratio of (i.e.\[{{B}_{A}}\] to \[{{B}_{B}}\])                              [CBSE PMT1993; AIEEE 2002]
  A)
     4 : 1                                   done clear
  B)
     2 : 1 done clear
  C)
     3 : 1                                   done clear
  D)
     1 : 1 done clear
  View Solution play_arrow

• question_answer56)
  The magnetic field at a distance r from a long wire carrying current i is 0.4 Tesla. The magnetic field at a distance 2r is [CBSE PMT 1992; DPMT 2004]
  A)
     0.2 Tesla                          done clear
  B)
     0.8 Tesla done clear
  C)
     0.1 Tesla                          done clear
  D)
     1.6 Tesla done clear
  View Solution play_arrow

• question_answer57)
  A current I flows along the length of an infinitely long, straight and thin-walled pipe. Then            [IIT-JEE 1993]
  A)
     The magnetic field at all points inside the pipe is the same but not zero done clear
  B)
     The magnetic field at any point inside the pipe is zero done clear
  C)
     The magnetic field is zero only on the axis of the pipe done clear
  D)
     The magnetic field is different at different points inside the pipe done clear
  View Solution play_arrow

• question_answer58)
  The magnetic field at the centre of current carrying coil is [CPMT 1996; RPET 2002, 03]
  A)
     \[\frac{{{\mu }_{0}}ni}{2r}\]                                       done clear
  B)
     \[\frac{{{\mu }_{0}}}{2\pi }\frac{ni}{r}\] done clear
  C)
     \[\frac{{{\mu }_{0}}ni}{4r}\]                                       done clear
  D)
     \[{{\mu }_{0}}ni\] done clear
  View Solution play_arrow

• question_answer59)
  A straight wire of diameter 0.5 mm carrying a current of 1 A is replaced by another wire of 1 mm diameter carrying the same current. The strength of magnetic field far away is [CBSE PMT 1997, 99]
  A)
     Twice the earlier value done clear
  B)
     Half of the earlier value done clear
  C)
     Quarter of its earlier value done clear
  D)
     Unchanged done clear
  View Solution play_arrow

• question_answer60)
  A neutral point is obtained at the centre of a vertical circular coil carrying current. The angle between the plane of the coil and the magnetic meridian is                                                 [SCRA 1998]
  A)
     0                                         done clear
  B)
     45° done clear
  C)
     60°                                     done clear
  D)
     90° done clear
  View Solution play_arrow

• question_answer61)
  One Tesla is equal to                                   [AFMC 1998]
  A)
     \[{{10}^{7}}\,gauss\]  done clear
  B)
     \[{{10}^{-4}}\,gauss\] done clear
  C)
     \[{{10}^{4}}\,gauss\]  done clear
  D)
     \[{{10}^{-8}}\,gauss\] done clear
  View Solution play_arrow

• question_answer62)
  A current carrying wire in the neighborhood produces  [AFMC 1999]
  A)
     No field done clear
  B)
     Electric field only done clear
  C)
     Magnetic field only done clear
  D)
     Electric and magnetic fields done clear
  View Solution play_arrow

• question_answer63)
  Tesla is the unit of                                        [AIIMS 1999]
  A)
     Electric flux                    done clear
  B)
     Magnetic flux done clear
  C)
     Electric field                   done clear
  D)
     Magnetic field done clear
  View Solution play_arrow

• question_answer64)
  The magnetic induction in air at a point 1cm away from a long wire that carries a current of 1A, will be [BHU 1999]
  A)
     \[1\times {{10}^{-5}}T\]   done clear
  B)
     \[2\times {{10}^{-5}}T\] done clear
  C)
     \[3\times {{10}^{-5}}T\]   done clear
  D)
     \[4\times {{10}^{-5}}T\] done clear
  View Solution play_arrow

• question_answer65)
  The magnetic field at the centre of coil of n turns, bent in the form of a square of side 2l , carrying current i, is                                                                    [AMU (Engg.) 1999]
  A)
     \[\frac{\sqrt{2}{{\mu }_{0}}nI}{\pi l}\] done clear
  B)
     \[\frac{\sqrt{2}{{\mu }_{0}}nI}{2\pi l}\] done clear
  C)
     \[\frac{\sqrt{2}{{\mu }_{0}}nI}{4\pi l}\]                 done clear
  D)
     \[\frac{2{{\mu }_{0}}nI}{\pi l}\] done clear
  View Solution play_arrow

• question_answer66)
  Which of the following gives the value of magnetic field according to,  Biot-Savart?s law?                                [BHU 2000]
  A)
     \[\frac{i\Delta l\sin \theta }{{{r}^{2}}}\]                done clear
  B)
     \[\frac{{{\mu }_{0}}}{4\pi }\frac{i\Delta l\sin \theta }{r}\] done clear
  C)
     \[\frac{{{\mu }_{0}}}{4\pi }\frac{i\Delta l\sin \theta }{{{r}^{2}}}\]            done clear
  D)
     \[\frac{{{\mu }_{0}}}{4\pi }i\Delta l\sin \theta \] done clear
  View Solution play_arrow

• question_answer67)
  A toroid has number of turns per unit length n, current i, then the magnetic field is                          [RPET 2000]
  A)
     \[{{\mu }_{0}}ni\]        done clear
  B)
     \[{{\mu }_{0}}{{n}^{2}}i\] done clear
  C)
     \[{{\mu }_{0}}i/n\]      done clear
  D)
     None of these done clear
  View Solution play_arrow

• question_answer68)
  Magnetic field due to a ring having n turns at a distance x on its axis is proportional to (if r = radius of ring) [RPET 2000]
  A)
     \[\frac{r}{({{x}^{2}}+{{r}^{2}})}\]                              done clear
  B)
     \[\frac{{{r}^{2}}}{{{({{x}^{2}}+{{r}^{2}})}^{3/2}}}\] done clear
  C)
     \[\frac{n{{r}^{2}}}{{{({{x}^{2}}+{{r}^{2}})}^{3/2}}}\]       done clear
  D)
     \[\frac{{{n}^{2}}{{r}^{2}}}{{{({{x}^{2}}+{{r}^{2}})}^{3/2}}}\] done clear
  View Solution play_arrow

• question_answer69)
  A and B are two concentric circular conductors of centre O and carrying currents \[{{I}_{1}}\] and \[{{i}_{2}}\] as shown in the adjacent figure. If ratio of their radii is 1 : 2 and ratio of the flux densities at O due to A and B  is 1 : 3, then the value of \[{{i}_{1}}/{{i}_{2}}\] is                  [KCET 2000]
  A)
     \[\frac{1}{6}\] done clear
  B)
     \[\frac{1}{4}\] done clear
  C)
     \[\frac{1}{3}\] done clear
  D)
     \[\frac{1}{2}\] done clear
  View Solution play_arrow

• question_answer70)
  A long straight wire carries an electric current of 2A. The magnetic induction at a perpendicular distance of 5m from the wire is                              [EAMCET (Med.) 2000]
  A)
     \[4\times {{10}^{-8}}T\]   done clear
  B)
     \[8\times {{10}^{-8}}T\] done clear
  C)
     \[12\times {{10}^{-8}}T\] done clear
  D)
     \[16\times {{10}^{-8}}T\] done clear
  View Solution play_arrow

• question_answer71)
  A straight wire carrying a current 10 A is bent into a semicircular arc of radius 5 cm. The magnitude of magnetic field at the center is                                     [CPMT 2000]
  A)
     \[1.5\times {{10}^{-5}}\,T\]                                        done clear
  B)
     \[3.14\times {{10}^{-5}}\,T\] done clear
  C)
     \[6.28\times {{10}^{-5}}\,T\]                                      done clear
  D)
     \[19.6\times {{10}^{-5}}T\] done clear
  View Solution play_arrow

• question_answer72)
  A long solenoid of length L has a mean diameter D. It has n layers of windings of N turns each. If it carries a current ?i? the magnetic field at its centre will be [MP PMT 2000]
  A)
     Proportional to D done clear
  B)
     Inversely proportional to D done clear
  C)
     Independent of D done clear
  D)
     Proportional to L done clear
  View Solution play_arrow

• question_answer73)
  A circular loop of radius 0.0157m carries a current of 2.0 amp. The magnetic field at the centre of the loop is   \[({{\mu }_{0}}=4\pi \times {{10}^{-7}}\,weber/amp-m)\]                            [MP PET 2000]
  A)
     \[\text{1}\text{.57}\times \text{10}{{\text{ }}^{\text{-5}}}\,weber/{{m}^{2}}\]               done clear
  B)
     \[8.0\times \text{10}{{\text{ }}^{\text{-5}}}\,weber/{{m}^{2}}\] done clear
  C)
     \[2.5\times \text{10}{{\text{ }}^{\text{-5}}}\,weber/{{m}^{2}}\]            done clear
  D)
     \[\text{3}.14\times \text{10}{{\text{ }}^{\text{-5}}}\,weber/{{m}^{2}}\] done clear
  View Solution play_arrow

• question_answer74)
  A long solenoid has 200 turns per cm and carries a current of 2.5 amps. The magnetic field at its centre is \[({{\mu }_{0}}=4\pi \times {{10}^{-7}}\,weber/amp\text{-}m)\]                              [MP PET 2000]
  A)
     \[3.14\times {{10}^{-2}}weber/{{m}^{2}}\] done clear
  B)
     \[6.28\times {{10}^{-2}}weber/{{m}^{2}}\] done clear
  C)
     \[9.42\times {{10}^{-2}}weber/{{m}^{2}}\] done clear
  D)
     \[12.56\times {{10}^{-2}}weber/\,{{m}^{2}}\] done clear
  View Solution play_arrow

• question_answer75)
  Two concentric coplanar circular loops of radii \[{{r}_{1}}\] and \[{{r}_{2}}\] carry currents of respectively \[{{i}_{1}}\] and \[{{i}_{2}}\] in opposite directions (one clockwise and the other anticlockwise.) The magnetic induction at the centre of the loops is half that due to \[{{i}_{1}}\] alone at the centre. If \[{{r}_{2}}=2{{r}_{1}}.\] the value of \[{{I}_{2}}/{{I}_{1}}\] is    [MP PET 2000]
  A)
     2                                         done clear
  B)
     1/2 done clear
  C)
     1/4                                     done clear
  D)
     1 done clear
  View Solution play_arrow

• question_answer76)
  PQRS is a square loop made of uniform conducting wire the current enters the loop at P and leaves at S.  Then the magnetic field will be                                                    [KCET 2000]
  A)
             Maximum at the centre of the loop done clear
  B)
             Zero at the centre of loop done clear
  C)
             Zero at all points inside the loop done clear
  D)
             Zero at all points outside of the loop done clear
  View Solution play_arrow

• question_answer77)
  Magnetic fields at two points on the axis of a circular coil at a distance of 0.05m and 0.2m from the centre are in the ratio 8 : 1. The radius of the coil is  [KCET 2002]
  A)
             1.0 m                                        done clear
  B)
             0.1 m done clear
  C)
             0.15 m                                      done clear
  D)
             0.2 m done clear
  View Solution play_arrow

• question_answer78)
  An electric current passes through a long straight wire. At a distance 5 cm from the wire, The magnetic field is B. The field at 20 cm  from the wire would be     [CPMT 2001; Pb PET 2002]
  A)
             \[\frac{B}{6}\]                      done clear
  B)
             \[\frac{B}{4}\] done clear
  C)
             \[\frac{B}{3}\]                      done clear
  D)
             \[\frac{B}{2}\] done clear
  View Solution play_arrow

• question_answer79)
  A closely wound flat circular coil of 25 turns of wire has diameter of 10 cm and carries a current of 4 ampere. Determine the flux density at the centre of a coil  [AIIMS 2001]
  A)
             \[1.679\times {{10}^{-5}}tesla\]                                       done clear
  B)
             \[2.028\times {{10}^{-4}}tesla\] done clear
  C)
             \[1.257\times {{10}^{-3}}tesla\]                                       done clear
  D)
             \[1.512\times {{10}^{-6}}tesla\] done clear
  View Solution play_arrow

• question_answer80)
  The dimension of the magnetic field intensity B is  [MP PET 2001]
  A)
             \[ML{{T}^{-2}}{{A}^{-1}}\]      done clear
  B)
             \[M{{T}^{-2}}{{A}^{-1}}\] done clear
  C)
             \[M{{L}^{2}}T{{A}^{-2}}\] done clear
  D)
             \[{{M}^{2}}L{{T}^{-2}}{{A}^{-1}}\] done clear
  View Solution play_arrow

• question_answer81)
  A current of 2 amp. flows in a long, straight wire of radius 2 mm. The intensity of magnetic field on the axis of the wire is                                                                   [MP PET 2001]
  A)
             \[\left( \frac{{{\mu }_{o}}}{\pi } \right)\times {{10}^{3}}\]Tesla       done clear
  B)
             \[\left( \frac{{{\mu }_{o}}}{2\pi } \right)\times {{10}^{3}}\]Tesla done clear
  C)
             \[\left( \frac{2{{\mu }_{o}}}{\pi } \right)\times {{10}^{3}}\]Tesla     done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer82)
  The magnetic field at the centre of a circular coil of radius r carrying current I is \[{{B}_{1}}\]. The field at the centre of another coil of radius 2 r carrying same current I is \[{{B}_{2}}\]. The ratio \[\frac{{{B}_{1}}}{{{B}_{2}}}\] is                                                                            [MP PET 2001]
  A)
             \[\frac{1}{2}\]                       done clear
  B)
             1 done clear
  C)
             2     done clear
  D)
             4 done clear
  View Solution play_arrow

• question_answer83)
  1A current flows through an infinitely long straight wire. The magnetic field produced at a point 1 metres away from it is  [MP PMT 2001]
  A)
             \[2\times {{10}^{-3}}\,Tesla\]                                            done clear
  B)
             \[\frac{2}{10}\,Tesla\] done clear
  C)
             \[2\times {{10}^{-7}}\,Tesla\]                                            done clear
  D)
             \[2\pi \times {{10}^{-6}}\,\text{Tesla}\] done clear
  View Solution play_arrow

• question_answer84)
  Two infinitely long parallel wires carry equal current in same direction. The magnetic field at a mid point in between the two wires is                                                         [MP PMT 2001]
  A)
             Twice the magnetic field produced due to each of the wires done clear
  B)
             Half of the magnetic field produced due to each of the wires done clear
  C)
             Square of the magnetic field produced due to each of the wires done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer85)
  A wire in the form of a square of side ?a? carries a current i. Then the magnetic induction at the centre of the square wire is (Magnetic permeability of free space =\[{{\mu }_{o}})\] [EAMCET 2001]
  A)
             \[\frac{{{\mu }_{0}}i}{2\pi a}\]                                          done clear
  B)
             \[\frac{{{\mu }_{0}}i\sqrt{2}}{\pi a}\] done clear
  C)
             \[\frac{2\sqrt{2}{{\mu }_{o}}i}{\pi a}\]                          done clear
  D)
             \[\frac{{{\mu }_{0}}i}{\sqrt{2}\pi \,a}\] done clear
  View Solution play_arrow

• question_answer86)
  What should be the current in a circular coil of radius 5cm to annul \[{{B}_{H}}=5\times {{10}^{-5}}T\]                                         [DCE 2001]
  A)
             0.4 A                                         done clear
  B)
             4 A done clear
  C)
             40 A                                          done clear
  D)
             1 A done clear
  View Solution play_arrow

• question_answer87)
  A current of 0.1 A circulates around a coil of 100 turns and having a radius equal to 5cm. The magnetic field set up at the centre of the coil is (m0 = 4p ´ 10?7 weber/amp-metre) [DPMT 2002]
  A)
             2 ´ 10?5 Tesla                         done clear
  B)
             4 ´ 10?5 Tesla done clear
  C)
             8p ´ 10?5 Tesla                      done clear
  D)
             4p ´ 10?5 Tesla done clear
  View Solution play_arrow

• question_answer88)
  An electron moving in a circular orbit of radius r makes n rotation per second. The magnetic field produced at the centre has a magnitude of          [KCET 2001; UPSEAT 2001, 02]
  A)
             \[\frac{{{\mu }_{0}}ne}{2r}\]                                             done clear
  B)
             \[\frac{{{\mu }_{0}}{{n}^{2}}e}{2r}\] done clear
  C)
             \[\frac{{{\mu }_{0}}ne}{2\pi r}\]                                      done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer89)
  A long solenoid has n turns per meter and current I A is flowing through it. The magnetic field at the ends of the solenoid is                                             [MP PMT 2001; MP PET 2002]                                             
  A)
             \[\frac{{{\mu }_{0}}nI}{2}\]    done clear
  B)
             \[{{\mu }_{0}}nI\] done clear
  C)
             Zero                                          done clear
  D)
             \[2{{\mu }_{0}}nI\] done clear
  View Solution play_arrow

• question_answer90)
  A wire carrying current i is shaped as shown. Section AB is a quarter circle of radius r.  The magnetic field is directed [KCET 2002]
  A)
             At an angle \[\pi /4\] to the plane of the paper done clear
  B)
             Perpendicular to the plane of the paper and directed in to the paper done clear
  C)
             Along the bisector of the angle ACB towards AB done clear
  D)
             Along the bisector of the angle ACB away from AB done clear
  View Solution play_arrow

• question_answer91)
  Two long straight wires are set parallel to each other. Each carries a current i in the same direction and the separation between them is 2r. The intensity of the magnetic field midway between them is [Kerala PET 2002; DCE 2002]
  A)
             \[{{\mu }_{o}}i/r\] done clear
  B)
             \[4{{\mu }_{o}}i/r\] done clear
  C)
             Zero done clear
  D)
             \[{{\mu }_{o}}i/4r\] done clear
  View Solution play_arrow

• question_answer92)
  A magnetic field can be produced by                    [AIEEE 2002]
  A)
             A moving charge                 done clear
  B)
             A changing electric field done clear
  C)
             None of these                      done clear
  D)
             Both of these done clear
  View Solution play_arrow

• question_answer93)
    Unit of magnetic permeability is                             [AFMC 2002]
  A)
             Amp/metre                           done clear
  B)
             Amp/\[{{m}^{2}}\] done clear
  C)
             Henry                                       done clear
  D)
             Henry/metre done clear
  View Solution play_arrow

• question_answer94)
  A long straight wire carries a current of \[\pi \,amp.\] The magnetic field due to it will be \[5\times {{10}^{-5}}\text{ }weber/{{m}^{\text{2}}}\] at what distance from the wire \[[{{\mu }_{o}}=\]permeability of air]  [MP PMT 2002]
  A)
             \[{{10}^{4}}{{\mu }_{o}}\] metre                                      done clear
  B)
             \[\frac{{{10}^{4}}}{{{\mu }_{o}}}\] metre done clear
  C)
             \[{{10}^{6}}{{\mu }_{o}}\] metre                                      done clear
  D)
             \[\frac{{{10}^{6}}}{{{\mu }_{o}}}\]metre done clear
  View Solution play_arrow

• question_answer95)
  When a certain length of wire is turned into one circular loop, the magnetic induction at the centre of coil due to some current flowing is \[{{B}_{1}}\] If the same wire is turned into three loops to make a circular coil, the magnetic induction at the center of this coil for the same current will be  [MP PMT 2002]
  A)
             \[{{B}_{1}}\]                          done clear
  B)
             \[9\,{{B}_{1}}\] done clear
  C)
             \[3\,{{B}_{1}}\]                    done clear
  D)
             \[27\,{{B}_{1}}\] done clear
  View Solution play_arrow

• question_answer96)
  Gauss is unit of which quantity        [MP PET 2002]
  A)
             H     done clear
  B)
             B done clear
  C)
             \[\varphi \]                            done clear
  D)
             I done clear
  View Solution play_arrow

• question_answer97)
  On connecting a battery to the two corners of a diagonal of a square conductor frame of side \[a\] the magnitude of the magnetic field at the centre will be             [MP PET 2002]
  A)
             Zero                                          done clear
  B)
             \[\frac{{{\mu }_{o}}}{\pi a}\] done clear
  C)
             \[\frac{2{{\mu }_{o}}}{\pi a}\]                                           done clear
  D)
             \[\frac{4{{\mu }_{o}}i}{\pi a}\] done clear
  View Solution play_arrow

• question_answer98)
  The ratio of the magnetic field at the centre of a current carrying coil of the radius a and at a distance ?a? from centre of the coil and perpendicular to the axis of coil is  [MP PET 2002]
  A)
             \[\frac{1}{\sqrt{2}}\]         done clear
  B)
             \[\sqrt{2}\] done clear
  C)
             \[\frac{1}{2\sqrt{2}}\]       done clear
  D)
             \[2\sqrt{2}\] done clear
  View Solution play_arrow

• question_answer99)
  A part of a long wire carrying a current i is bent into a circle of radius r as shown in figure. The net magnetic field at the centre O of the circular loop is                              [UPSEAT 2002]
  A)
             \[\frac{{{\mu }_{o}}i}{4r}\] done clear
  B)
             \[\frac{{{\mu }_{o}}i}{2r}\] done clear
  C)
             \[\frac{{{\mu }_{o}}i}{2\pi r}(\pi +1)\] done clear
  D)
             \[\frac{{{\mu }_{o}}i}{2\pi r}(\pi -1)\] done clear
  View Solution play_arrow

• question_answer100)
  The current in the windings on a toroid is 2.0A. There are 400 turns and the mean circumferential length is 40cm. If the inside magnetic field is 1.0T, the relative permeability is near to                                                 [AMU (Med.) 2002]
  A)
             100                                            done clear
  B)
             200 done clear
  C)
             300 done clear
  D)
             400 done clear
  View Solution play_arrow

• question_answer101)
  ?On flowing current in a conducting wire the magnetic field produces around it.? It is a law of      [RPET 2003]
  A)
             Lenz done clear
  B)
             Ampere done clear
  C)
             Ohm                                         done clear
  D)
             Maxwell done clear
  View Solution play_arrow

• question_answer102)
  The magnetic field near a current carrying conductor is given by                                                [Orissa JEE 2003]
  A)
             Coulomb?s law                     done clear
  B)
             Lenz? law done clear
  C)
             Biot-savart?s law                  done clear
  D)
             Kirchoff?s law done clear
  View Solution play_arrow

• question_answer103)
  A current of 10A is passing through a long wire which has semicircular loop of the radius 20cm as shown in the figure. Magnetic field produced at the centre of the loop is    [Orissa JEE 2003]
  A)
             \[10\,\pi \mu T\] done clear
  B)
             \[5\,\pi \mu T\] done clear
  C)
             \[4\,\pi \mu T\]                   done clear
  D)
             \[2\,\pi \mu T\] done clear
  View Solution play_arrow

• question_answer104)
  A wire in the form of a circular loop of one turn carrying a current produces a magnetic field B at the centre. If the same wire is looped into a coil of two turns and carries the same current, the new value of magnetic induction at the centre is                                                           [CBSE 2002; KCET 2003]
  A)
             \[5B\]                                       done clear
  B)
             \[3B\] done clear
  C)
             \[2B\]                                       done clear
  D)
             \[4B\] done clear
  View Solution play_arrow

• question_answer105)
  A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, the new value of the magnetic field is [CBSE PMT 2003]
  A)
             B     done clear
  B)
             2 B done clear
  C)
             4 B  done clear
  D)
             B/2 done clear
  View Solution play_arrow

• question_answer106)
  A long straight wire carrying current of 30A is placed in an external uniform magnetic field of induction 4 ´ 10?4T. The magnetic field is acting parallel to the direction of current. The magnitude of the resultant magnetic induction in tesla at a point 2.0 cm away from the wire is            [EAMCET 2003]
  A)
             10?4                                           done clear
  B)
             3 ´ 10?4 done clear
  C)
             5 ´ 10?4                                    done clear
  D)
             6 ´ 10?4 done clear
  View Solution play_arrow

• question_answer107)
  The earth?s magnetic field at a given point is \[0.5\times {{10}^{-5}}Wb\text{-}{{m}^{-2}}\]. This field is to be annulled by magnetic induction at the center of a circular conducting loop of radius 5.0cm. The current required to be flown in the loop is nearly [AIIMS 2003]
  A)
             0.2 A                                         done clear
  B)
             0.4A done clear
  C)
             4A  done clear
  D)
             40A done clear
  View Solution play_arrow

• question_answer108)
  A coil having N turns carry a current I as shown in the figure. The magnetic field intensity at point P is [BHU 2003; CPMT 2004]
  A)
             \[\frac{{{\mu }_{0}}NI{{R}^{2}}}{2{{({{R}^{2}}+{{x}^{2}})}^{3/2}}}\]               done clear
  B)
             \[\frac{{{\mu }_{0}}NI}{2R}\] done clear
  C)
             \[\frac{{{\mu }_{0}}NI{{R}^{2}}}{{{(R+x)}^{2}}}\]      done clear
  D)
             Zero done clear
  View Solution play_arrow

• question_answer109)
  Two similar coils are kept mutually perpendicular such that their centres coincide. At the centre, find the ratio of the magnetic field due to one coil and the resultant magnetic field by both coils, if the same current is  flown [BHU 2003; CPMT 2004]
  A)
             1: \[\sqrt{2}\]                       done clear
  B)
             1 : 2 done clear
  C)
             2 : 1                                           done clear
  D)
             \[\sqrt{3}\,\,:\,\,1\] done clear
  View Solution play_arrow

• question_answer110)
  In the figure, what is the magnetic field at the point O   [MP PMT 2004]
  A)
             \[\frac{{{\mu }_{0}}I}{4\pi r}\] done clear
  B)
             \[\frac{{{\mu }_{0}}I}{4\pi r}+\frac{{{\mu }_{0}}I}{2\pi r}\] done clear
  C)
             \[\frac{{{\mu }_{0}}I}{4r}+\frac{{{\mu }_{0}}I}{4\pi r}\] done clear
  D)
             \[\frac{{{\mu }_{0}}I}{4r}-\frac{{{\mu }_{0}}I}{4\pi r}\] done clear
  View Solution play_arrow

• question_answer111)
  The magnetic moment of a current (i) carrying circular coil of radius (r) and number of turns (n) varies as               [AIIMS 2004]
  A)
             1/ r2                                          done clear
  B)
             1/ r done clear
  C)
             r      done clear
  D)
             r2 done clear
  View Solution play_arrow

• question_answer112)
  A current flows in a conductor from east to west. The direction of the magnetic field at a points above the conductor is.....                                                            [KCET 2004]
  A)
             Towards north                     done clear
  B)
             Towards south done clear
  C)
             Towards east                        done clear
  D)
             Towards west done clear
  View Solution play_arrow

• question_answer113)
  A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be              [AIEEE 2004]
  A)
             nB done clear
  B)
             n2B done clear
  C)
             2nB                                           done clear
  D)
             2n2B done clear
  View Solution play_arrow

• question_answer114)
  The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is 54 mT. What will be its value at the centre of the loop                                           [AIEEE 2004]
  A)
             250 m T                                     done clear
  B)
             150 m T done clear
  C)
             125 m T                                     done clear
  D)
             75 m T done clear
  View Solution play_arrow

• question_answer115)
  The magnetic induction at the centre of a current carrying circular of coil radius r, is                           [J & K CET 2004]
  A)
             Directly proportional to r  done clear
  B)
             Inversely proportional r  done clear
  C)
             Directly proportional to r2 done clear
  D)
             Inversely proportional to r2 done clear
  View Solution play_arrow

• question_answer116)
  The current is flowing in south direction along a power line. The direction of magnetic field above the power line (neglecting earth's field) is         [Pb. PMT 2004; Kerala PMT 2004]
  A)
             South                                       done clear
  B)
             East done clear
  C)
             North                                       done clear
  D)
             West done clear
  View Solution play_arrow

• question_answer117)
  Two wires of same length are shaped into a square and a circle. If they carry same current, ratio of the magnetic moment is                                                                           [DCE 2002]
  A)
             2 : p                                           done clear
  B)
             p : 2 done clear
  C)
             p : 4                                           done clear
  D)
             4 : p done clear
  View Solution play_arrow

• question_answer118)
  When the current flowing in a circular coil is doubled and the number of turns of the coil in it is halved, the magnetic field at its centre will become                                  [DPMT 2003]
  A)
             Four times                             done clear
  B)
             Same done clear
  C)
             Half                                           done clear
  D)
             Double done clear
  View Solution play_arrow

• question_answer119)
  An electron is revolving round a proton, producing a magnetic field of 16 weber/m2 in a circular orbit of radius 1Å. It?s angular velocity will be                        [RPMT 2002]
  A)
             1017 rad/sec                           done clear
  B)
             1/2p  ´ 1012 rad/sec done clear
  C)
             2 p ´ 1012 rad/sec                done clear
  D)
             4 p ´ 1012 rad/sec done clear
  View Solution play_arrow

• question_answer120)
  20 ampere current is flowing in a long straight wire. The intensity of magnetic field at a distance 10 cm from the wire will be                                                         [Pb. PMT 2003]                  
  A)
             4 ´ 10?5 Wb/m2                    done clear
  B)
             9 ´ 10?5 Wb/m2 done clear
  C)
             8 ´ 10?5 Wb/m2                    done clear
  D)
             6 ´ 10?5 Wb/m2 done clear
  View Solution play_arrow

• question_answer121)
  The field due to a long straight wire carrying a current I is proportional to                                              [MP PMT 1993]
  A)
             I      done clear
  B)
             \[{{I}^{3}}\] done clear
  C)
             \[\sqrt{I}\]                             done clear
  D)
             \[1/I\] done clear
  View Solution play_arrow

• question_answer122)
  Two concentric coils each of radius equal to \[2\pi \text{ }cm\] are placed at right angles to each other. 3 ampere and 4 ampere are the currents flowing in each coil respectively. The magnetic induction in \[Weber/{{m}^{2}}\] at the centre of the coils will be \[({{\mu }_{0}}=4\pi \times {{10}^{-7}}Wb/A.m)\]                         [AIEEE 2005]
  A)
             \[5\times {{10}^{-5}}\]      done clear
  B)
             \[7\times {{10}^{-5}}\] done clear
  C)
             \[12\times {{10}^{-5}}\]   done clear
  D)
             \[{{10}^{-5}}\] done clear
  View Solution play_arrow

• question_answer123)
  A wire carrying current I and other carrying 2I in the same direction produces a magnetic field B at the mid point. What will be the field when 2I wire is switched off    [AFMC 2005]
  A)
             B / 2                                          done clear
  B)
             2B done clear
  C)
             B     done clear
  D)
             4B done clear
  View Solution play_arrow

• question_answer124)
  Two long parallel wires P and Q are both perpendicular to the plane of the paper with distance 5 m between them. If P and Q carry current of 2.5 amp and 5 amp respectively in the same direction, then the magnetic field at a point half way between the wires is                                 [Kerala PMT 2005]
  A)
             \[\frac{\sqrt{3}{{\mu }_{0}}}{2\pi }\]                              done clear
  B)
             \[\frac{{{\mu }_{0}}}{\pi }\] done clear
  C)
             \[\frac{3{{\mu }_{0}}}{2\pi }\]                                           done clear
  D)
             \[\frac{{{\mu }_{0}}}{2\pi }\] done clear
  E)
  (e)     \[\frac{\sqrt{3}{{\mu }_{0}}}{\pi }\] done clear
  View Solution play_arrow

• question_answer125)
  The direction of magnetic lines of force produced by passing a direct current in a conductor is given by [J & K CET 2005]
  A)
             Lenz?s law                              done clear
  B)
             Fleming?s left hand rule done clear
  C)
             Right hand palm rule         done clear
  D)
             Maxwell?s law done clear
  View Solution play_arrow

• question_answer126)
  For the magnetic field to be maximum due to a small element of current carrying conductor at a point, the angle between the element and the line joining the element to the given point must be                                          [J & K CET 2005]
  A)
             0°    done clear
  B)
             90° done clear
  C)
             180°                                          done clear
  D)
             45° done clear
  View Solution play_arrow