JEE Main & Advanced Physics Electro Magnetic Induction Question Bank

done Self Evaluation Test - Electromagnetic Induction Total Questions - 100

• question_answer1)
  A conducting square loop is placed in a magnetic field B with its plane perpendicular to the field. The sides of the loop start shrinking at a constant rate \[\alpha \]. The induced emf in the loop at an instant when its side is 'a' is
  A)
  \[2a\alpha B\] done clear
  B)
  \[{{a}^{2}}\alpha B\] done clear
  C)
  \[2{{a}^{2}}\alpha B\] done clear
  D)
  \[a\alpha B\] done clear
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• question_answer2)
  A rectangular loop is present in the magnetic field region of an infinite long wire. Now the loop is being rotated as shown in the figure. Then the induced current in side AD will be
  A)
  along DA done clear
  B)
  along AD              done clear
  C)
  zero done clear
  D)
  None of these             done clear
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• question_answer3)
  A rod PQ of length L moves with a uniform velocity v parallel to a long straight wire carrying a current i, the end P remaining at a distance r from the wire. The emf induced across the rod is           
  A)
  \[\frac{{{\mu }_{0}}i{{v}^{2}}}{2\pi }ln\,\left( \frac{r+L}{R} \right)\] done clear
  B)
         \[\vec{B}\] done clear
  C)
  \[\frac{{{\mu }_{0}}iv}{2\pi }ln\,\left( \frac{r+L}{R} \right)\] done clear
  D)
         \[\frac{{{\mu }_{0}}iv}{2\pi }ln\,\left( \frac{{{r}^{2}}+{{L}^{2}}}{{{L}^{2}}} \right)\] done clear
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• question_answer4)
  A coil having n turns and resistance \[R\Omega \]. Is connected with a galvanometer of resistance\[4R\,\Omega \]. This combination is moved in time t second from a magnetic flux \[{{\phi }_{1}}\]weber to\[{{\phi }_{2}}\] weber. The induced current in the circuit is
  A)
  \[-\frac{{{\phi }_{2}}-{{\phi }_{1}}}{5\,Rnt}\]    done clear
  B)
  \[-\frac{n({{\phi }_{2}}-{{\phi }_{1}})}{5\,Rt}\] done clear
  C)
  \[-\frac{({{\phi }_{2}}-{{\phi }_{1}})}{\,Rnt}\]    done clear
  D)
  \[-\frac{n({{\phi }_{2}}-{{\phi }_{1}})}{\,Rt}\] done clear
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• question_answer5)
  A conducting disc of conductivity a has a radius 'a' and thickness 'f. If the magnetic field B is applied in a direction perpendicular to the plane of the disc changes with time at the rate of \[\frac{dB}{dt}=\alpha \]. Calculate the power dissipated in the disc due to the induced current.
  A)
  \[\frac{\pi t\sigma {{a}^{4}}}{8}{{\alpha }^{2}}\] done clear
  B)
  \[\frac{\pi t\sigma {{a}^{4}}}{4}{{\alpha }^{2}}\] done clear
  C)
  \[\frac{\pi t\sigma {{a}^{4}}}{2}{{\alpha }^{2}}\] done clear
  D)
  \[\frac{2\pi t\sigma {{a}^{4}}}{3}{{\alpha }^{2}}\] done clear
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• question_answer6)
  Shown in the figure is a circular loop of radius r and resistance R. A variable magnetic field of induction \[B={{B}_{0}}{{e}^{-t}}\]is established inside the coil. If the key (K) is closed, the electrical power developed right after closing the switch is equal to.                  
  A)
  \[\frac{B_{0}^{2}\pi {{r}^{2}}}{R}\] done clear
  B)
  \[\frac{{{B}_{0}}10{{r}^{3}}}{R}\] done clear
  C)
  \[\frac{B_{0}^{2}{{\pi }^{2}}{{r}^{4}}R}{5}\] done clear
  D)
  \[\frac{B_{0}^{2}{{\pi }^{2}}{{r}^{4}}}{R}\] done clear
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• question_answer7)
  A conductor AB of length\[l\]moves in x - y plane with velocity \[\vec{v}={{v}_{0}}(\hat{i}-\hat{j})\]. A magnetic field \[\overset{\to }{\mathop{B}}\,={{B}_{0}}(\hat{i}+\hat{j})\] exists in the region. The iduced Emf is
  A)
  zero done clear
  B)
  \[{{B}_{0}}l{{v}_{0}}\] done clear
  C)
  \[{{B}_{0}}l{{v}_{0}}\] done clear
  D)
  \[\sqrt{2}{{B}_{0}}1{{v}_{0}}\] done clear
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• question_answer8)

  A current carrying infinitely long wire is kept along the diameter of a circular wire loop, without touching it, the correct statement(s) is(are)

  I. The emf induced in the loop is zero if the current is constant.

  II. The emf induced in the loop is finite if the current is constant.

  III. The emf induced in the loop is zero if the current decreases at a steady rate.

  A)
  I only      done clear
  B)
        II only done clear
  C)
  I and II           done clear
  D)
         I, II and III done clear
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• question_answer9)
  Two different wire loops are concentric and lie in the same plane. The current in the outer loop (I) is clockwise and increases with time. The induced current in the inner loop    
  A)
  is clockwise          done clear
  B)
         is zero                  done clear
  C)
  is counter clockwise     done clear
  D)
  has a direction that depends on the ratio of the   loop radii. done clear
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• question_answer10)
  Fig shown below represents an area \[A=0.5\,{{m}^{2}}\] situated in a uniform magnetic field \[B=2.0\,weber/{{m}^{2}}\] and making an angle of \[60{}^\circ \] with respect to magnetic field.               The value of the magnetic flux through the area would be equal to
  A)
  2.0 weber           done clear
  B)
  \[\sqrt{3}\text{ }weber~~~\] done clear
  C)
  \[\sqrt{3}\text{/2 }weber\]           done clear
  D)
  0.5 weber done clear
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• question_answer11)
  In the figure the flux through the loop perpendicular to the plane of the coil and directed into the paper is varying according to the relation \[\phi =6{{t}^{2}}+7t+1\] where \[\phi \] is in milli weber and t is in second. The magnitude of the emf induced in the loop at t=2 s and the direction of induce current through R are                 
  A)
  39 m V; right to left       done clear
  B)
  39 m V; left to right       done clear
  C)
  31 m V; right to left      done clear
  D)
  31 m V; left to right       done clear
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• question_answer12)
  Magnetic flux linked with a stationary loop of resistance R varies with respect to time during the time period T as follows: \[\phi =at(T-t)\] The amount of heat generated in the loop during that time (inductance of the coil is negligible) is
  A)
  \[\frac{aT}{3R}\]           done clear
  B)
  \[\frac{{{a}^{2}}{{T}^{2}}}{3R}\] done clear
  C)
  \[\frac{{{a}^{2}}{{T}^{2}}}{R}\]      done clear
  D)
  \[\frac{{{a}^{2}}{{T}^{3}}}{3R}\] done clear
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• question_answer13)
  A conducting circular loop is placed in a uniform magnetic field of 0.04 T with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at 2 mm/s. The induced emf in the loop when the radius is 2 cm is
  A)
  \[4.8\pi \mu \,V\] done clear
  B)
  \[0.8\pi \mu \,V\] done clear
  C)
  \[1.6\pi \mu \,V\] done clear
  D)
  \[3.2\pi \mu \,V\] done clear
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• question_answer14)
  In a uniform and constant magnetic field of induction B, two long conducting wires ab and cd are kept parallel to each other at distance \[\ell \] with their plane perpendicular to B. The ends a and c are connected together by an ideal inductor of inductance L. A conducting slider wire PQ is imparted a speed \[{{v}_{0}}\] at time t=0. The situation is shown in the figure. At time\[t=\frac{\pi \sqrt{ML}}{4\,B\ell }\], the value of current \[I\] through the wire PQ is (ignore any resistance, electrical as well as mechanical)
  A)
  \[\sqrt{\frac{mv_{0}^{2}}{L}}\]           done clear
  B)
  \[\sqrt{\frac{mv_{0}^{2}}{2L}}\] done clear
  C)
  \[\sqrt{\frac{mv_{0}^{2}}{4L}}\]          done clear
  D)
  zero done clear
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• question_answer15)
  The figure shows a conducting loop consisting of half circle of area \[A=0.06\,{{m}^{2}}\] and three straight segments. The half circle lies in a uniform changing magnetic field \[B=4{{r}^{2}}+2t+5\] (SI unit), where t is the time in second. An ideal battery E=2V is connected as shown and the total resistance of the wire is \[2\Omega \]. The net current in the loop is at t=5 second is:
  A)
  1A  done clear
  B)
  1.5A            done clear
  C)
  0.26A done clear
  D)
  0.10A       done clear
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• question_answer16)
  A square loop with 2.0 m sides is perpendicular to a uniform magnetic field, with half the area of the loop in the field is shown in figure. The loop contains a 20.0 V battery with negligible internal resistance. If the magnitude of the field varies with time according to B = 0.042-0.871, with B in tesia and t in second. The net emf of the circuit is:
  A)
  \[20.0\,V\] done clear
  B)
  \[18.26\,V\] done clear
  C)
  \[21.74\,V\] done clear
  D)
  None of these done clear
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• question_answer17)
  A coil of circular cross-section having 1000 turns and\[4\,c{{m}^{2}}\] face area is placed with its axis parallel to a magnetic field which decreases by\[{{10}^{-2}}\,Wb\,\,{{m}^{-2}}\]  in 0.01 s. The e.m.f. induced in the coil is:
  A)
  400mV done clear
  B)
  200mV done clear
  C)
  4mV done clear
  D)
  0.4mV done clear
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• question_answer18)
  The radius of the circular conducting loop shown in fig. is R. Magnetic field is decreasing at a constant rate a. Resistance per unit length of the loop is \[\rho \]. Then, the current in wire AB is (AB is one of the diameters)
  A)
  \[\frac{R\alpha }{2\rho }\]from A to B done clear
  B)
  \[\frac{R\alpha }{2\rho }\] from B to A done clear
  C)
  \[\frac{R\alpha }{2\rho }\] from A to B done clear
  D)
  0 done clear
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• question_answer19)
  An equilateral triangular loop ABC made of uniform thin wires is being pulled out of a region with a uniform speed v, where a uniform magnetic field \[\vec{B}\] perpendicular to the plane of the loop exists. At time t=0, the point A is at the edge of the magnetic field. The induced current (I) vs time (t) graph will be as   
  A)
          done clear
  B)
  done clear
  C)
  done clear
  D)
  done clear
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• question_answer20)
  A vertical ring of radius r and resistance R falls vertically. It is in contact with two vertical rails which are joined at the top. The rails are without friction and resistance. There is a horizontal uniform magnetic field of magnitude B perpendicular to the plane of the ring and -the rails. When the speed of the ring is v, the current in the top horizontal of the rail section is
  A)
  0          done clear
  B)
  \[\frac{2Brv}{R}\]          done clear
  C)
  \[\frac{4Brv}{R}\]          done clear
  D)
  \[\frac{8Brv}{R}\] done clear
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• question_answer21)
  A flexible wire loop in the shape of a circle has radius that grown linearly with time. There is a magnetic field perpendicular to the plane of the loop that has a magnitude inversely proportional to the distance from the center of the loop, \[B(r)\propto \frac{1}{r}\].How does the emf E vary with time?
  A)
  \[E\propto {{t}^{2}}\]   done clear
  B)
  \[E\propto t\] done clear
  C)
  \[E\propto \sqrt{t}\]         done clear
  D)
  E is constant done clear
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• question_answer22)
  Charge Q is uniformly distributed on a thin insulating ring of mass m which is initially at rest. To what angular velocity will the ring be accelerated when a magnetic field B, perpendicular to the plane of the ring, is switched on?
  A)
  \[\frac{QB}{2m}\]          done clear
  B)
  \[\frac{3QB}{2m}\] done clear
  C)
  \[\frac{QB}{m}\]           done clear
  D)
  \[\frac{QB}{4m}\]   done clear
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• question_answer23)
  A rectangular coil has a long straight wire passing through its centroid perpendicular to its plane as shown. If current through the wire varies as \[i={{i}_{0}}\sin \omega t\], induced current in the coil will be (Given R = Resistance of the coil)     
  A)
  \[\frac{{{i}_{0}}\sin \omega t}{R}\]        done clear
  B)
  \[\frac{\pi a\sin \omega t}{bR}\] done clear
  C)
  zero done clear
  D)
  \[\frac{\pi a\cos \omega t}{bR}\] done clear
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• question_answer24)
  Two identical cycle wheels (geometrically) have different number of spokes connected from center to rim. One is having 20 spokes and the other having only 10 (the rim and the spokes are resistance less). One resistance of value R is connected between center and rim. The current in R will be
  A)
  double in the first wheel than in the second wheel done clear
  B)
  four times in the first wheel than in the second wheel done clear
  C)
  will be double in the second wheel than that of the first wheel done clear
  D)
  will be equal in both these wheels done clear
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• question_answer25)
  The magnetic field in a region is given by \[B={{B}_{0}}\left( 1+\frac{x}{a} \right)\hat{k}\]. A square loop of edge-length d is placed with its edges along the x and y-axes. The loop is moved with a constant velocity\[v={{v}_{0}}\hat{i}.\]The emf induced in the loop is:
  A)
  zero       done clear
  B)
  \[{{v}_{0}}{{B}_{0}}d\] done clear
  C)
  \[\frac{{{v}_{0}}{{B}_{0}}{{d}^{3}}}{{{a}^{2}}}\] done clear
  D)
  \[\frac{{{v}_{0}}{{B}_{0}}{{d}^{2}}}{a}\] done clear
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• question_answer26)
  A sliding wire of length 0.25 m and having a resistance of \[0.5\Omega \] moves along conducting guiding rails AB and CD with a uniform speed of 4 m/s. A magnetic field of 0.5 T exists normal to the plane of ABCD directed into the page. The guides are short -circuited with resistances of 4 and \[2\,\Omega \] as shown. The current through the sliding wire is:              
  A)
  0.27 A   done clear
  B)
  0.37 A done clear
  C)
  1.0 A    done clear
  D)
  0.72A done clear
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• question_answer27)
  An L-shaped conductor rod is moving in transverse magnetic field as shown in the figure. Potential difference between ends of the rod is maximum if the rod is moving with velocity
  A)
  \[4\hat{i}-6\hat{j}\,m/s\] done clear
  B)
  \[-\,4\hat{i}+6\hat{j}\,m/s\] done clear
  C)
  \[3\hat{i}+2\hat{j}\,m/s\] done clear
  D)
         \[\sqrt{13}\hat{i}\,m/s\] done clear
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• question_answer28)
  A conducting rod of mass m and \[\ell \]is placed on a smooth horizontal surface in a region where transverse uniform magnetic field B exists in the region. At t=0, constant force .F starts acting on the rod at its mid-point as shown. Potential difference between ends of the rod, \[{{V}_{p}}-{{V}_{Q}}\] at any time t is     
  A)
  \[\frac{BF\ell t}{2m}\] done clear
  B)
  \[\frac{BF\ell t}{4m}\] done clear
  C)
  \[\frac{5BF\ell t}{8m}\] done clear
  D)
  \[\frac{7BF\ell t}{8m}\] done clear
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• question_answer29)
  A thin circular ring of area A is perpendicular to uniform magnetic field of induction B. A small cut is made in the ring and a galvanometer is connected across the ends such that the total resistance of circuit is R. When the ring is suddenly squeezed to zero area, the charge flowing through the galvanometer is
  A)
  \[\frac{BR}{A}\] done clear
  B)
  \[\frac{AB}{R}\] done clear
  C)
  ABR done clear
  D)
  \[{{B}^{2}}\,A/{{R}^{2}}\] done clear
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• question_answer30)
  A 0.1 m long conductor carrying a current of 50 I A is perpendicular to a magnetic field of 1.21 mT. The mechanical power to move the conductor 1 with a speed of \[1\,m{{s}^{-1}}\] is                     
  A)
  0.25 m W  done clear
  B)
  6.25 m W           done clear
  C)
  0.625 W  done clear
  D)
  1W done clear
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• question_answer31)
  A wire is bent to form the double loop shown in Fig. There is a uniform magnetic field directed into the plane of the loop. If the magnitude of this field is decreasing, the current will flow from
  A)
  a to b and c to d done clear
  B)
  b to a and d to c  done clear
  C)
  a to b and d to c  done clear
  D)
  b to a and c to d  done clear
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• question_answer32)
  A conducting wire xy of length\[l\]and mass m is sliding without friction on vertical conduction rails ab and cd shown in Fig. A uniform magnetic field B exists perpendicular to the plane of the rails, x moves with a constant velocity of  
  A)
  \[\frac{mgR}{Bl}\] done clear
  B)
  \[\frac{mgR}{B{{l}^{2}}}\] done clear
  C)
  \[\frac{mgR}{{{B}^{2}}{{l}^{2}}}\] done clear
  D)
  \[\frac{mgR}{{{B}^{2}}l}\] done clear
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• question_answer33)
  A wooden stick of length \[3\ell \]is rotated about an end with constant angular velocity \[\omega \] in a uniform magnetic field B perpendicular to the plane of motion. If the upper one third of its length is coated with copper, the potential difference across the whole length of the stick is
  A)
  \[\frac{9B\omega {{\ell }^{2}}}{2}\] done clear
  B)
  \[\frac{4B\omega {{\ell }^{2}}}{2}\] done clear
  C)
  \[\frac{5B\omega {{\ell }^{2}}}{2}\] done clear
  D)
  \[\frac{B\omega {{\ell }^{2}}}{2}\] done clear
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• question_answer34)
  A uniform magnetic field of induction B is confined to a cylindrical region of radius R. The magnetic field is increasing at a constant rate of \[\frac{dB}{dt}\] (tesla/second). An electron of charge q, placed at the point P on the periphery of the field experiences an acceleration.
  A)
  \[\frac{BR}{(\sqrt{2}+1)m}\] towards left done clear
  B)
  \[\frac{1}{2}\,\frac{eR}{m}\,\frac{dB}{dt}\] towards left done clear
  C)
  \[\frac{eR}{m}\frac{dB}{dt}\] towards left done clear
  D)
  zero done clear
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• question_answer35)
  An equilateral triangular loop having a resistance R and length of each side\[\ell \]is placed in magnetic field which is varying at \[\frac{dB}{dt}=1\,T/s\]. The induced current in the loop will be       
  A)
  \[\frac{\sqrt{3}}{4}\frac{{{\ell }^{2}}}{R}\] done clear
  B)
         \[\frac{4}{\sqrt{3}}\frac{{{\ell }^{2}}}{R}\] done clear
  C)
  \[\frac{\sqrt{3}}{4}\,\frac{R}{{{\ell }^{2}}}\]    done clear
  D)
  \[\frac{4}{\sqrt{3}}\frac{R}{{{\ell }^{2}}}\] done clear
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• question_answer36)
  A copper rod of length 0.19 m is moving parallel to a long wire with a uniform velocity of 10 m/s. The long wire carries 5 ampere current and is perpendicular to the rod. The ends of the rod are at distances 0.01 m and 0.2 m from the wire. The emf induced in the rod will be-
  A)
  \[10\,\mu V\] done clear
  B)
  \[20\,\mu V\] done clear
  C)
  \[30\,\mu V\]      done clear
  D)
  \[40\,\mu V\] done clear
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• question_answer37)
  A metallic square loop ABCD is moving in its own plane with velocity v in a uniform magnetic field perpendicular to its plane as shown in the figure. An electric field is induced
  A)
  in AD, but not in BC done clear
  B)
  in BC, but not in AD done clear
  C)
  neither in AD nor in BC done clear
  D)
  in both AD and BC   done clear
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• question_answer38)
  A conducting wire of mass m slides down two smooth conducting bars, set at an angle 0 to the horizintal as shown in Fig. The separation between the bars is\[l\]. The system is located in the magnetic field B, perpendicular to the plane of the sliding wire and bars. The constant velocity of the wire is   
  A)
  \[\frac{mg\,R\,\sin \theta }{{{B}^{2}}{{l}^{2}}}\] done clear
  B)
  \[\frac{mg\,R\,\sin \theta }{B{{l}^{2}}}\] done clear
  C)
  \[\frac{mg\,R\,\sin \theta }{{{B}^{2}}{{l}^{5}}}\] done clear
  D)
  \[\frac{mg\,R\,\sin \theta }{B{{l}^{4}}}\] done clear
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• question_answer39)
  A plane loop, shaped as two squares of sides a =1 m and b=0.4 m is introduced into a uniform magnetic field\[\bot \]to the plane of loop. The magnetic field varies as \[B={{10}^{-3}}\sin \](100t) T. The amplitude of the current induced in the loop if its resistance per unit length is\[r=5\,m{{\Omega }^{-1}}\]is
  A)
  2 A done clear
  B)
    3 A done clear
  C)
  4 A done clear
  D)
  5 A    done clear
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• question_answer40)
  PQ is an infinite current carrying conductor. AB and CD are smooth conducting rods on which a conductor EF moves with constant velocity v as shown. The force needed to maintain constant speed of EF is        
  A)
  \[\frac{1}{vR}{{\left[ \frac{{{\mu }_{0}}Iv}{2\pi }In\,\left( \frac{b}{a} \right) \right]}^{2}}\] done clear
  B)
  \[{{\left[ \frac{{{\mu }_{0}}Iv}{2\pi }In\left( \frac{a}{b} \right) \right]}^{2}}\frac{1}{vR}\] done clear
  C)
  \[{{\left[ \frac{{{\mu }_{0}}Iv}{2\pi }In\left( \frac{b}{a} \right) \right]}^{2}}\frac{v}{R}\] done clear
  D)
  \[\frac{v}{R}{{\left[ \frac{{{\mu }_{0}}Iv}{2\pi }In\left( \frac{a}{b} \right) \right]}^{2}}\] done clear
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• question_answer41)
  A coil of resistance 400Q is placed in a magnetic field. If the magnetic flux \[\phi \] (wb) linked with the coil varies with time t (sec) as\[\phi =50{{t}^{2}}+4\]. The current in the coil at t=2 sec is:
  A)
  0.5 A done clear
  B)
  0.1 A done clear
  C)
  2 A    done clear
  D)
  1 A done clear
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• question_answer42)
  A straight conducting metal wire is bent in the given shape and the loop is closed. Dimensions are as shown in the figure. Now the assembly is heated at a constant rate \[~dT/dt\text{ }=\text{ }l{}^\circ C/s\]. The assembly is kept in a uniform magnetic field B=1 T, perpendicular into the paper. Find the current in the loop at the moment, when the heating starts. Resistance of the loop is \[10\Omega \] at any temperature. Coefficient of linear expansion \[\alpha ={{10}^{-6}}/{}^{o}C\].    
  A)
  \[1.5\times {{10}^{-6}}\,A\] anticlockwise   done clear
  B)
  \[1.5\times {{10}^{-6}}\,A\]clockwise   done clear
  C)
  \[0.75\times {{10}^{-6}}\,A\] anticlockwise done clear
  D)
  \[0.75\times {{10}^{-6}}\,A\]clockwise done clear
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• question_answer43)
  A rectangular coil of 20 turns and area of cross- section 25 sq. cm has a resistance of\[100\,\Omega \]. If a magnetic field which is perpendicular to the plane of coil changes at a rate of 1000 tesla per second, the current in the coil is
  A)
  1 A   done clear
  B)
  50 A done clear
  C)
  0.5 A done clear
  D)
  5 A done clear
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• question_answer44)
  A rectangular loop PQRS, is pulled with constant speed into a uniform transverse magnetic field by a force F (as shown). E.m.f. induced in side PS and potential difference between points P and S respectively are (Resistance of the loop = r)
  A)
  zero, \[\frac{Fr}{B\ell }\] done clear
  B)
  zero, zero done clear
  C)
  zero, \[\frac{Fr}{6B\ell }\] done clear
  D)
  \[\frac{Fr}{6B\ell },\,\frac{Fr}{6B\ell }\] done clear
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• question_answer45)
  A horizontal ring of radius \[r=\frac{1}{2}m\] is kept in a vertical constant magnetic field 1 T. The ring is collapsed from maximum area to zero area in 1 s. Then the emf induced in the ring is
  A)
  1 V  done clear
  B)
  \[(\pi /4)V\] done clear
  C)
  \[(\pi /2)V\] done clear
  D)
  \[\pi \,V\] done clear
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• question_answer46)
  A conducting rod of length l is hinged at point O. It is free to rotate in vertical plane. There exists a uniform magnetic field \[\vec{B}\]in horizontal direction. The rod is released from position shown in the figure. When rod makes an angle \[\theta \] from released position then potential difference between two ends of the rod is proportional to:         
  A)
  \[{{l}^{1/2}}\]                    done clear
  B)
  The lower end will be at a lower potential    done clear
  C)
  \[\sin \theta \] done clear
  D)
  \[{{\left( \sin \theta  \right)}^{1/2}}\] done clear
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• question_answer47)
  An aluminium ring hangs vertically from a thread with its axis pointing east - west. A coil is fixed near to the ring and coaxial with it. What is the initial motion of the aluminium ring when the current in the coil is switched on?
  A)
  moves toward E  done clear
  B)
  moves toward W done clear
  C)
  moves toward N done clear
  D)
  moves toward S done clear
  View Solution play_arrow

• question_answer48)
  A resistance less ring has 2 bulbs A and B rated at 2V, 19 W and 2V, 29 W respectively. The ring encloses an ideal solenoid whose magnetic field is as shown. The radius of solenoid is 1 m and the number of turns/length =1000/m. The current changes at rate of 9 A/sec Find the value of P if power dissipated in bulb B is \[180{}^\circ \] watt.       
  A)
  4      done clear
  B)
  6             done clear
  C)
  8          done clear
  D)
  11     done clear
  View Solution play_arrow

• question_answer49)
  A cylindrical region of radius 1 m has instantaneous homogenous magnetic field of 5T and it is increasing at a rate of 2T/s. A regular hexagonal loop ABCDEFA of side 1 m is being drawn in to the region with a constant speed of 1 m/s as shown in the figure. What is the magnitude of emf developed in the loop just after the shown instant when the corner A of the hexagon is coinciding with the centre of the circle?         
  A)
  \[5/\sqrt{3}V\] done clear
  B)
  \[2\pi /\sqrt{3}V\] done clear
  C)
  \[(5\sqrt{3}+2\pi /3)\,V\] done clear
  D)
  \[(5\sqrt{3}+\pi )\,V\] done clear
  View Solution play_arrow

• question_answer50)
               A thin semicircular conducting ring (PQR) of radius 'r' is falling with its plane vertical in a horizontal magnetic field B, as shown in figure. The potential difference developed across thering when its speed is v, is:  
  A)
  Zero            done clear
  B)
  \[Bv\pi {{r}^{2}}/2\] and P is at higher potential    done clear
  C)
  \[\pi rBv\] and R is at higher potential done clear
  D)
  2rBv and R is at higher potential done clear
  View Solution play_arrow

• question_answer51)
  A conducting square frame of side' a' and a long staight wire carrying current I are located in the same plane as shown in the figure. The frame moves to the right with a constant velocity ?V?. The emf induced in the frame will be proportional to
  A)
  \[\frac{1}{{{(2x-a)}^{2}}}\] done clear
  B)
  \[\frac{1}{{{(2x+a)}^{2}}}\] done clear
  C)
  \[\frac{1}{(2x-a)(2x+a)}\] done clear
  D)
  \[\frac{1}{{{x}^{2}}}\] done clear
  View Solution play_arrow

• question_answer52)
  The approximate formula expressing the formula of mutual inductance of two thin coaxial loops of the same radius a when their centers are separated by a distance \[l\] with \[l\] >>a is
  A)
  \[\frac{1}{2}\,\frac{{{\mu }_{0}}\pi {{a}^{4}}}{{{l}^{3}}}\] done clear
  B)
  \[\frac{1}{2}\,\frac{{{\mu }_{0}}\pi {{a}^{4}}}{{{l}^{2}}}\] done clear
  C)
  \[\frac{{{\mu }_{0}}}{4\pi }\frac{\pi {{a}^{4}}}{{{l}^{2}}}\] done clear
  D)
  \[\frac{{{\mu }_{0}}}{\pi }\frac{{{a}^{4}}}{{{l}^{3}}}\] done clear
  View Solution play_arrow

• question_answer53)
    A bar magnet was pulled away from a hollow coil A as shown in fig. As the South Pole came out of the coil, the bar magnet next to hollow coil B experienced a magnetic force
  A)
  to the right done clear
  B)
  to the left done clear
  C)
  upward done clear
  D)
  equal to zero done clear
  View Solution play_arrow

• question_answer54)
  A superconducting loop of radius R has self-inductance L. A uniform and constant magnetic field B is applied perpendicular to the plane of the loop. Initially current in this loop is zero. The loop is rotated by \[180{}^\circ \]. The current in the loop after rotation is equal to 
  A)
  zero done clear
  B)
  \[\frac{B\pi {{R}^{2}}}{L}\] done clear
  C)
  \[\frac{2B\pi {{R}^{2}}}{L}\] done clear
  D)
  \[\frac{B\pi {{R}^{2}}}{2L}\] done clear
  View Solution play_arrow

• question_answer55)
  Two inductances \[{{L}_{1}}\] and \[{{L}_{2}}\]are placed closer and in parallel. Their combined inductance is
  A)
  \[\frac{{{L}_{1}}{{L}_{2}}}{{{L}_{1}}+{{L}_{2}}}\] done clear
  B)
  \[({{L}_{1}}+{{L}_{2}})\] done clear
  C)
  \[({{L}_{1}}+{{L}_{2}})\,\frac{{{L}_{1}}}{{{L}_{2}}}\] done clear
  D)
  \[({{L}_{1}}+{{L}_{2}})\,\frac{{{L}_{2}}}{{{L}_{1}}}\]   done clear
  View Solution play_arrow

• question_answer56)
  Two coils are at fixed locations. Which coil 1 has no current and the current in coil 2 increases at the rate of \[15.0\,A\,{{s}^{-1}}\], the emf in coil 1 is 25 mV, when coil 2 has no current and coil 1 has a current of 3.6 A, the flux linkage on coil 2 is
  A)
  16 m Wb done clear
  B)
  10 m Wb done clear
  C)
  4.00 m Wb done clear
  D)
  6.00 m Wb done clear
  View Solution play_arrow

• question_answer57)
  What is the self-inductance of a coil which produces 5V when the current changes from 3 ampere to 2 ampere in one millisecond?
  A)
  5000 henry done clear
  B)
  5 milli-henry done clear
  C)
  50 henry done clear
  D)
  5 henry done clear
  View Solution play_arrow

• question_answer58)
  Figure shows a rectangular coil near a long wire. The mutual inductance of the combination is
  A)
  \[\frac{{{\mu }_{0}}a}{2\pi }ln\left( 1-\frac{b}{c} \right)\] done clear
  B)
  \[\frac{{{\mu }_{0}}a}{2\pi }ln\left( 1+\frac{b}{c} \right)\] done clear
  C)
  \[\frac{{{\mu }_{0}}a}{\pi }ln\left( 1+\frac{b}{c} \right)\] done clear
  D)
  \[\frac{{{\mu }_{0}}a}{\sqrt{2}\pi }ln\left( 1+\frac{b}{c} \right)\] done clear
  View Solution play_arrow

• question_answer59)
  In an inductor of self-inductance L=2mH, current changes with time according to relation \[i={{t}^{2}}{{e}^{-t}}\]. At what time emf is zero?
  A)
  4s done clear
  B)
  3s    done clear
  C)
  2s done clear
  D)
  Is done clear
  View Solution play_arrow

• question_answer60)
  A varying current in a coil changes from 10A to zero in 0.5 sec. If the average e.m.f induced in the coil is 220V, the self-inductance of the coil is
  A)
  5 H done clear
  B)
  6 H   done clear
  C)
  11 H done clear
  D)
  12 H done clear
  View Solution play_arrow

• question_answer61)
  A current of 1.5 A flows through a solenoid of length 20.0 cm, cross-section \[20.0\text{ }c{{m}^{2}}\] and 400 turns. The current is suddenly switched off in a short time of 1.0 millisecond. Ignoring the variation in the magnetic field the ends, the average back emf induced in the solenoid is:
  A)
  0.3 V    done clear
  B)
  9.6 V done clear
  C)
  30.0 V   done clear
  D)
  3.0 V done clear
  View Solution play_arrow

• question_answer62)
  Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be      
  A)
  maximum in situation [a] done clear
  B)
  maximum in situation [b] done clear
  C)
  maximum in situation [c] done clear
  D)
  the same in all situations done clear
  View Solution play_arrow

• question_answer63)
    A small square loop of wire of side \[\ell \] is placed inside a large square loop of wire of side \[L(L>\ell )\].The loop are coplanar and their centre coincide. The mutual inductance of the system is proportional to
  A)
  \[\ell /L\] done clear
  B)
  \[{{\ell }^{2}}/L\] done clear
  C)
  \[L/\ell \] done clear
  D)
  \[{{L}^{2}}/\ell \] done clear
  View Solution play_arrow

• question_answer64)
  Two coils, one primary of 500 turns and one secondary of 25 turns, are wound on an iron ring of mean diameter 20 cm and cross-sectional area\[12\,c{{m}^{2}}\]. If the permeability of iron is 800, the mutual inductance is:
  A)
  0.48 H done clear
  B)
  2.4 H done clear
  C)
  0.12 H done clear
  D)
  0.24 H done clear
  View Solution play_arrow

• question_answer65)
  When the current in a certain inductor coil is 5.0 A and is increasing at the rate of 10.0 A/s, the potential difference across the coil is 140V. When the current is 5.0 A and decreasing at the rate of 10.0 A/s, the potential difference is 60V. The self-inductance of the coil is -  
  A)
  2H        done clear
  B)
  4H   done clear
  C)
  8H        done clear
  D)
  12H done clear
  View Solution play_arrow

• question_answer66)
  A wire of fixed lengths is wound on a solenoid of length \[\ell \] and radius r. Its self-inductance is found to be L. Now if same wire is wound on a solenoid of length \[\ell /2\] and radius r/2, then the self in- ductance will be -
  A)
  2L        done clear
  B)
  L     done clear
  C)
  4L        done clear
  D)
  8L done clear
  View Solution play_arrow

• question_answer67)
  A rectangular loop has a sliding connector PQ of length \[\ell \] and resistance \[R\,\Omega \] and it is moving with a speed v as shown. The set-up is placed in a uniform magnetic field going m to the plane of the paper. The three currents \[{{I}_{1}},\,{{I}_{2}}\] and / are
  A)
  \[{{I}_{1}}=-{{I}_{2}}=\frac{Blv}{6R},\,I=\frac{2Blv}{6R}\] done clear
  B)
  \[{{I}_{1}}={{I}_{2}}=\frac{Blv}{3R},\,I=\frac{2Blv}{3R}\] done clear
  C)
  \[{{I}_{1}}={{I}_{2}}=I=\frac{Blv}{R}\] done clear
  D)
  \[{{I}_{1}}={{I}_{2}}=\frac{Blv}{6R}\], \[I=\frac{Blv}{3R}\] done clear
  View Solution play_arrow

• question_answer68)
  A boat is moving due east in a region where the earth's magnetic field is \[5.0\times {{10}^{-5}}N{{A}^{-1}}\,{{m}^{-1}}\] due north and horizontal. The boat carries a vertical aerial 2 m long. If the speed of the boat is\[1.50\,m{{s}^{-1}}\], the magnitude of the induced emf in the wire of aerial is                
  A)
  0.75 mV done clear
  B)
  0.50 mV done clear
  C)
  0.15 mV done clear
  D)
  1 mV done clear
  View Solution play_arrow

• question_answer69)
  A horizontal straight wire 20m long extending from east to west falling with a speed of 5.0 m/s, at right angles to the horizontal component of the earth's magnetic field \[0.30\times {{10}^{-4}}\,Wb/{{m}^{2}}\]. The instantaneous value of the e.m.f. induced in the wire will be
  A)
  3 mV done clear
  B)
  4.5 mV done clear
  C)
  1.5mV done clear
  D)
  6.0 mV done clear
  View Solution play_arrow

• question_answer70)
  A coil is suspended in a uniform magnetic field, with the plane of the coil parallel to the magnetic lines of force. When a current is passed through the coil it starts oscillating; It is very difficult to stop. But if an aluminium plate is placed near to the coil, it stops. This is due to:
  A)
  developement of air current when the plate is placed done clear
  B)
  induction of electrical charge on the plate done clear
  C)
  shielding of magnetic lines of force as aluminium is a paramagnetic material. done clear
  D)
  electromagnetic induction in the aluminium plate giving rise to electromagnetic damping. done clear
  View Solution play_arrow

• question_answer71)
  A long solenoid has 500 turns. When a current of 2 ampere is passed through it, the resulting magnetic flux linked with each turn of the solenoid is \[4\times {{10}^{-3}}\,Wb\]. The self- inductance of the solenoid is
  A)
  2.5 henry done clear
  B)
  2.0 henry done clear
  C)
  1.0 henry done clear
  D)
  40 henry done clear
  View Solution play_arrow

• question_answer72)
  A circular coil is radius 5 cm has 500 turns of a wire. The approximate value of the coefficient of self-induction of the coil will be-
  A)
  \[25\text{ }mH\] done clear
  B)
  \[25\times {{10}^{-3}}\,mH\] done clear
  C)
  \[50\times {{10}^{-3}}\,mH\] done clear
  D)
  \[50\times {{10}^{-3}}\,H\] done clear
  View Solution play_arrow

• question_answer73)
  A uniform coil of self-inductance \[1.8\times {{10}^{-4}}\,H\] and resistance 6W is broken up into two identical coils. These two coils are then connected in parallel across a 12 V battery. The circuit time constant and steady state current through the battery respectively are:
  A)
  \[30\text{ }\mu s,\text{ }8\text{ }A\] done clear
  B)
  30ms, 8mA done clear
  C)
  30s, 8 A done clear
  D)
  300s, 800 A done clear
  View Solution play_arrow

• question_answer74)
  The back e.m.f. in a d.c. motor is maximum, when
  A)
  the motor has picked up max speed done clear
  B)
  the motor has just started moving done clear
  C)
  the speed of motor is still on the increase done clear
  D)
  the motor has just been switched off done clear
  View Solution play_arrow

• question_answer75)
  A motor having an armature of resistance \[2\Omega \]. Is designed to operate at 220 V mains. At full speed, it develops a back emf of 210V. When the motor is running at full speed, the current in the armature is:
  A)
  3 A   done clear
  B)
  5 A   done clear
  C)
  7A   done clear
  D)
  10A done clear
  View Solution play_arrow

• question_answer76)
  A simple electric motor has an armature resistance of \[1\Omega ~\] and runs from a dc source of 12 volt. When running unloaded it draws a current of 2 amp. When a certain load is connected, its speed becomes one-half of its unloaded value. What is the new value of current drawn?
  A)
  7 A       done clear
  B)
  3 A    done clear
  C)
  5 A       done clear
  D)
  4 A done clear
  View Solution play_arrow

• question_answer77)
  When a metallic plate swings between the poles of a magnet
  A)
  no effect on the plate done clear
  B)
  eddy currents are set up inside the plate and the direction of the current is along the motion of the plate done clear
  C)
  eddy currents are set up inside the plate and the direction of the current opposes the motion of the plate done clear
  D)
  eddy currents are set up inside the plate done clear
  View Solution play_arrow

• question_answer78)
  An electric potential difference will be induced between the ends of the conductor as shown in the diagram, when the conductor moves in the direction           
  A)
  P done clear
  B)
  Q done clear
  C)
  L done clear
  D)
  M done clear
  View Solution play_arrow

• question_answer79)
  A rectangular coil of 200 turns of wire \[15\times 40\,c{{m}^{2}}\] makes 50 r.p.s. about an axis in its plane parallel to its longer side and perpendicular to a magnetic field of intensity \[0.08\,Wb/{{m}^{2}}\]. what is the instantaneous value of induced e.m.f. when the plane of the coil makes an angle with magnetic field of \[45{}^\circ \].
  A)
  213.3 V done clear
  B)
  301.7 V done clear
  C)
  151.5 V done clear
  D)
  zero done clear
  View Solution play_arrow

• question_answer80)
  A generator has an e.m.f. of 440 Volt and internal resistance of 4000 hm. Its terminals are connected to a load of 4000 ohm. The voltage across the load is
  A)
  220 volt done clear
  B)
  440 volt done clear
  C)
  200 volt done clear
  D)
  400 volt done clear
  View Solution play_arrow

• question_answer81)
  A metallic rod of length T is tied to a string of length U and made to rotate with angular speed co on a horizontal table with one end of the string fixed. If there is a vertical magnetic field 'B' in the region, the e.m.f. induced across the ends of the rod is       
  A)
  \[\frac{2B\omega {{\ell }^{2}}}{2}\] done clear
  B)
  \[\frac{3B\omega {{\ell }^{2}}}{2}\] done clear
  C)
  \[\frac{4B\omega {{\ell }^{2}}}{2}\] done clear
  D)
  \[\frac{5B\omega {{\ell }^{2}}}{2}\] done clear
  View Solution play_arrow

• question_answer82)
  A circular loop of radius 0.3 cm lies parallel to a much bigger circular loop of radius 20 cm. The centre of the small loop is on the axis of the bigger loop. The distance between their centres is 15 cm. If a current of 2.0 A flows through the smaller loop, then the flux linked with bigger loop is
  A)
  \[9.1\times {{10}^{-11}}\,weber\] done clear
  B)
  \[6\times {{10}^{-11}}\,weber\] done clear
  C)
  \[3.3\times {{10}^{-11}}\,weber\] done clear
  D)
  \[6.6\times {{10}^{-9}}\,weber\] done clear
  View Solution play_arrow

• question_answer83)
  In a coil of resistance 100 Q, a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is      
  A)
  250 Wb             done clear
  B)
  275 Wb   done clear
  C)
  200 Wb             done clear
  D)
  225 Wb                done clear
  View Solution play_arrow

• question_answer84)
  A charge Q is uniformly distributed over the surface of non-conducting disc of radius R. The disc rotates about an axis perpendicular to its plane and passing through its centre with an angular velocity co. As a result of this rotation a magnetic field of induction B is obtained at the centre of the disc. If we keep both the amount of charge placed on the disc and its angular velocity to be constant and vary the radius of the disc then the variation of the magnetic induction at the centre of the disc will be represented by the figure:
  A)
  done clear
  B)
  done clear
  C)
  done clear
  D)
  done clear
  View Solution play_arrow

• question_answer85)
  The two rails of a railway track, insulated from each other and the ground, are connected to a milli voltmeter. What is the reading of the milli voltmeter when a train travels at a speed of 180 km/hour along the track, given that the vertical component of earth's magnetic field is\[0.2\times {{10}^{-4}}\,weber/{{m}^{2}}\] and the rails are separated by 1 m?
  A)
  1 done clear
  B)
  3     done clear
  C)
  5 done clear
  D)
  7 done clear
  View Solution play_arrow

• question_answer86)
  A square metal wire loop of side 10 cm and resistance 1 ohm is moved with a constant velocity \[{{v}_{0}}\] in a uniform magnetic field of induction \[B=2\,weber/{{m}^{2}}\] as shown in the figure. The magnetic field lines are perpendicular to the plane of the loop (directed into the paper). The loop is connected to a network of resistors each of value 3 ohms. The resistances of the lead wires OS and PQ are negligible. What should be the speed of the loop so as to have a steady current of 1 milliampere in the loop? Give the direction of current in the loop.      
  A)
  2.3 m/s done clear
  B)
  1.2 m/s done clear
  C)
  0.3 m/s done clear
  D)
  0.02 m/s done clear
  View Solution play_arrow

• question_answer87)
  A conducting ring of radius r with a conducting spoke OA is in pure rolling on a horizontal surface in a region having a uniform magnetic field B as shown, v being the velocity of the centre of the ring. Then the potential difference \[{{V}_{0}}-{{V}_{A}}\]is:
  A)
  \[\frac{Bvr}{2}\] done clear
  B)
  \[\frac{3Bvr}{2}\] done clear
  C)
  \[\frac{Bvr}{2}\] done clear
  D)
  \[\frac{-3Bvr}{2}\] done clear
  View Solution play_arrow

• question_answer88)
             The figure below depicts a circular loop of radius R carrying a fixed current I. The upper half of the loop is placed in a uniform magnetic field of magnitude B, perpendicular to the plane of the paper, as shown. The magnitude of the force on the loop is (neglect gravity)
  A)
  BIR done clear
  B)
  2BIR done clear
  C)
  \[\pi BIR\] done clear
  D)
  \[2\pi BIR\] done clear
  View Solution play_arrow

• question_answer89)
  Two identical circular current carrying coils 1 and 2, each of radius R are placed adjacently a distance d apart (d<<R). They carry equal currents/in opposite sense. Let \[{{L}_{1}},\,{{L}_{2}},\,{{M}_{12}}\] and\[{{M}_{21}}\] denote the self and mutual inductances. Which of the following is at least approximately true?
  A)
  \[\left| \left. {{L}_{1}} \right| \right.=\left| \left. {{M}_{21}} \right| \right.\] done clear
  B)
  \[{{M}_{21}}>{{L}_{1}}\] done clear
  C)
  \[{{L}_{1}}=-{{L}_{2}}\] done clear
  D)
  \[{{M}_{12}}=-{{M}_{21}}\] done clear
  View Solution play_arrow

• question_answer90)
  An infinitesimally small bar magnet of dipole moment \[\vec{M}\] is pointing and moving with the speed v in the \[\hat{x}\]- direction. A small closed circular conducting loop of radius a and negligible self- inductance lies in the y-z plane with its center at x = 0, and its axis coinciding with the x-axis. Find the force opposing the motion of the magnet, if the resistance of the loop is R. Assume that the distance x of the magnet from the center of the loop is much greater than a.
  A)
  \[\frac{21}{4}\frac{\mu _{0}^{2}{{M}^{2}}{{a}^{4}}v}{R{{x}^{8}}}\]      done clear
  B)
  \[\frac{16}{3}\frac{{{\mu }_{0}}{{M}^{2}}{{a}^{2}}{{v}^{2}}}{R{{x}^{3}}}\] done clear
  C)
  \[\frac{3}{23}\frac{{{\mu }_{0}}Ma{{v}^{2}}}{R{{x}^{3}}}\]           done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer91)
  ABCD is a wire frame in the shape of an isosceles trapezium (i.e., length AB = length CD) enter a magnetic field with flux density B at t=0 as shown in the figure. If the total resistance of wire frame is R. What is the value of the induced current in the wire frame after t seconds, assuming that the frame has to entered the field completely by then? [v=Velocity of frame]
  A)
  zero done clear
  B)
  \[\frac{Bv}{R}(2vt\,\sin \,\theta +\ell )\] done clear
  C)
  \[\frac{Bv}{R}\left( \frac{2vt\,}{\tan \,\theta }+\ell  \right)\] done clear
  D)
  \[\frac{B}{v}\] done clear
  View Solution play_arrow

• question_answer92)
  The magnetic flux \[\phi \] linked with a conducting coil depends on time as \[\phi =4{{t}^{n}}+6\], where n is a positive constant. The induced emf in the coil is e. Then which is wrong?
  A)
  If \[0<n<1\], \[e\ne 0\] and \[\left. \left| e \right. \right|\]decreases with time done clear
  B)
  If n=1, e is constant done clear
  C)
  If n > 1, \[\left| e \right|\]increases with time done clear
  D)
  If n>l, \[\left| e \right|\] decreases with time done clear
  View Solution play_arrow

• question_answer93)
  A uniform circular loop of radius a and resistance R is placed perpendicular to a uniform magnetic field B. One half of the loop is rotated about the diameter with angular velocity\[\omega \]as shown in Fig. Then, the current in the loop is
  A)
  \[\frac{\pi {{a}^{2}}B\omega }{4R}\], when \[\theta \] is zero done clear
  B)
  \[\frac{\pi {{a}^{2}}B\omega }{2R}\], when \[\theta \] is zero done clear
  C)
  zero, when \[\theta =\pi /2\] done clear
  D)
  \[\frac{\pi {{a}^{2}}B\omega }{2R}\], when \[\theta =\pi /2\] done clear
  View Solution play_arrow

• question_answer94)
  A metal rod moves at a constant velocity in a direction perpendicular to its length. A constant, uniform magnetic field exists in space in a direction perpendicular to the rod as well as its velocity. Select the correct statement from the following.
  A)
  The entire rod is at the same electric potential. done clear
  B)
  There is an electric field in the rod. done clear
  C)
  The electric potential is highest at the centre of the rod and decreases towards its ends. done clear
  D)
  The electric potential is lowest at the centre of the rod, and increases towards its ends done clear
  View Solution play_arrow

• question_answer95)
  A nonconducting ring of mass m and radius R has a charge Q uniformly distributed over its circumference. The ring is placed on a rough horizontal surface such that the plane of the ring is parallel to the surface. A vertical magnetic field \[B={{B}_{0}}{{t}^{2}}\] tesla is switched on. After 2 second from switching on the magnetic field the ring is just about to rotate about vertical axis through its centre. Then
  A)
  the induced electric field is quadratic in time t done clear
  B)
  the force tangential to the ring is\[9{{B}_{0}}QRt\] done clear
  C)
  until 2 seconds, the friction force does not come into play done clear
  D)
  the friction coefficient between the ring and the surface is \[\frac{2{{B}_{0}}RQ}{mg}\]. done clear
  View Solution play_arrow

• question_answer96)
  There are three wire MO, NO and PQ, wires MO and NO are fixed and perpendicular to each other. Wire PQ moves with a constant velocity v as shown in the figure and resistance per unit length of each wire is\[\lambda \]and magnetic field exists   perpendicular and inside the paper then. Which of the following is wrong?
  A)
  current in loop is anticlockwise done clear
  B)
  magnitude of current in the loop is\[\frac{Bv}{\lambda (\sqrt{2}+1)}\] done clear
  C)
  current in the loop is independent of time. done clear
  D)
  magnitude of current decreases as time increases. done clear
  View Solution play_arrow

• question_answer97)
  A (current versus time) graph of the current passing through a solenoid is shown in figure. If the back emf at t=3s is e, find the back emf at t = 7 s      
  A)
  \[e/2\] done clear
  B)
  0 done clear
  C)
  \[\frac{-e}{2}\] done clear
  D)
  \[-3e\] done clear
  View Solution play_arrow

• question_answer98)
  The incorrect statements is/are
  A)
  The resistance offered by an inductor in a d. c circuit is always constant. done clear
  B)
  The resistance of inductor in steady state is zero. done clear
  C)
  An inductor is connected to a battery through a switch. The emf induced in the inductor is much larger when the switch is opened as compared to the emf induced when the switch is closed. done clear
  D)
  To reduce the rate of increases of current through a solenoid should increase the time constant\[\left( \frac{L}{R} \right)\]. done clear
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• question_answer99)
  In a conducting cycle wheel (of n spokes), each spoke of length fi is rotating with angular speed \[\omega \] in uniform perpendicular magnetic field B. If due to flux cutting each metal spoke behaves as an identical cell of emf(e) then net emf of the system is             
  A)
  \[nB\omega {{l}^{2}}\] done clear
  B)
  \[\frac{1}{2}nB\omega {{l}^{2}}\] done clear
  C)
  \[\frac{1}{2}B\omega {{l}^{2}}\] done clear
  D)
  \[B\omega {{l}^{2}}\] done clear
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• question_answer100)
  A rod OA of length \[l\] is rotating (about end 0)  over a conducting ring in crossed magnetic field B with constant angular velocity co as shown in  figure
  A)
  Current flowing through the rod is\[\frac{B\omega \,{{l}^{2}}}{R}\] done clear
  B)
  Magnetic force acting on the rod is \[\frac{3{{B}^{2}}\omega \,{{l}^{3}}}{4R}\] done clear
  C)
  Torque due to magnetic force acting on the rod is\[\frac{3{{B}^{2}}\omega \,{{l}^{4}}}{8R}\] done clear
  D)
  Magnitude of external force that acts perpendicularly at the end of the rod to maintain the constant angular speed is \[\frac{3{{B}^{2}}\omega \,{{l}^{3}}}{5R}\].             done clear
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