-
question_answer1)
Direction: Q.1 to Q.5 |
The induced electromotive force with different polarities induces a current whose magnetic field opposes the change in magnetic flux through the loop in order to ensure that original flux is maintained through the loop when current flows in it. |
To batter understand Lenz's law, let us consider two cases: |
Case 1: When a magnet is moving towards the coil. |
|
When the north pole of the magnet is approaching towards the coil, the magnetic flux linking to the coil increases. According to Faraday's law of electromagnetic induction, when there is a change in flux, an emf, and hence current is induced in the coil and this current will create its own magnetic field. |
Now according to Lenz's law, this magnetic field created will oppose its own or we can say opposes the increase in flux through the coil and this is possible only if approaching coil side attains north polarity, as we know similar poles repel each other. Once we know the magnetic polarity of the coil side, we can easily determine the direction of the induced current by applying right hand rule. In this case, the current flows in the anticlockwise direction. |
Case 2: When a magnet is moving away from the coil |
|
When the north pole of the magnet is moving away from the coil, the magnetic flux linking to the coil decreases. According to Faraday's law of electromagnetic induction, an emf and hence current is induced in the coil and this current will create its own magnetic field. |
Now according to Lenz's law, this magnetic field created will oppose its own or we can say opposes the decrease in flux through the coil and this is possible only if approaching coil side attains south polarity, as we know dissimilar poles attract each other. Once we know the magnetic polarity of the coil side, we can easily determine the direction of the induced current by applying right hand rule. In this case, the current flows in a clockwise direction. |
Read the above passage carefully and give the answer of the following questions: |
What is the direction of the induced magnetic field?
A)
left done
clear
B)
right done
clear
C)
up done
clear
D)
down done
clear
View Solution play_arrow
-
question_answer2)
What is the direction of the induced magnetic field? Magnet moving up
A)
left done
clear
B)
right done
clear
C)
up done
clear
D)
down done
clear
View Solution play_arrow
-
question_answer3)
In what direction is the magnet moving?
A)
left done
clear
B)
right done
clear
C)
cup done
clear
D)
down done
clear
View Solution play_arrow
-
question_answer4)
In what direction is the magnet moving?
A)
left done
clear
B)
right done
clear
C)
cup done
clear
D)
down done
clear
View Solution play_arrow
-
question_answer5)
Which of the following is NOT an application of Lenz's Law
A)
Transformer done
clear
B)
AC Generator done
clear
C)
DC Motor done
clear
D)
A coil transversed by AC current done
clear
View Solution play_arrow
-
question_answer6)
Direction: Q.6 to Q.10 |
Lenz's law states that the direction of induced current in a circuit is such that it opposes the change which produces it. Thus, if the magnetic flux linked with a closed circuit increases, the induced current flows in such a direction that a magnetic flux is created in the opposite direction of the original magnetic flux. If the magnetic flux linked with the closed circuit decreases, the induced current flows in such a direction so as to create a magnetic flux in the direction of the original flux. |
|
Read the above passage carefully and give the answer of the following questions: |
Which of the following statement is correct?
A)
The 'induced emf is not in the direction opposing the change in magnetic flux so as to oppose the cause which produces it. done
clear
B)
The relative motion between the coil and magnet produces change in magnetic flux. done
clear
C)
emf is induced only if the magnet is moved towards coil. done
clear
D)
emf is induced only if the coil is moved towards magnet. done
clear
View Solution play_arrow
-
question_answer7)
The polarity of induced emf is given by:
A)
Ampere's circuital law done
clear
B)
Biot-Savart law done
clear
C)
Lenz's law done
clear
D)
Fleming's right hand rule done
clear
View Solution play_arrow
-
question_answer8)
Lenz's law is a consequence of the law of conservation of
A)
charge done
clear
B)
mass done
clear
C)
momentum done
clear
D)
energy done
clear
View Solution play_arrow
-
question_answer9)
Near a circular Loop of conducting wire as shown in the figure, an electron moves along a straight line. The direction of the induced current if any in the loop is:
A)
variable done
clear
B)
clockwise done
clear
C)
anticlockwise done
clear
D)
zero done
clear
View Solution play_arrow
-
question_answer10)
Two identical circular coils A and B are kept in a horizontal tube side by side without touching each other. If the current in the coil A increases with time, in response, the coil B:
A)
is attracted by A done
clear
B)
remains stationary done
clear
C)
is repelled done
clear
D)
rotates done
clear
View Solution play_arrow
-
question_answer11)
Direction: Q.11 to Q.15 |
The emf induced across the ends of a conductor |
due to its motion in a magnetic field is called motional emf. It is produced due to the magnetic |
|
Lorentz force acting on the free electrons of the conductor. For a circuit shown in figure, if a conductor of length l moves with velocity v in a magnetic field B perpendicular to both its length and the direction of the magnetic field, then all the induced parameters are possible in the circuit. |
Read the above passage carefully and give the answer of the following questions: |
Direction of current induced in a wire moving in a magnetic field is found using:
A)
Fleming's left hand rule done
clear
B)
Fleming's right hand rule done
clear
C)
Ampere's rule done
clear
D)
Right hand clasp rule done
clear
View Solution play_arrow
-
question_answer12)
A conducting rod of length l is moving in a transverse magnetic field of strength B with velocity v. The resistance of the rod is R. The current in the rod is:
A)
\[\frac{Blv}{R}\] done
clear
B)
\[Blv\] done
clear
C)
zero done
clear
D)
\[\frac{{{B}^{2}}{{v}^{2}}{{l}^{2}}}{R}\] done
clear
View Solution play_arrow
-
question_answer13)
A 0.1 m long conductor carrying a current of 50A is held perpendicular to a magnetic field of 1.25 mT. The mechanical power required to move the conductor with a speed of \[1\text{ }m{{s}^{-1}}\] is:
A)
62.5 mW done
clear
B)
625 mW done
clear
C)
6.25 mW done
clear
D)
12.5 mW done
clear
View Solution play_arrow
-
question_answer14)
A bicycle generator creates 1.5 V at 15 km/hr. The EMF generated at 10 km/hr is:
A)
1.5 volts done
clear
B)
2 volts done
clear
C)
0.5 volts done
clear
D)
1 volt done
clear
View Solution play_arrow
-
question_answer15)
The dimensional formula for emf \[\varepsilon \] in MKS system will be:
A)
\[[M{{L}^{2}}{{T}^{-3}}{{A}^{-1}}]\] done
clear
B)
\[[M{{L}^{2}}{{T}^{-1}}A]\] done
clear
C)
\[[M{{L}^{2}}A]\] done
clear
D)
\[[ML{{T}^{-2}}{{A}^{-2}}]\] done
clear
View Solution play_arrow
-
question_answer16)
Direction: Q.16 to Q.20 |
Current can be induced not only in conducting coils, but also in conducting sheets or blocks. Current is induced in solid metallic masses when the magnetic flux threading through them changes. Such currents flow in the form of irregularly shaped loops throughout the body of the metal. These currents look like eddies or whirlpools in water so they are known as eddy currents. Eddy currents have both undesirable effects and practically useful applications. For example, it causes unnecessary heating and wastage of power in electric motors, dynamos and in the cores of transformers. |
Read the given passage carefully and give the answer of the following questions: |
The working of speedometers of trains is based on:
A)
wattles currents done
clear
B)
eddy currents done
clear
C)
alternating currents done
clear
D)
pulsating currents done
clear
View Solution play_arrow
-
question_answer17)
Identify the wrong statement:
A)
Eddy currents are produced in a steady magnetic field. done
clear
B)
Induction furnace use eddy currents to produce heat. done
clear
C)
Eddy currents can be used to produce breaking force in moving trains. done
clear
D)
Power meters work on the principle of eddy currents. done
clear
View Solution play_arrow
-
question_answer18)
Which of the following is the best method to reduce eddy currents?
A)
Laminating core done
clear
B)
Using thick wires done
clear
C)
By reducing hysteresis loss done
clear
D)
None of these done
clear
View Solution play_arrow
-
question_answer19)
The direction of eddy currents is given by:
A)
Fleming's left hand rule done
clear
B)
Biot-Savart law done
clear
C)
Lenz's law done
clear
D)
Ampere circuital law done
clear
View Solution play_arrow
-
question_answer20)
Eddy currents can be used to heat localised tissues of the human body. This branch of medical therapy is called:
A)
Hyperthermia done
clear
B)
Diathermy done
clear
C)
Inductothermy done
clear
D)
none of these done
clear
View Solution play_arrow
-
question_answer21)
Direction: Q.21 to Q.25 |
An eddy current is a current set up in a conductor in response to a changing magnetic field. They flow in closed loops in plane perpendicular to the magnetic field. By Lenz's law, the current swirls in such a way as to create a magnetic field opposing the change; for this to occur in a conductor, electrons swirl in a plane perpendicular to the magnetic field. |
Because of the tendency of eddy currents to oppose, eddy currents cause a loss of energy. Eddy currents transform more useful forms of energy. Eddy currents can also be removed by cracks or slits in the conductor, which break the circuit and prevent the current loops from circulating. This means that eddy currents can be used to detect defects in materials. This is called non destructive testing and is often used in airplanes. The magnetic field produced by the eddy currents is measured, where a change in the field reveals the presence of an irregularity a defect will reduce the size of the eddy current, which in turn reduces the magnetic field strength. |
Another application of eddy currents is magnetic levitation. Conductors are exposed to varying magnetic fields which induce eddy currents within the conductor and produce a repulsive magnetic field, pushing the magnet and conductor apart. This alternating magnetic field can be caused by relative motion between the magnet and conductor (generally the magnet is stationary and the conductor moves) or with an electromagnet applied with a varying current to very the magnetic field strength. |
Read the above passage carefully and give the answer of the following questions: |
What is the heat generated in eddy current operations?
A)
\[Vl\] done
clear
B)
\[VlR\] done
clear
C)
\[{{l}^{2}}RT\] done
clear
D)
\[{{l}^{2}}R\] done
clear
View Solution play_arrow
-
question_answer22)
With an increase in the density of the material, the power loss in eddy current:
A)
increases done
clear
B)
decreases done
clear
C)
does not change done
clear
D)
not related done
clear
View Solution play_arrow
-
question_answer23)
Generation of eddy currents depends on the principle of:
A)
wave guide theory done
clear
B)
electromagnetic induction done
clear
C)
magneto-restrictive force done
clear
D)
All of the above done
clear
View Solution play_arrow
-
question_answer24)
Eddy currents generated in a test object flow:
A)
in the same plane as magnetic flux done
clear
B)
in the same plane as the coil is wound done
clear
C)
\[90{}^\circ \] to the coil winding plane done
clear
D)
Eddy currents have no predictable direction done
clear
View Solution play_arrow
-
question_answer25)
The discovery of electromagnetic induction is credited to:
A)
Arago done
clear
B)
Oersted done
clear
C)
Maxwell done
clear
D)
Faraday done
clear
View Solution play_arrow
-
question_answer26)
Direction: Q.26 to Q.30 |
Mutual inductance is the phenomenon of inducing emf in a coil, due to a charge of current in the neighbouring coil. The amount of mutual inductance that links one coil to another depends very much on the relative positioning of the two coils, their geometry and relative separation between them. Mutual inductance between the two coils increases \[{{\mu }_{r}}\] times if the coils are wound over an iron core of relative permeability\[{{\mu }_{r}}\]. |
|
Read the above passage carefully and give the answer of the following questions: |
A short solenoid of radius a, number of turns per unit length \[{{n}_{1}}\] and length L is kept coaxially inside a very long solenoid of radius b, number of turns per unit length \[{{n}_{2}}\]. What is the mutual inductance of the system?
A)
\[{{\mu }_{0}}\pi {{b}^{2}}{{n}_{1}}{{n}_{2}}L\] done
clear
B)
\[{{\mu }_{0}}\pi {{a}^{2}}{{n}_{1}}{{n}_{2}}{{L}^{2}}\] done
clear
C)
\[{{\mu }_{0}}\pi {{a}^{2}}{{n}_{1}}{{n}_{2}}L\] done
clear
D)
\[{{\mu }_{0}}\pi {{b}^{2}}{{n}_{1}}{{n}_{2}}{{L}^{2}}\] done
clear
View Solution play_arrow
-
question_answer27)
If a change in current of 0.01 A in one coil produces a change in magnetic flux of \[2\times {{10}^{-2}}\] weber in another coil, then the mutual inductance between coils is:
A)
0 done
clear
B)
0.5 H done
clear
C)
2 H done
clear
D)
3 H done
clear
View Solution play_arrow
-
question_answer28)
Mutual inductance of two coils can be increased by:
A)
decreasing the number of turns in the coils done
clear
B)
increasing the number of turns in the coils done
clear
C)
Winding the coils on wooden cores done
clear
D)
None of the above done
clear
View Solution play_arrow
-
question_answer29)
When a sheet of iron is placed in between the two co-axial coils, then the mutual inductance between the coils will:
A)
increase done
clear
B)
decrease done
clear
C)
remains same done
clear
D)
cannot be predicted done
clear
View Solution play_arrow
-
question_answer30)
The SI unit of mutual inductance is:
A)
ohm done
clear
B)
mho done
clear
C)
henry done
clear
D)
None of these done
clear
View Solution play_arrow
-
question_answer31)
Direction: Q.31 to Q.35 |
Mutual inductance between the two coils is defined as the property of the coil due to which it opposes the change of current in the other coil, or you can say in the neighbouring coil. When the current in the neighbouring coil changes, the flux sets up in the coil and because of this, changing flux emf is induced in the coil called mutually induced emf and the phenomenon is known as mutual inductance. |
|
The value of mutual inductance (M) depends upon the following factors: |
1. Number of turns in the secondary or neighbouring coil, |
2. Cross-sectional area, |
3. Closeness of the two coils. |
When on a magnetic core, two or more than two coils are wound, the coils are said to be mutually coupled. The current, when passed in any of the coils wound around the magnetic core, produces flux which links all the coils together and also the one in which current is passed. Hence, there will be both self-induced emf and mutual induced emf in each of the coils. The best example of the mutual inductance is the transformer, which works in the principle of Faraday's Law of Electromagnetic induction. |
Faraday's law of electromagnetic induction states that, "the magnitude of voltage is directly proportional to the rate of change of flux." |
Read the above passage carefully and give the answer of the following questions: |
The phenomenon due to which there is an induced current in one coil due to current in a neighbouring coil is?
A)
Electromagnetism done
clear
B)
Susceptance done
clear
C)
Mutual inductance done
clear
D)
Steady current done
clear
View Solution play_arrow
-
question_answer32)
Mutual inductance between two magnetically coupled coils depends on:
A)
permeability of the core material done
clear
B)
number of the turns of the coils done
clear
C)
cross sectional area of their common core done
clear
D)
All of the above done
clear
View Solution play_arrow
-
question_answer33)
Which of the following is unit of inductance?
A)
Ohm done
clear
B)
Henry done
clear
C)
Ampere done
clear
D)
Webers/meter done
clear
View Solution play_arrow
-
question_answer34)
Which of the following circuit elements will oppose the change in circuit current?
A)
Capacitance done
clear
B)
Inductance done
clear
C)
Resistance done
clear
D)
All of these done
clear
View Solution play_arrow
-
question_answer35)
If in an iron cored coil the iron core is removed so as to make the air cored coil, the inductance of the coil will be
A)
more done
clear
B)
less done
clear
C)
the same done
clear
D)
None of these done
clear
View Solution play_arrow
-
question_answer36)
Direction: Q.36 to Q.40 |
When a current I flows through a coil, flux linked with it is \[\phi =LI\], where L is a constant known as self inductance of the coil. Any change in current sets up an induced emf in the coil. Thus, self inductance of a coil is the induced emf set up in the coil when the current passing through it changes at the unit rate. It is a measure of the opposition to the growth or the decay of current flowing through the coil. Also, value of self inductance depends on the number of turns in the solenoid, its area of cross-section and the relative permeability of its core material. |
|
Read the above passage carefully and give the answer of the following questions: |
The inductance in a coil plays the same role as:
A)
inertia in mechanics done
clear
B)
energy in mechanics done
clear
C)
momentum in mechanics done
clear
D)
force in mechanics done
clear
View Solution play_arrow
-
question_answer37)
A current of 2.5 A flows through a coil of inductance 5H. The magnetic flux linked with the coil is:
A)
0.5 Wb done
clear
B)
12.5 Wb done
clear
C)
zero done
clear
D)
2 Wb done
clear
View Solution play_arrow
-
question_answer38)
The inductance L of a solenoid depends upon its radius R as:
A)
\[L\propto R\] done
clear
B)
\[L\propto l/R\] done
clear
C)
\[L\propto {{R}^{2}}\] done
clear
D)
\[L\propto {{R}^{3}}\] done
clear
View Solution play_arrow
-
question_answer39)
The unit of self-inductance is:
A)
weber ampere done
clear
B)
\[\text{webe}{{\text{r}}^{\text{-1}}}\text{ampere}\] done
clear
C)
ohm second done
clear
D)
farad done
clear
View Solution play_arrow
-
question_answer40)
The induced e.m.f. in a coil of 10 henry inductance in which current varies from 9 A to 4 A in 0.2 second is:
A)
200 V done
clear
B)
250 V done
clear
C)
300 V done
clear
D)
350 V done
clear
View Solution play_arrow