A magnetic field of T acts at right angles
to a coil of area 100 , with 50 turns. The average
e.m.f. induced in the coil is 0.1 V, when it is removed
from the field in t sec. The value of t is
1
10 s
2
0.1 s
3
0.01 s
4
1 s
Official Solution
Correct Option: (2)
02
PYQ 1997
medium
physicsID: neet-ug-
The primary winding of a transformer has 500 turns
whereas its secondary has 5000 turns. The primary
is connected to an A.C. supply 20 V, 50 Hz. The
secondary will have an output of
1
2 V, 50 Hz
2
2 V, 5 Hz
3
200 V, 50 Hz
4
200 V, 500 Hz.
Official Solution
Correct Option: (3)
Turns on primary winding = 500; Turns on secondary winding = 5000; Primary winding voltage = 20 V and frequency = 50 Hz.
or and frequency remains the same. Therefore secondary winding will have an output of 200 V, 50 Hz. So, the correct answer is (C): 200 V, 50 Hz.
03
PYQ 2004
easy
physicsID: neet-ug-
A coil of 40 henry inductance is connected in series with a resistance of 8 ohms and the combination is joined to the terminals of a 2-volt battery. The time constant of the circuit is
1
seconds
2
40 seconds
3
20 seconds
4
5 seconds
Official Solution
Correct Option: (4)
τ=LR= =5 sec
04
PYQ 2004
medium
physicsID: neet-ug-
A galvanometer acting as a voltmeter will have
1
a high resistance in series with its coil
2
a low resistance in parallel with its coil
3
a low resistance in series with its coil
4
a high resistance in parallel with its coil
Official Solution
Correct Option: (1)
A galvanometer acting as a voltmeter will have a high resistance in series with its coil.
05
PYQ 2008
easy
physicsID: neet-ug-
A circular disc of radius 0.2 meter is placed in a uniform magnetic field of induction in such a way that its axis makes an angle of 60 with . The magnetic flux linked with the disc is
1
0.08 Wb
2
0.01 Wb
3
0.02 Wb
4
0.06 Wb
Official Solution
Correct Option: (3)
Area of the disc normal to B is p cos60 . Flux = B x Area normal
06
PYQ 2009
medium
physicsID: neet-ug-
A rectangular, a square, a circular and an elliptical loop, all in the plane, are
moving out of a uniform magnetic field with a constant velocity, . The magnetic field is directed along the negative z-axis direction. The induced emf, during the passage of these loops, come out of the field region, will not remain constant for:
1
the circular and the elliptical loops
2
only the elliptical loop
3
any of the four loops
4
the rectangular, circular and elliptical loops
Official Solution
Correct Option: (1)
Out of the four structures, when the circular and elliptical loops come out from the field, equal are is not traced in equal interval of time. So any induced in both is not constant.
07
PYQ 2009
easy
physicsID: neet-ug-
A conducting circular loop is placed in a uniform magnetic field with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at The induced emf in the loop when the radius is is
1
2
3
4
Official Solution
Correct Option: (4)
08
PYQ 2011
medium
physicsID: neet-ug-
In an ac circuit , an alternating voltage volts is connected to a capacitor of capacitance . The rms value of the current in the circuit is :
1
10 mA
2
100 mA
3
200 mA
4
20 mA
Official Solution
Correct Option: (4)
given
09
PYQ 2012
medium
physicsID: neet-ug-
In a coil of resistance 10 Ω, the induced current developed by changing magnetic flux through it, is shown in figure as a function of time. The magnitude of change in flux through the coil in weber is
1
8
2
2
3
6
4
4
Official Solution
Correct Option: (2)
Area under i-t graph = q q = ½ x 4 x 0.1 = 0.2 C As Δϕ = qR = (0.2 C)(10 Ω) So, Δϕ = 2 weber Hence, option B) 2 is the correct answer.
10
PYQ 2013
medium
physicsID: neet-ug-
A wire loop is rotated in magnetic field. The frequency of change of direction of the induced e.m.f. is :
1
Six times per revolution
2
Once per revolution
3
twice per revolution
4
four times per revolution
Official Solution
Correct Option: (3)
Consider the ring starting to rotate from its initial position where it is perpendicular to the magnetic field. Thus initially maximum flux is passing through the loop. When it rotates, the flux passing through the loop starts to decrease. When it becomes parallel to the magnetic field, the flux becomes zero and then starts to increase. Here the direction of the induced emf remains the same. Then as it rotates further, it keeps on increasing, reaches maximum. Here the direction of induced emf changes. According to lenz law, the induced emf tends to oppose the flux when it was increasing and now since it is decreasing, it tends to increase it.
11
PYQ 2014
medium
physicsID: neet-ug-
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 the ring when its speed is v, is:
1
and P is at higher potential
2
πrBv and R is at higher potential
3
2rBv and R is at higher potential
4
Zero
Official Solution
Correct Option: (3)
The correct option (C): 2rBv and R is at higher potential
12
PYQ 2014
medium
physicsID: neet-ug-
A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are:
1
450V, 15A
2
450V, 13.5A
3
600V, 15A
4
300V, 15A
Official Solution
Correct Option: (1)
The correct option (A): 450V, 15A
13
PYQ 2015
easy
physicsID: neet-ug-
An electron moves on a straight line path as shown. The abcd is a coil adjacent to the path of electron. What will be the direction of current, if any, induced in the coil?
1
The current will reverse its direction as the electron goes past the coil
2
No current induced
3
abcd
4
adcb
Official Solution
Correct Option: (1)
When the electron moves from X to X, the flux linked with the coil abed (which is into the page) will first increase and then decrease as the electron passes by. So the induced current in the coil will be first anticlockwise and will reverse its direction (z.e. will become clockwise) as the electron goes past the coil.
14
PYQ 2015
easy
physicsID: neet-ug-
A resistance 'R' draws power 'P' when connected to an AC source. If an inductance is now placed in series with the resistance, such that the impedance of the circuit becomes 'Z', the power drawn will be
1
2
3
4
Official Solution
Correct Option: (3)
Case I :
Case II : Power drawn in LR circuit
[Using eqn (i)]
15
PYQ 2016
easy
physicsID: neet-ug-
A long solenoid has turns. When a current of flows through it, the magnetic flux linked with each turn of the solenoid is . The self-inductance of the solenoid is :
1
3 H
2
2 H
3
1 H
4
4 H
Official Solution
Correct Option: (3)
Flux linked with each turn Total flux linked =
16
PYQ 2016
medium
physicsID: neet-ug-
A uniform magnetic field is restricted within a region of radius . The magnetic field changes with time at a rate . Loop of radius enclosed the region and loop of radius is outside the region of magnetic field as shown in the figure below. Then the e.m.f. generated is
1
Zero in loop and zero in loop
2
in loop and in loop
3
in loop and zero in loop
4
in loop and zero in loop
Official Solution
Correct Option: (4)
Induced Electromotive Force (e.m.f.) Calculation
Let's calculate the induced e.m.f. in two different loops based on the magnetic field changes.
Induced e.m.f. in Loop (1)
The induced e.m.f. in loop (1) is given by Faraday's law of induction:
Where: - is the induced e.m.f., - is the magnetic flux, - is the area of the loop, - is the magnetic field strength, and - is the rate of change of the magnetic field.
For a circular loop of radius , the area is given by . Substituting this into the equation, we get:
Induced e.m.f. in Loop (2)
For loop (2), which is not in the magnetic field, there is no change in the magnetic field through the loop. Since there is no change in magnetic flux, the induced e.m.f. is zero:
Conclusion:
Loop (1) experiences an induced e.m.f. based on the change in the magnetic field, while loop (2) does not experience any induced e.m.f. as it is not in the magnetic field.
17
PYQ 2017
hard
physicsID: neet-ug-
A long solenoid of diameter has turns per meter. At the centre of the solenoid, a coil of turns and radius is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to from in . If the resistance of the coil is . the total charge flowing through the coil during this time is :
1
2
3
4
Official Solution
Correct Option: (2)
Sol.
Putting values
18
PYQ 2018
medium
physicsID: neet-ug-
An inductor , a capacitor and a resistor are connected in series across a source of emf, . The power loss in the circuit is
1
1.13 W
2
0.79 W
3
2.74 W
4
0.43 W
Official Solution
Correct Option: (2)
19
PYQ 2019
medium
physicsID: neet-ug-
A cycle wheel of radius is rotated with constant angular velocity of in a region of magnetic field of which is perpendicular to the plane of the wheel. The generated between its centre and the rim is,
1
0.25 V
2
0.125 V
3
0.5 V
4
zero
Official Solution
Correct Option: (2)
The formula to calculate emf is
is the electromotive force (EMF) generated.
is the magnetic field strength (0.1 Tesla in this case).
is the length, 0.5m
ω is the angular velocity (10 radians per second).
To calculate the value of EMF, let's put the values in the formula:
20
PYQ 2019
medium
physicsID: neet-ug-
In which of the following devices, the eddy current effect is not used ?
1
electromagnet
2
electric heater
3
induction furnace
4
magnetic braking in train
Official Solution
Correct Option: (2)
Electric heater does not involve Eddy currents. It uses Joule's heating effect.
21
PYQ 2019
easy
physicsID: neet-ug-
A 800 turn coil of effective area 0.05 is kept perpendicular to a magnetic field T. When the plane of the coil is rotated by around any of its coplanar axis in 0.1 s, the emf induced in the coil will be
1
V
2
0.02 V
3
2V
4
0.2 V
Official Solution
Correct Option: (2)
Magnetic field Number of turns in coil N = 800 Area of coil A = 0.05 Time taken to rotate t = 0.1 s Initial angle Final angle Change in magnetic flux
= - NBA
= - 2 weder
22
PYQ 2021
hard
physicsID: neet-ug-
Two conducting circular loops of radii R1 and R2 are placed in the same plane with their centers coinciding. If R1 > > R2, the mutual inductance M between them will be directly proportional to
1
2
3
4
Official Solution
Correct Option: (1)
To determine the mutual inductance between two concentric loops with radii and where , we employ the formula for mutual inductance between two coaxial loops. The mutual inductance between such loops in the planar arrangement is largely influenced by the area of the smaller loop, and the magnetic field at the location of the smaller loop due to current in the larger loop.
The mutual inductance is given by:
This formula arises because the magnetic field produced by the larger loop at the center is , where is the current in the larger loop. The magnetic flux through the smaller loop (area ) is . The mutual inductance is the flux per unit current: .
This directly implies that the mutual inductance is directly proportional to , i.e., the ratio of the area of the smaller loop to the radius of the larger loop.
Let's rule out the other options:
: Implies the mutual inductance increases with the radius of the larger loop, which contradicts the formula since it actually contributes to the denominator.
: Correct in identifying the relation with radii but misses squaring the smaller loop radius's effect (area).
: Suggests incorrectly about dependence on the larger loop's squared radius.
Thus, the correct option is .
23
PYQ 2023
easy
physicsID: neet-ug-
The net magnetic flux through any closed surface is:
1
Negative
2
Zero
3
Positive
4
Infinity
Official Solution
Correct Option: (2)
According to Gauss's law for magnetism, the net magnetic flux through any closed surface is always zero. This is because magnetic field lines form closed loops and do not begin or end at any point, implying there are no magnetic monopoles. Mathematically, Gauss's law for magnetism is expressed as:
∊B · dA = 0
where ∊B represents the magnetic flux density and dA is a differential element of area on the closed surface. This equation indicates that the total amount of magnetic field lines entering the surface is equal to the amount leaving it, resulting in a net magnetic flux of zero.
Option
Explanation
Negative
Magnetic field lines do not have directionality that would result in a net negative flux.
Zero
As explained by Gauss's law for magnetism, the net flux is always zero.
Positive
There is no unidirectional field contribution in closed surfaces to result in a positive flux.
Infinity
Magnetic field lines do not accumulate to infinite flux in a closed surface.
Thus, the correct answer is: Zero
24
PYQ 2023
easy
physicsID: neet-ug-
The magnetic engery stored in an inductor of inductance 4μH carrying a current of 2 A is:
1
4μJ
2
4μJ
3
4mJ
4
8μJ
Official Solution
Correct Option: (4)
To calculate the magnetic energy stored in an inductor, we use the formula for energy stored in an inductor: where is the energy in joules, is the inductance in henries (H), and is the current in amperes (A).
Given that the inductance is 4μH (microhenries) and the current is 2 A, we convert 4μH to henries:
4μH = 4 × 10-6 H
Substitute these values into the formula:
Calculate the current squared:
2² = 4
Substitute back into the equation:
Therefore, the magnetic energy stored in the inductor is 8μJ (microjoules). The correct answer is 8μJ.
25
PYQ 2024
easy
physicsID: neet-ug-
A step up transformer is connected to an ac mains supply of 220 V to operate at 11000 V, 88 watt. The current in the secondary circuit, ignoring the power loss in the transformer, is
1
8 mA
2
4 mA
3
0.4 A
4
4 A
Official Solution
Correct Option: (1)
Ignoring power loss, power in primary = power in secondary. Power (P) = VI Primary voltage ( ) = 220 V Secondary voltage ( ) = 11000 V Power (P) = 88 W Secondary current ( ) = ?
88 = 11000
26
PYQ 2024
medium
physicsID: neet-ug-
Let us consider two solenoids A and B, made from same magnetic material of relative permeability and equal area of cross-section. Length of A is twice that of B and the number of turns per unit length in A is half that of B. The ratio of self inductances of the two solenoids, LA : LB is
1
1 : 2
2
2 : 1
3
8 : 1
4
1 : 8
Official Solution
Correct Option: (1)
Self-inductance (L) of a solenoid is proportional to n2l, where n is the number of turns per unit length and l is the length.
Given: LA = 2LB nA = nB Let LA and LB be the self-inductances of solenoids A and B respectively.
