# An inductance L and a resistance R are first connected to a battery. After some time the battery is disconnected but L and R remain connected in a closed circuit. Then the current reduces to 37% of its initial value in time ? (1) RL sec (2) $\frac{R}{L}sec$ (3) $\frac{L}{R}sec$ (4) $\frac{1}{LR}sec$

Subtopic:  LR circuit |
78%
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In an LR-circuit, the time constant is that time in which current grows from zero to the value (where I0 is the steady-state current)

(1) 0.63 I0

(2) 0.50 I0

(3) 0.37 I0

(4) I0

Subtopic:  LR circuit |
76%
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In the figure magnetic energy stored in the coil is

(1) Zero

(2) Infinite

(3) 25 joules

(4) None of the above

Subtopic:  Self - Inductance |
83%
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A copper rod of length l is rotated about one end perpendicular to the magnetic field B with constant angular velocity ω. The induced e.m.f. between the two ends is

(1) $\frac{1}{2}B\omega {l}^{2}$

(2) $\frac{3}{4}B\omega {l}^{2}$

(3) $B\omega {l}^{2}$

(4) $2B\omega {l}^{2}$

Subtopic:  Motional emf |
89%
From NCERT
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Two conducting circular loops of radii $$R_1$$ and $$R_2$$ are placed in the same plane with their centres coinciding. If $$R_1>>R_2$$, the mutual inductance $$M$$ between them will be directly proportional to:

 1 $$\dfrac{R_1}{R_2}$$ 2 $$\dfrac{R_2}{R_1}$$ 3 $$\dfrac{R^2_1}{R_2}$$ 4 $$\dfrac{R^2_2}{R_1}$$
Subtopic:  Mutual Inductance |
63%
From NCERT
NEET - 2021
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A thin semicircular conducting ring of radius $$R$$ is falling with its plane vertical in a horizontal magnetic induction $$B$$. At the position $$MNQ$$, the speed of the ring is $$v$$ and the potential difference developed across the ring is:

 1 Zero 2 $$B v \pi R^2 / 2$$ and $$M$$ is at the higher potential 3 $$2 R B v$$ and $$M$$ is at the higher potential 4 $$2RBv$$ and $$Q$$  is at the higher potential
Subtopic:  Motional emf |
65%
From NCERT
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Consider the situation shown in the figure. The wire AB is sliding on the fixed rails with a constant velocity. If the wire AB is replaced by semicircular wire, the magnitude of the induced current will

(1) Increase

(2) Remain the same

(3) Decrease

(4) Increase or decrease depending on whether the semicircle bulges towards the resistance or away from it

Subtopic:  Motional emf |
68%
From NCERT
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A circular loop of radius R carrying current I lies in the x-y plane with its centre at the origin. The total magnetic flux through the x-y plane is

(1) Directly proportional to I

(2) Directly proportional to R

(3) Directly proportional to R2

(4) Zero

Subtopic:  Magnetic Flux |
53%
From NCERT
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A small square loop of wire of side l is placed inside a large square loop of wire of side L (L > l). The loop are coplanar and their centre coincide. The mutual inductance of the system is proportional to

(1) l / L

(2) l2 / L

(3) L/l

(4) L2/l

Subtopic:  Mutual Inductance |
79%
From NCERT
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A uniform but time-varying magnetic field B(t) exists in a circular region of radius a and is directed into the plane of the paper, as shown. The magnitude of the induced electric field at point P at a distance r from the centre of the circular region

(1) Is zero

(2) Decreases as $\frac{1}{r}$

(3) Increases as r

(4) Decreases as $\frac{1}{{r}^{2}}$

Subtopic:  Faraday's Law & Lenz Law |
59%
From NCERT
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