Electromagnetic Induction Online Objective Test | Electromagnetic Induction Online Objective Test

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q1. If AC generator coil has area A, rotates in a magnetic field of B with an angular speed ω , the voltage generated is

A. varies quadratically

B. varies linearly

C. varies sinusoidally.

D. is constant

Answer : Option C
Explaination / Solution:

e=NBAωSinωt

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q2. A circular coil of radius 10 cm, 500 turns and resistance

2 Ω

is placed with its plane perpendicular to the horizontal component of the earth’s magnetic field. It is rotated about its vertical diameter through

18 0^{\circ}

in 0.25 s. Estimate the magnitudes of the emf and current induced in the coil. Horizontal component of the earth’s magnetic field at the place is

3 \times 10^{- 5} T

A. 3.8 mv, 1.9mA

B. 2 mv,1mA

C. 1 mv,2mA

D. 2 mv,2.5mA

Answer : Option A
Explaination / Solution:

$\begin{aligned} e = - N \frac{d ϕ}{d t} \\ e = - \frac{N B A (\cos θ_{2} - \cos θ_{1})}{d t} = - \frac{500 \times 3 \times 10^{- 5} \times 3.14 \times 10^{- 2} (\cos 180^{\circ} - \cos 0^{\circ})}{0.25} \\ e = 3.8 \times 10^{- 3} = 3.8 m V \end{aligned}$

$i = \frac{e}{R} = \frac{3.8}{2} = 1.9 m A$

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q3.

Figure shows planar loops of different shapes moving out of or into a region of a magnetic field which is directed normal to the plane of the loop away from the reader. Direction of induced current in i,ii and iii are

A. anti-clockwise, anti-clockwise, clockwise

B. clockwise, clockwise, clockwise

C. anti-clockwise, clockwise, anti-clockwise

D. anti-clockwise, clockwise, clockwise .

Answer : Option D
Explaination / Solution:

(i) Due to motion, the magnetic flux linked with the loop abcd increases. According to lenz's law this increase in flux is opposed by the induced current. Therefore, the induced current must flow anticlockwise

(ii) Due to motion, the magnetic flux linked with the loop abc decreases. So that induced current is clockwise.

(iii) Due to motion, the magnetic flux linked with the loop decreases. So that induced current is clockwise

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q4.

A rectangular loop and a circular loop are moving out of a uniform magnetic field region to a field-free region with a constant velocity v as shown in fig. In which loop do you except the induced EMF to be constant during the passage out of the field region if the field is normal to the loops.

A. Both of them

B. rectangular loop

C. none

D. circular loop

Answer : Option B
Explaination / Solution:

The induced EMF is expected to be constant in the case of a rectangular loop. In case of a circular loop, the rate of change of area of the loop during the passage out of the field region is not constant, whereas it is constant for rectangular loop.

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q5. Polarity of the capacitor in the situation described by the adjacent figure is

A. Both A and B will become negative

B. Both A and B will become positive

C. A will become positive with respect to B

D. A will become negative with respect to B

Answer : Option C
Explaination / Solution:

A will become positive with respect to B because current indused is in clockwise direction

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q6. Predict the polarity of the capacitor in the situation described by fig.

A. Not enough information

B. A’ will be positive with respect to plate ‘B’ .

C. No current induced

D. B’ will be positive with respect to plate ‘A’

Answer : Option B
Explaination / Solution:

A will become positive with respect to B because current indused is in clockwise direction

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q7. A metallic rod of 1 m length is rotated with a frequency of 50 rev/s about an axis passing through the centre point O. Other end of the metallic rod slides on a Metallic ring . A constant and uniform magnetic field of 2 T parallel to the axis is present everywhere. What is the emf between the centre and the metallic ring?

A. 220 V

B. 314 V .

C. 240 V

D. 300 V

Answer : Option B
Explaination / Solution:

B = 2T

n = 50 rev/sec

$ω = 2 π n$

l = 1m

$e = \frac{1}{2} B ω l^{2} = \frac{1}{2} \times 2 \times 2 \times 3.14 \times 50 \times 1 \times 1 = 314 V$

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q8. A wheel with 10 metallic spokes each 0.5 m long is rotated with a speed of 60 rev/min in a plane normal to the horizontal component of earth’s magnetic field HE at a place. If HE = 0.4 G at the place, what is the induced emf between the axle and the rim of the wheel? Note that 1 G = 10–4 T.

A. 2.24

\times 1 0^{- 5} V

B. 2.44

\times 1 0^{- 5} V

C. 3.00

\times 1 0^{- 5} V

D. 3.14

\times 1 0^{- 5} V

Answer : Option D
Explaination / Solution:

e=12Bωl2=12×0.4×10−4×2×3.14×1×0.5×0.5=3.14×10−5V

ω=2πn

n=60/60=1rev/sec

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q9. The arm PQ of the rectangular conductor is moved from

x = 0

, outwards. The uniform magnetic field is perpendicular to the plane and extends from

x = 0

x = b

and is zero for

x > b

. Only the arm PQ possesses substantial resistance r. Consider the situation when the arm PQ is pulled outwards from

x = 0

x = 2 b

,and is then moved back to

x = 0

with constant speed v. flux and emf for

b \leq x < 2 b

b \leq x < 2 b

A. Blx,-Bv

B. Blb, zero .

C. Bl,-Blv

D. Bx,-Blv

Answer : Option B
Explaination / Solution:

ϕ=Blb

E=−dϕdt=0

# Electromagnetic Induction # CBSE 12TH PHYSICS Prepare / Learn

Q10. Given magnetic field B, area A and length l of a solenoid. The magnetic energy per unit volume is

A. 12μ0B2A

B. 32μ0B2Al

C. B22μ0

D. 12μ0B3Al

Answer : Option C
Explaination / Solution:

U=12μ0B2Al

UV=B22μ0

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