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# Test C - Electromagnetic Induction (EMI), Class 12 Physics Class 12 Notes | EduRev

## Class 12 : Test C - Electromagnetic Induction (EMI), Class 12 Physics Class 12 Notes | EduRev

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1. Give the direction in which induced current flows in the wire loop, when the magnet moves towards
the loop as shown. 
N        S
2. If the rate of change of current 2 ampere/second induces an emf of 40 mV in the solenoid, what is
the self-inductance of this solenoid ? 
3. Why does a metallic piece become very hot when it is surrounded by a coil carrying high frequency
alternating current ? 
4. A conducting rod AB is moving parallel to X-axis in a uniform magnetic field pointing along (+)
Z-axis (figure). Which end of rod will be positively charged ? 
X
5. Show that Lenz's law is in accordance with the law of conservation of energy. 
6. How is the mutual inductance of a pair of coils affected when
(i) separation between the coils is increased ?
(ii) the number of turns in each coil is increased ?
(iii) a thin iron sheet is placed between the two coils, other factors remaining the same ?
7. An air core solenoid is connected to an ac source and a bulb. If an iron core is inserted in the
solenoid, how does the brightness of the bulb change ? Give reason for your answer. 
8. A circular coil of N-turns and radius R, is kept normal to a magnetic field, given by B = B
0
cos ?t.
Deduce an expression for the emf induced in this coil. State the rule which helps to detect the
direction of induced current. 
9. Derive expression for self inductance of a long air-cored solenoid of length l, cross-sectional area
A and having number of turns N. 
10. Current in a circuit falls from 5.0 A to 0.0 A in 0.1 s. If an average emf of 200 V is induced. Calculate
the self-induction of the circuit. 
11. A circular coil of radius 8.0 cm and 20 turns is rotated about its vertical diameter with an angular
speed of 50 rad/s in a uniform horizontal magnetic field of magnitude 3.0 × 10
–2
T. Obtain the
maximum and average emd induced in the coil. If the coil forms a closed loop of resistance 10 ?,
calculate the maximum value of current in the coil. Calculate the average power loss due to joule
heating. Where does the power come from ? 
12. A long solenoid with 15 turns per cm has a small loop of area 2.0 cm
2
placed inside normal to the
axis of the solenoid. The current carried by the solenoid changes steadily from 2A to 4A in 0.1 s,
what is the induced emf in the loop while the current is changing ? 
13. An air cored solenoid with length 30 cm, area of cross-section 25 cm
2
and number of turns 500
carries a current of 2.5 A. The current is suddenly switched off in a brief time of 10
–3
s. How much
is the average back emf induced across the ends of the open switch in the circuit ? Ignore the
variation in magnetic field near the ends of the solenoid. 
ELECTROMAGNETIC INDUCTIONS T E S T - C
X I I
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