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

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1. What is the magnitude of the induced current in the circular loop KLMN of radius r, if the straight
wire PQ carries a steady current of magnitude I ampere ? [1]
P Q
M
N L
K
I
2. Two identical loops, one of copper and another of aluminium are rotated with the same speed in the
same magnetic field. In which case, the induced (a) e.m.f. (b) current will be more any why ? [1]
3. Why is spark produced in the switch of a fan, when it is switched off ? [1]
4. Define coefficient of mutual inductance for a pair of coils. [1]
5. A magnetic field of flux density 10 T acts normal to a coil of 50 turns having 100 cm
2
 area. Find
e.m.f. induced. If the coil is removed from the magnetic field of 0.1 s. [2]
6. How does the self inductance of a coil change when :
(i) the number of turns in the coil is decreased
(ii) an iron rod is introduced into it ? Justify you answer in each case. [2]
7. The magnetic flux through a coil perpendicular to its plane is varying according to the relation
? = (4t
3
 + 5t
2
 + 8t + 5) weber
Calculate the induced current through the coil at t = 2s, if the resistance of the coil is 3.2 ohm. [2]
8. A flat coil of 500 turns. each of area 50 cm
2
, rotates in a uniform magnetic field of 0.14 Wbm
–2
 at an
angular speed  of 150 rad s
–1
. The coil has a resistance of 5 ?. The induced e.m.f. is applied to an
external resistance of 10 ?. Calculate the peak current through the resistance. [2]
9. Show that the energy stored in an inductor L when a current I
0
 is established through it is
U = 
1
2
LI
0
2
. [2]
10. Show that Lenz's law is direct consequence of the law of conservation of energy. [2]
11. An aircraft with a wing span of 40 m flies with a speed of 1080 kmh
–1
 in the eastward direction at a
constant altitude in the northern hemisphere, where the vertical component of earth's magnetic field
is 1.75 × 10
–5
 T. Find the e.m.f. that develops between the tips of the wings.   [3]
12. A circular loop of radius 0.3 cm lies parallel to a much bigger circular loop of radius 20 cm. The
centre of the small loop is on the axis of the bigger loop. The distance between their centre is 15 cm.
15 cm
20 cm
0.3 cm
(a) What is the flux linking the bigger loop, if a current of 2.0 A flows through the smaller loop ?
(b) Obtain the mutual inductance of the two loops. [3]
13. Explain construction and working of an ac generator. [3]
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