Physics Chapter 9 Entry test MCQs
Topic 9
Electromagnetic Induction
1. A step-down transformer reduces the supply voltage from 220 V to 11V and increase the current from 6 A to 100 A. Then its efficiency is
a. 0.12
b. 1.2
c. 0.9
d. 0.83
2. In a transformer, the number of turns in the primary and the secondary are 40 and 1230 respectively. If the current in primary is 6A, then that in the secondary coil is
a. 12 A
b. 2 A
c. 1 A
d. 18 A
3. Which of the following will not generate emf?
a. Rotating a coil in a magnetic field
b. Holding a magnet stationary inside a coil
c. Moving a bar magnet across a flat piece of metal
d. Rotating a coil around a stationary coil
4. Which one of the following does not affect the magnitude of the induced emf in electromagnetic induction?
a. The resistance of the coil cutting the magnetic field
b. The strength of the magnetic field linking to the coil
c. The number of turns in the coil
d. The speed with which the coil cuts the magnetic field
5. Relative motion between a————and a conducting coil produces current in the coil
a. Iron bar
b. Magnet
c. Insulator
d. All of these
6. In a closed ring (a) and in an open ring (b) magnets are falling along the axis of the ring The current generated in a and b have directions
a. Clockwise, zero
b. Anticlockwise, clockwise
c. Anticlockwise, zero
d. Zero, Zero
7. The direction of induced current in a coil or circuit is such that it opposes every cause of its production. This law is given by
a. Kirchhoff
b. Faraday
c. Ampere
d. Lenz
8. A metallic circular ring is suspended by a string and is kept in a vertical plane. When Magnet is approached towards the ring then it will
a. Remain stationary
b. Get displaced towards the magnet
c. Get displaced away from the magnet
d. Nothing Can be said
9. In equation epsilon ε = – N Δɸ/Δt the negative sign indicates that
a. The accordance of equation with the Lenz’s Law
b. The self-induced opposes its cause
c. The induced e.m.f opposes the change which produces it.
d. All of the above
10. The e.m.f. induced in a coil is …… the rate of change in flux linkages.
a. Inversely proportional to
b. Directly proportional to
c. Independent of
d. None of the above
11. A coil having 500 square loops each of side 10 cm is placed normal to a magnetic induction which increases at the rate of 1.0 tesla/second. The induced e.m.f. in volts is
a. 0.1
b. 5
c. 0.5
d. 1
12. In a circuit with a coil of resistance 2 ohms, the magnetic flux changes from 2.0 Wb to 10.0 Wb in 0.2 second. The charge that flows in the coil during this time is
a. 4.0 coulomb
b. 5.0 coulomb
c. 0.8 coulomb
d. 1.0 coulomb
13. A magnet falls with its S-pole along the axis of ring. The current Generated is ……….. and acceleration is
a. Clockwise, > g
b. Anticlockwise, > g
c. Clockwise, < g
d. Anticlockwise, < g
14. Lenz’s law is a manifestation of the conservation of
a. Voltage
b. Energy
c. Current
d. All of these
15. When a coil of cross-sectional area A and number of turns N is rotated in a uniform magnetic field B with angular velocity 0, then the maximum emf induced in the coil will be
a. Baω/N
b. BNA
c. Zero
d. ΒΝΑω
16. The Graphs shows how an alternating current I of peak value Io varies with time t.
Which expression gives the alternating current I?
a. I= Io sin (5πt)
b. I= Io sin (πt/0.0025)
c. I= Io sin (2πt/2.5)
d. I= Io sin (800πt)
17. The diagram shows how the e.m.f of a simple generator varies with time. what is the frequency and the maximum value of the e.m.f?
| Frequency/ Hz | Maximum e.m.f/ V | |
| A | 200 | 2.0 |
| B | 200 | 4.0 |
| C | 400 | 2.0 |
| D | 400 | 4.0 |
18. An electric generator is a device that transforms———–energy into electrical energy
a. Mechanical
b. Sound
c. Magnetic
d. Heat
19. The output of an a.c. generator has a
a. Square shape
b. Sinusoidal shape
c. Straight line shape
d. Triangular shape
20. The principle of an electric generator is based on
a. Coulomb’s law
b. Faraday’s law
c. Lenz’s law
d. Ampere’s law
21. The armature of a generator consists of a flat square coil of side 4 cm and 200 turns. The coil rotates in a magnetic field of 0.75T. The angular speed so that a maximum emf of 1.6V is generated is
a. 20/3 rotations/s
b. 20/3 rads-1
c. 20/3 rpm
d. None
22. The Graph shows the variation with the time t of a low frequency alternating voltage V.
which expression is a representation of this voltage?
a. 0.5 sin(0.4πt)
b. 1.0 sin(0.2πt)
c. 0.5 sin(10πt)
d. 1.0 sin(10πt)
23. Which quantity is increased in step-down transformer?
a. Voltage
b. Current
c. Frequency
d. Power
24. Which of the remain constant in a transformer?
a. Power
b. Current
c. Frequency
d. Potential
25. The voltage in the primary and the secondary coils of a step-up transformer are 200 V and 4 kV respectively. If the current in the primary is 1 ampere, then the current in the secondary coil will be
a. 5A
b. 50 mA
c. 5 mA
d. 500 mA