Paper 1 Alternating Current Generators Drills

Q1

An ac generator converts

A. electrical energy to chemical energy.
B. mechanical energy to electrical energy.
C. thermal energy to rest mass.
D. capacitance to resistance.

Q2

A simple ac generator requires

A. a rotating coil in magnetic field.
B. a stationary charge only.
C. a capacitor only.
D. a diode only.

Q3

The induced emf in a rotating coil is due to changing

A. flux linkage.
B. resistance only.
C. temperature.
D. charge density only.

Q4

Slip rings in an ac generator

A. reverse connections every half-turn.
B. maintain connection to rotating coil while preserving alternating output.
C. smooth the output.
D. store charge.

Q5

For a coil rotating uniformly, magnetic flux varies approximately as

A. $\Phi =BA\cos \omega t$.
B. $\Phi =BA\omega t$.
C. $\Phi =0$ always.
D. $\Phi =B/A$.

Q6

The induced emf is maximum when rate of change of flux linkage is

A. zero.
B. maximum.
C. negative only.
D. equal to resistance.

Q7

If flux is maximum at an instant in a rotating coil, induced emf is

A. zero.
B. maximum.
C. infinite.
D. same as flux.

Q8

For $N$ turns, peak emf is proportional to

A. $NBA\omega$.
B. $N/(BA\omega )$.
C. $B/A$.
D. $I/R$.

Q9

Increasing rotation frequency of the coil

A. increases peak emf.
B. decreases peak emf.
C. does not affect frequency of output.
D. makes dc output.

Q10

The output frequency of a simple generator is linked to

A. rotation frequency.
B. coil resistance only.
C. load colour.
D. temperature only.

Q11

A commutator rather than slip rings is used in a simple dc generator to

A. reverse connections each half-turn.
B. remove magnetic field.
C. reduce flux to zero.
D. increase capacitance.

Q12

In an ac generator, emf reverses sign because

A. flux-linkage gradient reverses.
B. charge is destroyed.
C. field vanishes permanently.
D. resistance is negative.

Q13

A stronger magnetic field in the generator

A. increases peak emf.
B. decreases peak emf.
C. has no effect.
D. makes rms zero.

Q14

A larger coil area

A. increases flux amplitude.
B. decreases all flux.
C. reverses current only.
D. removes slip rings.

Q15

The emf waveform of an ideal uniformly rotating coil is

A. sinusoidal.
B. square always.
C. constant zero.
D. random.

Q16

The phase difference between flux and induced emf is

A. $90^{\circ }$ for sinusoidal rotation.
B. $0^{\circ }$ always.
C. $180^{\circ }$ always.
D. undefined because emf is dc.

Q17

At the position where the coil plane is perpendicular to the field, flux is

A. maximum magnitude.
B. zero.
C. changing fastest.
D. impossible.

Q18

At the position where the coil plane is parallel to the field, flux is

A. maximum.
B. zero.
C. constant forever.
D. equal to resistance.

Q19

Generator output can be increased by

A. more turns, stronger field, larger area or faster rotation.
B. lower speed only.
C. smaller area only.
D. removing the field.

Q20

The generated electrical power ultimately comes from

A. mechanical work done turning the coil.
B. free magnetic energy.
C. charge creation.
D. voltmeter reading.