JAMB Physics Past Questions & Answers - Page 388

1,936.

The d.c generator has essentially the same components as the a.c generator except the presence of?

A.

slip-ring

B.

carbon brushes

C.

split ring

D.

armature

Correct answer is C

To correct and A.C generator with a D.C generator the slip ring is replaced with split-ring communicator

1,937.

A generator is on daily use and in the process, ten 60 W and five 40 W tungsten bulbs are on for the same time interval. the energy consumed daily is?

A.

0.96 kWh

B.

19.2 kWh

C.

9.60 kWh

D.

1.92 kWh

Correct answer is B

Energy consumed = power x time
= (60 W x 10 + 40 W x 5) x 24 h
= (600 W + 200 W ) x 24 h
= 800 W x 24h = 19200 w h
= 19.2 kWh

1,938.

An electric generator has e.m.f. of 240 V and an internal resistance of 1Ω if the current supplied by the generator is 20A when the terminal voltage is 220 V, find the ratio of the power supplied to the power dissipated?

A.

11:1

B.

1:11

C.

12:11

D.

11:12

Correct answer is A

Power supplied = I\(^2\) R = 20\(^2\) X 1 = 400 W
Power dissipated = IV = 20 X 220 = 4400 W
(Power supplied)/Power dissipated = 4400 W / 400 W
= 11 / 1 or 11 : 1

1,939.

A short chain is sometimes attached to the back of a petrol tanker to?

A.

generate more friction

B.

ensure the balancing of the tanker

C.

caution the driver when overspeeding

D.

conduct excess charges to the earth

Correct answer is D

The friction between the tanker and air creates charges which the chain conducts to the ground.

1,940.

Short sightedness can be corrected by what type of lens?

A.

Concave lens

B.

Convex lens

C.

Converging lens

D.

Mirrors

Correct answer is A

Shortsightedness is corrected using a concave (curved inwards) lens which is placed in front of a myopic eye