JAMB Physics Past Questions & Answers - Page 449

2,241.

when a piece of rectangular glass block is inserted between two parallel capacitor,at constant plate area and distance of separation, the capacitance of the capacitor will

A.

increase

B.

decrease

C.

decrease then increase

D.

remain constant

Correct answer is A

No explanation has been provided for this answer.

2,242.

In a Daniel cell, the depolarizer, positive and negative electrodes are respectively

A.

copper sulphate, copper and zinc

B.

manganese dioxide, carbon and zinc

C.

sulphuric acid, lead oxide and lead

D.

potassium hydroxide, nickel and iron.

Correct answer is A

In the Daniel cell,
i. Depolarize = CuSO4 solution
ii. Positive electrode = Copper container
iii Negative electrode = zinc rod/plate

2,243.

The cost of running five 60 W lamps and four 100 W lamps for 20 hours if electrical energy cost #10.00 per kwh is

A.

280.00

B.

160.00

C.

120.00

D.

140.00

Correct answer is D

Total power in watt = 60*5 + 4*100
= 300 + 400
= 700w
Total power in kilo watt = 700/1000
= 0.7 killo w
Unit of electricity in killo watt-hour
= 0.7 * 20hrs
= 14 okwh
i.e If I kwh costs # 10.00
14kwh = 10.00 * 14 = #140

2,244.

A working electric motor takes a current of 1.5 A when the p.d across it is 250V. If its efficiency is 80%, the power output is

A.

300.0W

B.

469.0W

C.

133.0W

D.

4.8W

Correct answer is A

Efficiency = power output/power Input
=> 80/100 = power output/1.5 * 250
i.e power output = 1.5*250 *80/100 =300w

2,245.

A student is at a height 4m above the ground during a thunderstorm. Give that the potential difference between the thundercloud and the ground is 107v, the electric field created by the storm is

A.

2.0 * 106 NC -1

B.

2. 5 * 106 NC -1

C.

1.0 * 107 NC -1

D.

4.0 * 107 NC -1

Correct answer is B

v = E*d, => E = v/d
i.e E 107/4 = 2.5 * 106 NC-1