JAMB Physics Past Questions & Answers

1,766.

Three 4Ω resistors connected in parallel have a potential difference of 16 V applied across them. What is the total current in the circuit?

14 A

12 A

10 A

8 A

View answer & explanation

Correct answer is B

¹/_R = ¹/₄ + ¹/₄ + ¹/₄ = ³/₄
R = ⁴/₃
I = ^V/_R

=	16
	⁴/₃

=	16 x 3
	_4

= 12 A

1,767.

The diagram above shows a balanced metre bridge, the value of x is

75.0 cm

66.7 cm

33.3 cm

25.0 cm

View answer & explanation

Correct answer is C

¹/_R = ¹/₈ + ¹/₈ = ²/₈
∴ R = 4Ω
^l/_l₁ = ^R/_R₁
(x)/(100-x) = 4/8
4(100-x) = 8x
400-4x = 8x
400 = 8x + 4x = 12x
x = 400/12 = 33.3cm

1,768.

A cell of e.m.f 12V and internal resistance 4Ω is connected to an external resistor of resistance 2Ω. Find the current flow.

5 A

4 A

3 A

2 A

View answer & explanation

Correct answer is D

I = E/(R+r)
= 12/6 = 2A

1,769.

Three capacitors of capacitance 2μF, 4μFand 8μF are connected in parallel and a P.D of 6V is maintained across each capacitor, the total energy stored is?

2.52 x 10^-6J

6.90 x 10^-6J

2.52 x 10^-4J

6.90 x 10^-4J

View answer & explanation

Correct answer is C

C = C1 + C2 + C3
= 2 + 4 + 8 = 14μF
V = 6V
Energy = 1/2CV2
1/2 x 14 x 10-6 x 62
= 2.52 x 10-4 J

1,770.

THe velocity of sound in air at 16oC is 340ms-1. What will it be when the pressure is doubled and its temperature raised to 127ºC?

400 ms^-1

4,000 ms^-1

8,000 ms^-1

160,000 ms^-1

View answer & explanation

Correct answer is A

The velocity of sound in air, V∝√T, where T is absolute temperature
Thus V = K√T or K = V/T
V is independent of pressure and density at a fixed temperature.
∴ V1/√T1 = V2/√T2
T1 = 16 + 273 = 289K, V1 = 340ms-1
T2 = 127 + 273 = 400K, V2 = ?