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JAMB Physics Past Questions & Answers - Page 313

1,561.

The power dissipated in an a.c. circuit with an r.m.s, current of 5A, r.m.s voltage of 10V and a phase angle of 60^o is

25W

50W

120W

125W

View answer & explanation

Correct answer is A

P = IVcos $\theta$

= 5 x 10 x cos60

= 25W

1,562.

What is the total electrical energy consumed by using an electric cooker rated 1000W for 5 hrs?

5.3 x 10³J

6.5 X 10³J

1.8 X 10⁷J

2.3 X 10⁷J

View answer & explanation

Correct answer is C

Energy = power x time

= 1000 x 5 x 3600

= 1.8 X 10⁷J

1,563.

Two 50 $\mu$ F parallel plate capacitors are connected in series. The combined capacitor is then connected across a 100-V battery. The charge on each plate of the capacitor is

5.00 x 10^-5C

2.50 x 10^-3C

1.25 x 10^-3C

1.00 x 10^-2C

View answer & explanation

Correct answer is D

For series, C = $\frac{50 \times\ 50}{50 + 50}$

C= 25 $\mu$ F

Q = CV

Q = 25 x 100 x 10^-3

Q = 2.5 x 10^-3C

1,564.

In a meter bridge experiment, two resistor 2 $\Omega$ and 3 $\Omega$ occupy the left and right gaps respectively. Find the balance point from the left side of the bridge

20cm

40cm

60cm

80cm

View answer & explanation

Correct answer is B

Let the point be x

$\frac{2}{x}$ = $\frac{3}{100 - x}$

making x subject of formula,

2(100 - x) = 3x

200 - 2x = 3x

200 = 3x + 2x

200 = 5x

divide both side by 5

x = 40cm

1,565.

If 8 x 10 $^{-2}$ J of work is required to move 100 $\mu$ C of charge from a point X to a point Y in an electrical circuit, the potential difference between X and Y is

4.0 x 10² v

4.0 x 10⁴ v

8.0 x 10² v

8.0 x 10^-2 v

View answer & explanation

Correct answer is C

V = $\frac{W}{Q}$

V = $\frac{8 \times\ 10^{-2}}{100 \times\ 10^{-6}}$

V = 8.0 x 10 $^2$ v

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