WAEC Physics Past Questions & Answers - Page 195

971.

An electric bulb is rated 60W, 220V. Calculate the resistance of its filament when it is operating normally

A.

296.7\(\Omega\)

B.

400.0\(\Omega\)

C.

512.2\(\Omega\)

D.

806.7\(\Omega\)

Correct answer is D

P = \(\frac{v^2}{P} = \frac{220^2}{100} = 806.7\Omega\)

972.

Three identical lamps each power 100W are connected in parallel across a potential difference of 250V. Calculate the current in the circuit

A.

7.5A

B.

2.5A

C.

1.2A

D.

0.8A

Correct answer is C

P = IV

I = \(\frac{P}{V} = \frac{3 \times 100}{250} = 1.2A\)

973.

What is the total energy stored by the capacitors?

A.

2.0 x 10-4J

B.

1.0 x 10-4J

C.

9.0 x 10-2J

D.

1.0 x 10-2J

Correct answer is D

Energy = \(\frac{1}{2}CV^2 = \frac{1}{2} \times 2 \times 10^{-6} \times 100^2\)

= 1.0 x 10-2J

974.

What is the effective capacitance in the circuit?

A.

2\(\mu F\)

B.

6\(\mu F\)

C.

18\(\mu F\)

D.

216\(\mu F\)

Correct answer is A

\(\frac{1}{c} = \frac{1}{6} + \frac{1}{6} + \frac{1}{6}\)

= \(\frac{1 + 1 + 1}{6} = \frac{3}{6} = \frac{1}{2}\)

= 2\(\mu F\)

975.

As the plates of a charged variable capacitor are moved closer together, the potential difference between them

A.

increased

B.

decrease

C.

remains the same

D.

is doubled

Correct answer is B

No explanation has been provided for this answer.