WAEC Past Questions and Answers - Page 3551

17,751.

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

17,752.

Economic as a field of study is a

A.

Pure science

B.

Political science

C.

Social science

D.

Physical science

Correct answer is C

No explanation has been provided for this answer.

17,753.

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

17,754.

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

17,755.

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\(\mu F\)