WAEC Past Questions and Answers - Page 3230

16,146.

Two identical charges situated 20cm apart in vacuum repel each other with a force of 1.0N.Calculate the value of each other with a force of 1.0N. Calculate the value of each charge. [(14 \(\pi \varepsilon_o)^{-1}\) = 9 x 109Nm2C-2]

A.

21\(\mu C\)

B.

3.6\(\mu C\)

C.

4.0\(\mu C\)

D.

4.4\(\mu C\)

Correct answer is A

F = \(\frac{Q^2}{4 \pi \varepsilon_o r^2}\)

I = 9 x 109 x \(\frac{Q^2}{0.2^2}\)

Q = \(\sqrt{\frac{0.04}{9 \times 10^9}}\)

= 2.11 x 10-6

16,147.

A 15 \(\mu F\) capacitor is connected to a 240V, 50Hz ac. source. Calculate the reactance of the capacitance [\(\pi = 3.142\)]

A.

16\(\Omega\)

B.

68\(\Omega\)

C.

106\(\Omega\)

D.

212\(\Omega\)

Correct answer is D

\(X_c = \frac{1}{2 \pi fc}\)

= 2 x 3.142 x 50 x 15 x 10-6

= 212.179\(\Omega\)

16,148.

An electric motor converts

A.

electrical energy to mechanical energy

B.

mechanical energy to electrical energy

C.

mechanical energy to chemical energy

D.

electrical energy to thermal energy

Correct answer is A

No explanation has been provided for this answer.

16,149.

Which of the following conditions occur at resonance in a series RLC circuit? i. Impedance equals resistance ii. Current is maximum iii. Reactance is maximum iv. Current and voltage are 90° out of phase

A.

i and ii only

B.

i and iii only

C.

i, ii and iii only

D.

i, ii, iii and iv

Correct answer is A

conditions for the occurrence of resonance in a series RLC circuit are i) impedance is at minimum ie when inductive and capacitive reactances are equal ii) when current is maximum

16,150.

The energy stored in a simple cell is

A.

electrical

B.

nuclear

C.

thermal

D.

chemical

Correct answer is D

No explanation has been provided for this answer.