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WAEC Physics Past Questions & Answers - Page 157

781.

Which of the following statements explains lost volt in an electric circuit? The

total p.d from a source to maintain a flow of current through the circuit as well as the source

p.d to drive current through the circuit component except the source

p.d across all external components connected to the source of electricity

p.d across the internal resistance of the cell

View answer & explanation

Correct answer is D

The lostvolt is the potential drop in a cell due to internal resistance.

782.

An electric lamp is rated 240V, 40W. What is the cost of running the lamp for 72 hours if the electricity authority charges N2.50 per kWh?

N7.20

N18.00

180.00

N720.00

View answer & explanation

Correct answer is A

Cost = $\frac{Pt}{1000}$ x cost per kWh

= $\frac{40 \times 72}{1000} \times 2.50 = N7.20$

783.

A chemical cell of internal resistance 1 $\Omega$ supplies electric current to an external resistor of resistance 3 $\Omega$ . Calculate the efficiency of the cell

75%

50%

33%

25%

View answer & explanation

Correct answer is A

R = $r_1 + R = 1 + 3 = 4\Omega$

$\frac{3}{4} \times \frac{100}{1} = 75$ %

784.

A parallel plate capacitor of capacitance 600 $\mu F$ has a potential difference of 200V between its plates. Calculate the charge on either plate of the capacitor

1.2C

3.3C

3330.0C

12.0000.0C

View answer & explanation

Correct answer is A

Q = CV

= 600 x 10^-6 x 200 = 1.2C

785.

Two capacitors of capacitance 0.4 $\mu F$ and 0.5 $\mu F$ are connected in parallel and charged to a p.d. of 50V, Determine the total charge acquired

45 $\mu C$

25 $\mu C$

20 $\mu C$

10 $\mu C$

View answer & explanation

Correct answer is A

C = $C_1 + C_2$ = 0.4 + 0.5 = 0.9 $\mu F$

Q = Cv = 0.9 x 50 = 45 $\mu C$

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