Calculate the time in which 4.8 kJ of energy would be expended when an electric

PHYSICS

WAEC 1992

Calculate the time in which 4.8 kJ of energy would be expended when an electric heater of resistance 1.8 x 103Ω is used on a 240 V mains supply. (Neglect heat losses to the surrounding).

A. 150.0s
B. 90.0s
C. 36.0s
D. 20.0s

Correct Answer: A. 150.0s

Explanation

E = V²t/R

t =

ER/V²

4800 x 1.8 x 10³/240 x 240

= 150s

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