Calculate the time in which 4.8 kJ of energy would be expended when an electric heater of resistance 1.8 x 10<sup>3</sup>Ω is used on a 240 V mains supply. (Neglect heat losses to the surrounding).

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).

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
E 2.7s.

waec 1992 physics

The correct answer is A. 150.0s

E = V²t/R

t = ER/V² = 4800 x 1.8 x 10³/240 x 240 = 150s

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