Heat Generated
Electrical Energy
• Electrical energy is the energy delivered over a
period of time
• Energy (in joules) generated =P(Watts) x t(sec)
• Energy (in kW-h) generated =P(kW) x t(hr)
Sample Problem
1. An electric motor takes 5 A from a 110 V
line. Determine the power input and the
energy in J and kW – h, supplied to the
motor in 2 h.
1. An electric iron of resistance 20 ohms
takes a current of 5 A. Calculate the heat
in Joules developed in 30 seconds.
2. An electric heater of resistance 8 ohms
draws 15 A from the service mains. At
what rate is heat developed in watts?
What is the cost of operating the heater
for a period of 4 h at P4.90/ kW – h
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