Electricity And Magnitism, Resistance

Electricity and Magnetism Level 1

An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater in joules per second.

1800J/s 2000J/s 1600J/s 1850J/s

Ankit Vijay by Ankit Vijay , 22, India

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3 solutions

Ankit Vijay
Jun 2, 2014

Rate of heat produced by a device is given by the expression for power as

P = I 2 R P=I^{ 2 }R

Where,

Resistance of the electric heater, R = 8 Ω R = 8 Ω

Current drawn, I = 15 A I = 15 A

P = ( 15 2 ) × 8 P = 1800 J / s P=({ 15 }^{ 2 })\times 8\\ P=1800J/s

Therefore, heat is produced by the heater at the rate of 1800 J / s 1800 J/s

4 Helpful 0 Interesting 0 Brilliant 0 Confused

What about time?

B Sharan - 6 years, 7 months ago

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The amount of time does not change the answer since power is a function of current and resistance, both of which are independent of time in this case. It is a bit of a red herring

Caleb Townsend - 6 years, 4 months ago
Aditya Paul
May 31, 2015

Heat 🔥 is an energy while answer is in power units so its wrong.

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Padma Vathi
Jun 4, 2014

Rate of heat produced by the device is given by (I^2)R 225 8=1800 (or) P=VI V=IR V=15 8 V=120 P=(120)15 P=1800J/s

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