Question

An electric heater of resistance 8 ohm draws 15 A from the service mains 2 hours. Calculate the rate which heat is developed in heater​

Answer 1

Given,

Resistance in electric heater , R = 8 ohm

Current , I = 15 A

Time taken , t = 2 hrs = 3600*2 sec = 7200 sec

The rate at which work is done by a source of emf in maintaining an electric current through a circuit is called the electric power of the circuit.

Power = current * voltage

Thus ,

The rate at which heat is developed  in 2 hr is known as its power ,

$P= I^{2} R$

on putting the values,

= 15*15 * 8

= 1800 Watt.

Thus the rate at which heat is developed in heater is 1800 Watt.

Answer 2

Answer: 1800 J/s

Explanation:

Given,

Resistance(R) = 8 Ω

Current (i) = 15 A

Time (t) = 2 hr. = 2×60×60 = 7200 second

P = Vit × cosФ

Where Ф is phase difference between V and i.

Since, this heater is treated as pure ohm's circuit. Therefore Ф=0

cosФ = cos0° = 1  

So,

P = Vi 

Again using ohm's law,

Putting V = iR

P = I²R

P = 15×15×8

P = 1800 J/s