A moter operating or `120V` draw a current of `5A`. If the heat is developed in the motor at the one of `12` cells. What is in effeciency ?

Answer

`0.86%`

Explanation

Power applied in motor `VI = 120 xx 3W`
power loss in the from of heat `= 12 cal s^(-1)`
`= 12 xx 4.2 ls^(-1) = 504 Js^(-1)`
power delivered by motor `= 360 - 504 = 309.6 Js^(-1)`
Effective eta = (power delivered by motor )/(power supplied to motor)`
`= (309.6)/(360) = 0.86%`