# Efficiency of Electrical Appliance

### Efficiency of Electrical Appliance

1. The efficiency of an electrical appliance is given by the following equation
2. Normally, the efficiency of an electrical appliance is less than 100% due to the energy lost as heat and the work done against friction in a machine.

Example 1
A lamp is marked “240V, 50W”. If it produces a light output of 40W, what is the efficiency of the lamp?

$Efficientcy= P output P input ×100% Efficientcy= 40 50 ×100%=80%$

Example 2
An electric motor raises a mass of 2kg to a height of 5m in 10s. If the input current from a source of 12V is 2A, find the efficiency of the electric motor.

Input power,
$P=IV P=(2)(12) P=24W$
Output power
$P= W t P= mgh t P= (2)(10)(5) 10 =10W$
$Efficientcy= P output P input ×100% Efficientcy= 10 24 ×100%=41.7%$