Page 49 - Basic Electrical Engineering

Power, P = 1.74 kW = 1740 Watts.
V = 230 V

Example 1.7 Calculate the current flowing through a 60 W lamp on a 230 V

supply when just switched on at an ambient temperature of 25°C. The
operating temperature of the filament material is 2000°C and its temperature

coefficient of resistance is 0.005 per degree C at 0°C.

Solution:

We know, power,

Here, W = 60 W, V = 230 V

∴

This resistance of the filament is at 2000°C. Let us call it R 2000 = 881.6

Ohms.

At the instant of switching, resistance is at room temperature, i.e., at 25°C.

Let us call it as R .
25

We know R 2000 ; we have to calculate R given α = 0.005 ohm/°C.
0
25

We know,