Page 43 - Basic Electrical Engineering

Electrical energy = Applied voltage, V × total flow of charge, Q

If electrical power is expressed is kW and time in hour, then

Electrical energy = kWh (1.19)

We will now convert kWh into Calories

3
1 kWh = 10 × 60 × 60 Watt second or Joules
5
= 36 × 10 Joules

Since 1 Calorie = 4.2 Joules

Thermal energy

In SI unit* thermal energy is expressed in calories. One calorie indicates the
amount of heat required to raise the temperature of 1 gm of water by 1°C.

This heat is also called the specific heat. If m is the mass of the liquid, S is
the specific heat, and t is the temperature rise required, then the amount of

heat required, H is expressed as

H = mst calories

= 4.2 × mst Joules (since 1 cal = 4.2J) (1.21)
1 calorie = 4.2 Joules, has been established experimentally