COMMERCIAL UNIT OF ELECTRICAL ENERGY AND POWER

If one bulb gets fused (or blows off), then the circuit breaks and all the bulbs are turned off
In series circuit, the appliances do not get the same voltage (220 V) as that of the power supply line
In series circuit, the appliances do not get the same voltage (220 V) as that of the power supply line

if one electrical appliance stops working due to some defect, then all other appliances keep working normally
each electrical appliance gets the same voltage (220 V) as that of the power supply line.
the overall resistance of the household circuit is reduced due to which the current from the power supply is high.

ELECTRIC POWER

The rate of doing work is called power
Electric power is the electrical work done per unit time
Power = Work done /Time taken
The power of 1 watt is a rate of working of 1 joule per second.
A bigger unit of electric power called kilowatt is used for commercial purposes.
1 kilowatt = 1000 watts or 1 kW = 1000 W
When an electrical appliance consumes electrical energy at the rate of 1 joule per second, its power is said to be 1 watt.
The rate at which electrical work is done or the rate at which electrical energy is consumed, is called electric power

Power = Work done / Time taken

the work done W by current I when it flows for time t under a potential difference V is given by :

W =V × I × t joules

Sample Problem :

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be : (a) 100 W (b) 75 W (c) 50 W (d) 25 W

A refrigerator having a power rating of 450 W operates for 15 hours a day. Calculate the cost of electrical energy to operate it for a month of 30 days. The rate of electrical energy is Rs. 3 per kWh.
An electric heater draws a current of 15 A from a 220 V supply. What is the cost of using the heater for 5 hours everyday for 30 days if the cost of 1 unit (1 kWh) is Rs. 10
What will be the current drawn by an electric bulb of 40 W when it is connected to a source of 220 V ?