Electric Power and Electrical Energy, and Numerical (X CBSE Physics)

Electric Power: it is defined as the rate of change electrical energy dissipated or consumed in an electrical circuit.

SI unit of electric power is “Watt” (W).

1 Watt is defined as the power consumed by a device, when 1A of current passes through it at the potential difference of 1V.

P = VI

1 Watt = 1 Volt × 1 Ampere

Electrical Energy:

 

SI unit of electric power is watt (W).

1W = 1 volt x 1 ampere = 1V x 1A

1 kilo watt or 1kW = 1000 W

Consumption of electricity (electric energy) is generally measured in kilo watt.

Unit of electric energy is kilo watt hour (kWh)

1 kWh = 1000 watt X 1 hour = 1000 W x 3600 s

Or, 1kWh = 3.6 x 10⁶ watt second = 3.6 x 10⁶ J

 

Example 1: If the potential difference is 220 V and the power of bulb is 110W, what is the electric current flowing in the circuit?

Solution: Given, Potential difference, V = 220 V, Power of bulb , P = 110 W

Electric current (I) =?

We know that P = VI

Or, 110 W = 220 V x I

Or, I = 110 W ÷ 220 V = 0.5 A

 

Example 2: If the power of an electric heater is 1000 W and electricity of 240 V is flowing through it, find the electric current in the electric heater.

Solution: Given, Power (P) = 1000 W, Potential difference (V) = 240 V, Electric current (I) =?

We know that P = VI

Or, 1000 W = 240 V x I

Or, I = 1000 W ÷ 240 V = 4.16 A

 

Example 3: What is the electric current through an electric geyser of 500 W, if the potential difference across the electric circuit is 250 V?

Solution: Given, P = 500 W, V= 250 V, therefore, Electric current (I) =?

We know that P = VI

Or, 500 W = 250 V x I

Or, I = 500 W ÷ 250 V = 2 A

 

Example 4: If the electric current is 10 A and potential different between two terminals is 240 V, find the power of the electric appliance.

Solution: Given, Electric current (I) = 10 A, Potential difference (V) = 240 V, Power (P) =?

Since, P = V x I

Therefore, P = 240 V x 10 A = 2400 W

Example 5: Find the power of electric iron, if electric current through the circuit is 5 A and potential difference is 220 V.

Solution: Given, Electric current (I) = 5 A, Potential difference (V) = 220 V, Power(P) =?

We know that, P = V x I

Or, P = 220 V x 5 A = 1100 W