Electricity is a forth basic need for living being. We use electric current in domestic and industrial appliances regularly. Why electricity has much importance in today’s life? The answer is that the electrical energy is controlled type of energy.
Electrical power:
As we already discussed about power in class 9th. The rate of change of energy with respect to time is called power.In the concept of power, you focussed on speed of doing work. So it is also defined as ratio of work done to the time. In current electricity it is related to the consumption of electrical energy is called electric power.
Definition: product of current with voltage is called power.
In electrical circuit, battery provides potential difference to flow the electron in the circuit and we know that rate change of flow of electron is called current. So the concept of electrical power is associated with flow of charges and potential difference applied across resistor in a circuit.
Mathematically it is expressed as
P = V × I
Where,
P – electrical power
V – Voltage
I – Current.
Also we can calculate power by using
P = v × I ———-1
But v = I x R
Put in equation 1
P = I² × R———-2
As I = V/R
Put this in equation 1
P = v²/ R ——3
We can use equation 1, 2 and 3 for calculating power.
It has dimensions same as power [M L²T⁻³].
SI unit of power is watt.
There is another unit of power that is horse power(hp). We use this unit mainly in industries. You have 1 hp, 2 hp etc motors in your home.
1 hp = 746 Watt.
When we buy electrical appliances on the basis of power consumption for examples 60 watt bulb, 1500 watt heater etc.
Question and Answer:
Q) If a bulb of power 100 watt is used for 10 hours then calculate energy consumption by the bulb.
Solution:
Given,
Power = 100 watt,
Time = 10 hours = 10× 60 × 60 seconds
Time =36000 second
Power = Energy/ Time
Energy= power × time
= 100 × 36000
=3·6 x 10⁶Joule.
The 100 watt bulb is used for 10 hours then it consumes 3·6 x 10⁶J.
NOTE- conversion of Watt hour to Joule is important and it is , 1 watt hour = 3.6 × 10³
Q) If 220 V voltage applied across the bulb and it drawn 2 A current through it then calculate power consumed by that bulb.
Solution:
Given V = 220 V,. I =. 2 A
We know,
P = V × I
= 220× 2
P = 440 W.
Q) Complete the following table:
Resistance (ohm) |
Current (A) | Voltage (V) | Power (W) |
2 | 5 | ——– |
——– |
——- |
——- | 10 | 20 |
—– | 2 | ——- |
70 |