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**We know that in a battery chemical reaction takes place to produce electrical energy, maximum amount of electrical energy****are used to d useful work but some part of energy is converted to heat energy.**

**You might have observed that when fan runs for a longer time it gets heated.**

**This effect is used heating purposes like heater,iron etc.**

**If all the appliances are resistive then total energy is converted to heat energy.****We can also find how much of heat is produced.****Consider a current I flowing through a resistor of resistance R.**

**Let the potential difference across it be V.**

**Let t be the time during which a charge Q flows across.**

**The work done in moving the charge Q through a potential difference V is VQ.**

**Therefore, the source must supply energy equal to VQ in time t.**

**Hence the power input to the circuit by the source is**

**P=VQ/t=VI**

**Or the energy supplied to the circuit by the source in time t is P × t, that is, VIt****.**

**the amount of heat H produced in time t is****H = VIt****.**

**Applying Ohm’s law we get**

**H = I**^{2}Rt**.**

Visit Here to download NCERT Solutions For Science for Class 10th

*lets do a problem
An electric iron consumes energy at a rate of 840 W when heating is at the maximum rate and 360 W when the heating is at the minimum. The voltage is 220 V. What are the current and the resistance in each case?
*

*solution.
From the previous equation we know that the power input is P = V I Thus the current I = P/V
*

(b) When heating is at the minimum rate, I = 360 W/220 V = 1.64 A; and the resistance of the electric iron is R = V/I = 220 V/1.64 A = 134.15 Ω.

**Now we will study about Electric Power.**

**We know that power is the rate of doing work.**

**So, Electric power is the rate of doing electrical work.**

**It is also called as the rate of consumption of electrical energy.**

**The power P is given by:- P=VI**

**Or, P=I**^{2}R=V^{2}/R

**The SI unit of electric power is Watt(W).**

**It is the power consumed by a device that carries 1 A of current when operated at a potential difference of 1 V.**

**Thus, 1 W = 1 volt × 1 ampere = 1 V A.**

**The unit ‘watt‘ is very small. so****commercially Kilowatt is used. which is equal to 1000watt.**

**Since electrical energy is the product of power and time, the unit of electric energy is, therefore, watt hour (W h).**

**One watt hour is the energy consumed when 1 watt of power is used for 1 hour.****The commercial unit of electric energy is kilowatt hour (kW h), commonly known as ‘unit’.**

1 kW h = 1000 watt × 3600 second = 3.6 × 10^{6}watt second = 3.6 × 10^{6}joule (J)

Visit Here to download NCERT Solutions on Physics for Class 10th

These are Few questions asked in Previous Years In the board exam. Solve these Problems and upload the answer by clicking a photo of those answers.

- What Is Electricity
- Write ohm’s Law
- What is Heating effects of Electric Current
- When I double the length of a wire keeping its area constant Mention the effect on its resistance
- What is Voltage

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