Suppose you being an young guy can do a work in 3o minutes.and an old man can do it in 1 hour.It means you have more energy than the old man, and your **rate of doing work is higher than the old man.**

**Power is defined as the work done per unit time.**

Power =WorkDone/TimeTaken

P=W/t

Also in terms of energy consumed is power is equal to **Energy Consumed/TimeTaken**

Units Of Power is Joule/Second = Watt

1 Kilowatt = 1000 watt

1 Megawatt = 10^{6} Watt

1 Horse power or 1 h.p. = 746 watt

**Example**

**A body does 2o joules of work in 10 seconds. what is its power.**

Power = 20/10= 2 Watt

**Example 2**

**What is the power of a pump which takes 20 seconds to lift 2oo kg of water to a tank situated at a height of 20 m.**

**answer**

we know that **power =WorkDone/TimeTaken**

Work done = w = m * g * h

200*10*20=40000J

now P= 40000/20=2000 Watt or 2 Kw.

**Q. An Electric Bulb consumes 7.2 kJ of electrical energy in 2 minutes. What is the power of the Bulb. **

Energy consumed = 7200 J.

Time taken = 120 second

Power = work done / time taken

Power = 7200/120 = 60 watt.

**Q. What is the power of a pump which takes 30 seconds to lift 300 kg of water to a tank situated at a height 40 metre. **

Ans 4 KW,

### Commercial unit of energy

- You have seen electric meter at your house and you must have heard saying this time 60 units of energy consumed . so what is this unit.
- This is actually means 1 Kilowatt Hour and it is the commercial unit of energy
**So,1 Unit means amount of Kilowatt energy consumed in one 1 hour .**- So 1 Kilowatt-hour = 3.6 X 10
^{6}Joule

**A simple Problem**

**A TV set rated 80 watts runs for 10 hours per day for 30 days. If the cost of electricity per unit is 5 rupees, find the bill for that month.**

So here total hours run = 10 *30 = 300

Power consumed= 80*300=24000 watt= 2.4 KWH

Cost of electricity per unit or per KwH = 5 rupees

Cost for 24 Unit = 24*5=120Rupees

**Law of conservation of energy = Energy cannot be created nor be destroyed but can be transformed from one form into another.**