Question

An electric heater rated ‘2.2 kW, 220 V’ is operated for 2 hours. Calculate:

i. Safe current

ii. Cost of electricity @ Rs. 5.20/ unit​

Answer 1

Answer:

Power is energy consumed per unit time.

Here, energy consumed=P=2kW=2000W and time=t=10hr=36000s

P=

t

E

⟹E=Pt=2kW×10h=20kWh=20units

Since 1unit=1kWh

Cost=20×350=Rs7000

Answer 2

Given,

P = 2.2 kW = 2200 W

220 V is operated in 2 hours

To find,

i. Safe current

ii. Cost of electricity @ Rs. 5.20/ unit

Solution,

i) We will calculate the safe current with the help of the formula which is given below:

I = P/V

Putting the values in the formula:

We will get, I = 2200W/220V

I = 10 A

ii) For calculating the cost of electricity will first calculate the electrical energy consumed

Its formula is given below:

The electrical energy consumed = power × time

Putting the values in the formula:

The electrical energy consumed = 2.2 kW × 2 h

The electrical energy consumed = 4.4 kWh

The cost of electricity = 4.4 kWh × Rs. 5.2

The cost of electricity= Rs. 22.88

Hence, the safe current is 10 A and the cost of electricity is Rs. 22.88