An electric geyser consumes 2.2units of electrical energy per hour of its use. It is designed to work on 220v. What is the resistance of this device? Find the cost of energy consumed if each unit costs Rs 6.00.

Explanation:

The resistance of this device is determined by using the formuia from Ohms Law:

V = IR

where; V = voltage

I = current

R = resistance

From the above equation:

R = V/ I (1)

And

I = P/V    --- (2)

If 1 unit = 1 KWH = 3.6 × 10⁶ J

Then;

2.2 units = (3.6 × 10⁶ × 2.2)

= 7.92 × 10⁶ J

So, Energy = 7.92 × 10⁶ J

Also:

Power = energy/time

Power =  7.92 × 10⁶ J / 1 hour

Power = 7.92 × 10⁶ J / 3600 seconds

Power = 2200 Watts

From equation (2)

I = P/V

I = 2200/220

I = 10 A

Recall that:

Resistance R = V/I

Resistance R = 220/10

Resistance R = 22 ohms

SO, if 1 unit costs = Ts 6.00

Then the cost of 2.2 unit = 2.2 ( Rs  6.00)

= Rs 13.20