Past Year - 5 Mark Questions

Class 10
Chapter 12 Class 10 - Electricity

A bulb is rated 40W, 220V. Find the current drawn by it, when it is connected to a 220V supply. Also find its resistance. If the given bulb is replaced by a bulb of rating 25W, 220V,will be there be any change in the value of current and resistance? Justify your answer and determine the change.

Answer:

Case 1:

Given,

• Power, P = 40 W
• Potential difference, V = 220 V

Let I be the current through the bulb and R be the resistance.

We know that,

P = V * I

I = P / V

= 40 / 220

= 0.18 A

We know that resistance is given as

R = V 2 / P

= (220) 2 / 40

=  1210 ohm.

Therefore,

• The current drawn by the bulb = 0.18 A
• The resistance of the bulb = 1210 ohm

Case 2:

Given,

• Power, P = 25 W
• Potential difference, V = 220 V

Let I be the current through the bulb and R be the resistance.

We know that,

P = V * I

I = P / V

= 25 / 220

= 0.113 A

We know that resistance is given as

R = V 2 / P

= (220) 2 / 25

=  1936 ohm.

Therefore,

• The current drawn by the bulb = 0.113 A
• The resistance of the bulb = 1936 ohm

Thus, there is a change in the value of current and resistance in the two cases.

The current in case 1 is more since its resistance is lesser than the resistance of case 2.

Made by

Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo