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.