Question

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

Answer 1

$\bigstar\huge\underline{\mathtt{Solution:}}$

♣Part - I :

As per the given question ,

• Power = 40 W
• Voltage = 220 V

We need to find the current flowing through the bulb in order to do that use the power formula

➽ P = V x I

➝ I = P / V

➝ I = 40 / 220

➝ I = 0.18 A

Now let's find the resistance of the bulb

➝ P = V × I

Substituting I by V / R ( By using ohm's law )

➽P = V ² / R

➝ R = V ² / P

➝ R = 48400 / 40

➝ R = 1210 Ω

♣Part - II :

As per the given question ,

Power = 25 W

Voltage = 220 V

We need to find the current flowing through the bulb in order to do that use the power formula

➽ P = V x I

➝ I = P / V

➝ I = 25 / 220

➝ I = 0.11 A

Now let's find the resistance of the bulb

➝ P = V × I

Substituting I by V / R ( By using ohm's law )

➽P = V ² / R

➝ R = V ² / P

➝ R = 48400 / 25

➝ R = 1936 Ω

• We can clearly see that by changing the bulb the resistance and the current flowing through the bulb changes

♠ Change in resistance = 1936 -1210 = 726 Ω

♠ Change in current = 0.18 - 0.11 = 0.07 A