Question

A blub of 40W is connected across a source of 220V . Find the resistance of the blub. ​

Answer 1

Given:

Power (P) = 40W

Voltage (V) = 220 V

To find:

Resistance of the bulb.

Solution:

Ohm's Law: It states that current through a conductor between two points is directly proportional to the voltage across two points.

Symbolically it can be represented as,

V ∝ I

On removing the sign of proportionality, we add a constant.

⇒ V = IR

⇒ I = $\frac{V}{R}$

Now, we know that,

P = VI

and, P = V ($\frac{V}{R}$)

⇒ P = $\frac{V^{2} }{R}$

⇒ R = $\frac{V^{2} }{P}$

On substituting the given values,

⇒ R = $\frac{220^{2} }{40}$

⇒ R = $\frac{48400}{40}$

⇒ R = 1210 ohm

Thus, resistance of the bulb is 1210 ohm.