Question

A small bulb has resistance $2ohms$ when it is cold. It draws $0.4ampere$ current from a source of $4volt$ and then starts glowing. Calculate the resistance when it is glowing

Answer 1

Step 1: Given data

The resistance of the bulb, when it is cold is $2ohms$.

The current through the bulb is $I=0.4A$

The voltage across the bulb is $V=4volt.$

Step 2: Finding the resistance

Ohm's law and formula used

1. The potential difference across a conductor is directly proportional to the current flowing through it.
2. Ohm's law is defined by the form, $V=IR$, where, V is the potential difference, I is the current through the conductor and R is the resistance of the conductor.

So, from Ohm's law $V=IR$. Now,

$$\begin{gathered} R=\frac{V}{I}=\frac{4}{0.4}=10 \\ orR=10ohms. \end{gathered}$$

Therefore, the resistance of the bulb when it is glowing is $10ohms.$