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

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Solution

## Step 1: Given dataThe 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 resistanceOhm's law and formula usedThe potential difference across a conductor is directly proportional to the current flowing through it.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, $R=\frac{V}{I}=\frac{4}{0.4}=10\phantom{\rule{0ex}{0ex}}orR=10ohms.$Therefore, the resistance of the bulb when it is glowing is $10ohms.$

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