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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 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,

R=VI=40.4=10orR=10ohms.

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


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