An electric lamp is connected with a battery of emf 10 V and it is found that 0.01A current is flowing through it. But if the lamp is connected with 220 volt mains, a constant current of 0.05A flows through it. Explain the apparent anomaly with Ohm's law.

Explanation

For an emf of 10V,current =0.01 A,
resistance `=10/0.01=1000 Omega`
`therefore` For an emf of 220 V, expected current `=0.01 times 220/10 =0.22 A`(fro, Ohm's law)
But the observed current =0.05A, At this means that the resistance `=220/0.05=4400 Omega`
So the resistance of the lamp increases from `1000 Omega` and `4400 Omega` this is expected, because the higher voltage produces greater amount of heat, and so a higher temperature. Then resistance of the metallic coil increases the to this rise in temperature.