The potential difference between the terminals of an electric heater is $60\, V$ when it draws a current of $4\, A$ from the source. What current will the heater draw,if the potential difference is increased to $120\, V$ (in $, A$)?

$A$ current of $1 \ A$ flows in a series circuit containing an electric lamp and a conductor of $5 \ \Omega$ when connected to a $10 \ V$ battery. Calculate the resistance of the electric lamp. Now,if a resistance of $10 \ \Omega$ is connected in parallel with this series combination,what change (if any) in the current flowing through the $5 \ \Omega$ conductor and the potential difference across the lamp will take place? Give reason.

State Joule's law of heating.

What is the equivalent resistance of a circuit when three resistors of $5 \Omega$,$10 \Omega$,and $30 \Omega$ are connected in parallel (in $Omega$)?

Two lamps,one rated $100 \, W$ at $220 \, V$ and the other $60 \, W$ at $220 \, V$,are connected in parallel to a $220 \, V$ supply. Find the current drawn from the supply line.

$A$ hot plate of an electric oven connected to a $220 \ V$ line has two resistors $A$ and $B$ each of $22 \ \Omega$ resistance. These resistors may be used separately,in series,or in parallel. Find the current flowing in all the three cases.