Two conductors,one having resistance $R$ and another $2R$ are connected in turn across a $dc$ source. If the rate of heat produced in the two conductors is $Q_{1}$ and $Q_{2}$ respectively,what is the value of $Q_{1} / Q_{2}$?

$(a)$ Define potential difference between two points in a conductor.
$(b)$ Name the instrument used to measure the potential difference in a circuit. How is it connected?
$(c)$ $A$ current of $2 \, A$ passes through a circuit for $1$ minute. If the potential difference between the terminals of the circuit is $3 \, V$, what is the work done in transferring the charges?

The resistance of a conducting wire is $10\, \Omega$. If a battery of $1.5\, V$ is connected to it,then how much electric current will flow through it (in $, mA$)?

Does an ammeter have a low or a high resistance?

The $I-V$ graphs of two resistors,and their series combination,are shown below. Which one of these graphs represents the series combination of the other two? Give reasons for your answer.

Draw a circuit diagram of an electric circuit containing a cell,a key,an ammeter,a resistor of $2\,\Omega$ in series with a combination of two resistors ($4\,\Omega$ each) in parallel and a voltmeter across the parallel combination. Will the potential difference across the $2\,\Omega$ resistor be the same as that across the parallel combination of $4\,\Omega$ resistors? Give reason.