The potential difference across $A$ and $B$,i.e.,$V_A - V_B$,is ......... $V$.

When a resistor of $11 \Omega$ is connected in series with an electric cell,the current flowing in it is $0.5 \ A$. Instead,when a resistor of $5 \Omega$ is connected to the same electric cell in series,the current increases by $0.4 \ A$. The internal resistance of the cell is (in $\Omega$)

If $X, Y$ and $Z$ in the figure are identical lamps,which of the following changes to the brightness of the lamps occur when switch $S$ is closed?

Three voltmeters,all having different internal resistances,are connected as shown in the figure. When a potential difference is applied across $A$ and $B$,their readings are $V_1, V_2$,and $V_3$. Choose the correct option.

Which of the following acts as a circuit protection device?

$A$ $dc$ source of $emf \, E_1 = 100 \, V$ and internal resistance $r = 0.5 \, \Omega$,a storage battery of $emf \, E_2 = 90 \, V$,and an external resistance $R$ are connected as shown in the figure. For what value of $R$ will no current pass through the battery $E_2$ (in $.5$)? ................ $\Omega$