The resistance of an ideal voltmeter is

The current passing through the ideal ammeter in the circuit given below is (in $\text{ A}$)

In the given circuit,the internal resistance of the $18\,V$ cell is negligible. If $R_1 = 400\,\Omega$,$R_3 = 100\,\Omega$,and $R_4 = 500\,\Omega$,and the reading of an ideal voltmeter across $R_4$ is $5\,V$,then the value of $R_2$ will be ........... $\Omega$.

Calculate the voltage across $AB$ terminals in the given circuit.

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?