In the given circuit,find $V_a - V_b$.

$A$ current of $2 \, A$ flows in an electric circuit as shown in the figure. The potential difference $(V_R - V_S)$, in volts ($V_R$ and $V_S$ are potentials at $R$ and $S$ respectively) is:

In the adjacent circuit,a voltmeter of internal resistance $R$,when connected across $B$ and $C$,reads $\frac{100}{3} \ V$. Neglecting the internal resistance of the battery,the value of $R$ is ................. $k \Omega$.

Twelve wires each having resistance $2 \Omega$ are joined to form a cube. $A$ battery of $6 \text{ V}$ emf is connected across points $a$ and $c$. The voltage difference between $e$ and $f$ is . . . . . . $\text{V}$.

$A$ student connects a voltmeter,ammeter,and resistance according to the circuit given. If the voltmeter reading is $20\, V$ and the ammeter reading is $4\, A$,then the resistance $R$ will be:

$A$ $d.c.$ main supply of $e.m.f. \, 220 \, V$ is connected across a storage battery of $e.m.f. \, 200 \, V$ through a resistance of $1 \, \Omega$. The battery terminals are connected to an external resistance $'R'$. The minimum value of $'R'$ so that a current passes through the battery to charge it is ............... $\Omega$.