Four bulbs $B_1$, $B_2$, $B_3$ and $B_4$ of $100 \mathrm{W}$ each are connected to $220 \mathrm{V}$ main as shown in the figure. The reading in an ideal ammeter will be

Two cells of emf $2E$ and $E$ with internal resistance $r_1$and $r_2$ respectively are connected in series to an external resistor $R$ (see figure). The value of $R,$ at which the potential difference across the terminals of the first cell becomes zero is

You are provided with $48$ cells, each of emf $2$ volts and internal resistance $4$ ohms. What maximum current can flow in the circuit having an external resistance of $12 \mathrm{\Omega }$?

Two ideal batteries of emf $V_1$ and $V_2$ and three resistances $R_1, R_2$ and $R_3$ are connected as shown in the figure. The current in resistance $R_2$ would be non-zero, if

A solid conductor has a cross-section area $1 {\mathrm{cm}}^2$ and $2 {\mathrm{cm}}^2$, as shown in the figure. A current of $20 \mathrm{A}$ enters at $A$. Then

A potentiometer wire $PQ$ of $1 \mathrm{m}$ length is connected to a standard cell $E_1$. Another cell $E_2$ of emf $1.02 \mathrm{V}$ is connected with a resistance $r$ and switch $S$ (as shown in figure). With switch $S$ open, the null position is obtained at a distance of $49 \mathrm{cm}$ from $\mathrm{Q}$. The potential gradient in the potentiometer wire is :