A carbon filament has a resistance of $100 \mathrm{\Omega }$ at $0°\mathrm{C}$. What must be the resistance of a copper filament placed in series with carbon so that the combination has the same resistance at all temperatures? Temperature coefficient of resistance of carbon$=-{0.0007}^{\circ }{\mathrm{C}}^{-1}$ and that of copper is $0.004°{\mathrm{C}}^{-1}$.

Five $4\mathrm{\Omega }$ resistances, a $2\mathrm{V}$ battery and an ammeter are connected as shown in . Find, the ammeter reading.

Calculate the steady-state current through $2\mathrm{\Omega }$ resistor in the circuit shown in Fig. The internal resistance of the battery is negligible and $\mathrm{C}=2\mathrm{\mu F}$

As shown in Fig., a variable rheostat of $2 \mathrm{k\Omega }$ is used to control the potential difference across a $500 \mathrm{\Omega }$ load.

If the resistance $\mathrm{AB}$ is $500 \mathrm{\Omega }$, what is the potential difference across the load?

As shown in Fig., a variable rheostat of $2 \mathrm{k\Omega }$ is used to control the potential difference across a $500 \mathrm{\Omega }$ load.

If the load is removed, what should be the resistance at $\mathrm{BC}$ to get $40 \mathrm{V}$ between $\mathrm{B}$ and $\mathrm{C}$ ?

In the circuit shown in Fig., both the ammeter and the cell have negligible resistance. Three external resistors are identical. When the switch $\mathrm{S}$ is opened, the ammeter reads $0.6 \mathrm{A}$. What will the ammeter read when the switch $\mathrm{S}$ is closed?