Draw a schematic diagram of an electric circuit consisting of a battery of two cells each of $1.5\, V$,$5\, \Omega$,$10\, \Omega$ and $15\, \Omega$ resistors and a plug key,all connected in series.

Two bulbs $A$ and $B$ are rated as $90 \, W - 120 \, V$ and $60 \, W - 120 \, V$ respectively. They are connected in parallel across a $120 \, V$ source. Find the current in each bulb. Which bulb will consume more energy?

Nichrome is used to make the element of an electric heater. Why?

$(a)$ Resistivity of iron is $10 \times 10^{-8} \; \Omega m$ and of mercury is $94 \times 10^{-8} \; \Omega m$. Which among iron and mercury is a better conductor? Give reason.
$(b)$ Resistivity of a material $A$ is in the range of $10^{10}-10^{14} \; \Omega m$ while that of $B$ is in the range of $10^{-6}-10^{-8} \; \Omega m$. Which of the two will behave as an insulator and why?

The $V-I$ graphs for two wires $A$ and $B$ are shown in the figure. If we connect both the wires one by one to the same battery, which of the two will produce more heat per unit time? Give justification for your answer.

Draw a circuit diagram of an electric circuit containing a cell,a key,an ammeter,a resistor of $2\,\Omega$ in series with a combination of two resistors ($4\,\Omega$ each) in parallel and a voltmeter across the parallel combination. Will the potential difference across the $2\,\Omega$ resistor be the same as that across the parallel combination of $4\,\Omega$ resistors? Give reason.