Out of the two,a toaster of $1\, kW$ and an electric heater of $2\, kW$,which has a greater resistance?

$(a)$ What is meant by saying that the potential difference between two points is $1$ volt?
$(b)$ Why does the connecting cord of an electrical heater not glow while the heating element does?
$(c)$ Electrical resistivities of some substances at $20^{\circ}C$ are given below:

Silver	$1.60 \times 10^{-8} \, \Omega m$
Copper	$1.62 \times 10^{-8} \, \Omega m$
Tungsten	$5.2 \times 10^{-8} \, \Omega m$
Iron	$10.0 \times 10^{-8} \, \Omega m$
Mercury	$94.0 \times 10^{-8} \, \Omega m$
Nichrome	$100 \times 10^{-6} \, \Omega m$

Answer the following questions in relation to them:
$(i)$ Among silver and copper, which one is a better conductor? Why?
$(ii)$ Which material would you advise to use in electrical heating devices? Why?

How many joules are there in one kilowatt-hour?

Electric current flows through three lamps when arranged in $(a)$ a series and $(b)$ a parallel circuit. If the filament of one lamp breaks,explain what happens to the other two lamps in both cases.

$A$ heater is joined in parallel with a $60\, W$ bulb and connected to the mains. If the $60\, W$ bulb is replaced by a $100\, W$ bulb,will the rate of heat produced by the heater be more,less,or remain the same?

Which of the following is $NOT$ a unit of electrical energy?