$A$ house is fitted with $5$ tubes each of $40 \, W$. If all the tubes are lighted for $20$ hours and if the cost of electrical unit is ₹ $0.50$,the total cost of electricity consumed is (in ₹)

$(a)$ 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?

Three $2\,\Omega$ resistors,$A$,$B$,and $C$,are connected as shown in the figure. Each of them dissipates energy and can withstand a maximum power of $18\,W$ without melting. Find the maximum current (in $A$) that can flow through the circuit such that none of the resistors melt.

$(a)$ What material is used in making the filament of an electric bulb?
$(b)$ Name the characteristics which make it suitable for this.

Two bulbs are marked $60\, W, 220\, V$ and $100\, W, 220\, V$. These are connected in parallel to a $220\, V$ mains. Which one out of the two will glow brighter?

How can we measure the potential difference across the ends of a conductor?