The electric potential of a positively charged body is positive,and the electric potential of a negatively charged body is negative.

Why are alloys used to make standard resistors?

$(a)$ 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?

The units of resistance are ampere.

$A$ battery is a source of maintaining a constant potential difference across two ends of a conductor.

How much current will an electric bulb of resistance $1100 \ \Omega$ draw from a $220 \ V$ source? If a heater of resistance $100 \ \Omega$ is connected to the same source instead of the bulb,calculate the current drawn by the heater.