The electrical resistivity of a few materials is given below in ohm-metre. Which of these materials can be used for making the element of a heating device?

$A$. $6.84 \times 10^{-8} \, \Omega m$

$B$. $1.60 \times 10^{-8} \, \Omega m$

$C$. $1.00 \times 10^{-4} \, \Omega m$

$D$. $2.50 \times 10^{12} \, \Omega m$

$E$. $4.40 \times 10^{-5} \, \Omega m$

$F$. $2.30 \times 10^{17} \, \Omega m$

The potential difference across a conductor is doubled,the rate of generation of heat will

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.

Why is heat produced when a current is passed through a conductor?

$(a)$ Why is the series arrangement not used for domestic circuits?
$(b)$ Why is tungsten used almost exclusively for the filament of electric lamps?
$(c)$ Why are the conductors of electric heating devices,such as bread toasters and electric irons,made of an alloy rather than a pure metal?
$(d)$ Why are copper and aluminium wires usually employed for electricity transmission?
$(e)$ Why does the cord of an electric heater not glow while the heating element does?

What is the commercial unit of electric energy?