An electric refrigerator rated $400 \ W$ operates $8 \ h$ per day. What is the cost of the energy to operate it for $30$ days at ₹ $3.00$ per $kWh$?

Mention the condition under which charges can move in a conductor. Name the device which is used to maintain this condition in an electric circuit.

The filament of an electric bulb is made of tungsten. Why?

$(a)$ What is the total resistance of $n$ resistors each of resistance $R$ connected in:
$(i)$ series?
$(ii)$ parallel?
$(b)$ Calculate the resultant resistance of $3$ resistors $3 \ \Omega, 4 \ \Omega$,and $12 \ \Omega$ connected in parallel.

State the factors on which the heat produced in a current-carrying conductor depends. Give one practical application of this effect.

In an electrical circuit,two resistors of $2\,\Omega$ and $4\,\Omega$ respectively are connected in series to a $6\,V$ battery. The heat dissipated by the $4\,\Omega$ resistor in $5\,s$ will be ........ $J$.