Find the resistance of the filament of a $100 \mathrm{W}-220 \mathrm{V}$ bulb when glowing. The length and radius of the filament are $0.1 \mathrm{m}$ and $2.5 \times {10}^{-5}$$\mathrm{m}$. Find the specific resistance of the material of the filament.

A lamp marked $15 \mathrm{V}-20 \mathrm{W}$ is connected to a $\mathrm{DC}$ source of $25 \mathrm{V}$ and a resistance $\mathrm{R}$ in series for full illumination Find the current in the circuit.  

In a house having a $220 \mathrm{V}$ line and the following three appliances are operating : $\left(\mathrm{i}\right)$ a $60$ $\mathrm{W}$ bulb $\left(\mathrm{ii}\right)$a $1000 \text{W}$ heater and $\left(\mathrm{iii}\right)$ a $40 \mathrm{W}$radio. Calculate the current drawn by the heater.