Given:
\(\mathrm{V}=3 \mathrm{~V}  \)
\(\mathrm{I}=600 \mathrm{~mA}=600 \times 10^{-3} \mathrm{~A},  \quad \text { time }=4 \text { hours }  \)
\(\text { Power }=?, \text { resistance }=?,\quad \text { energy =? }\)
(a) Power = \(\mathrm{V} \times \mathrm{I}\)
\(=3 \times 600 \times 10^{-3}=1.8 \mathrm{~W}\)
(b) Resistance \(=\frac{V}{I}\)                [\(\because\) V = IR]
\(=\frac{3}{600 \times 10^{-3}}=5 \Omega\)
(c) Energy consumed in 4 hours
= \(\mathrm{P} \times \mathrm{t} \)
= 1.8 x 4  = 7.2 Wh

Given:
Energy consumed when heating is maximum at the given rate \((P_{1})=420 \mathrm{~W}\)
Energy consumed when heating is minimum at a given rate \(P_{2}=180 \mathrm{~W}\) 
Applied voltage = 220 V
Current in each case = ?
\(\mathbf{P}=\mathbf{V} \times \mathbf{I}\)
case (i) : \(\mathrm{I}_{1}=\frac{\mathrm{P}_{1}}{\mathrm{~V}}=\frac{420}{220}=1.9 \mathrm{~A}\)
case (ii) : \(\mathrm{I}_{2}=\frac{\mathrm{P}_{2}}{\mathrm{~V}}=\frac{180}{220}=\mathbf{0 . 8 1} \mathbf{A}\)

(i) The earth wire provides a low resistance path to the electric current.
(ii) The earth wire sends the current from the body of the appliance to the Earth, whenever a live wire accidentally touches the body of metallic electric appliance.
(iii) Thus, the earth wire serves as a protective conductor, which saves us from electric shock.

Electric potential : The electric potential at a point is defined as the amount of work done in moving a unit positive charge from infinity to that point against the electric force.
Electric potential difference : The electric potential difference between two points is defined as the amount of work done in moving a unit positive charge from one point to another point against the electric force.