Solution:
Mass of water = 450 g
Rise in temp = 100 – 20 = 800C
Heat produced = 450 × 1 × 80 = 36000 cal
E = 250 volts
= 4 A
t = ?
\(\begin{array}{l}H=frac{Etimes Itimes t}{4.2}\end{array} \)
\(\begin{array}{l}36000=frac{250times 4times t}{4.2}\end{array} \)
\(\begin{array}{l}t=frac{36000times 4.2}{250times 4}=151.2s\end{array} \)
\(\begin{array}{l}t=frac{151.2}{3600}hour\end{array} \)
Energy consumed
\(\begin{array}{l}=frac{Etimes Itimes t}{1000}kWh\end{array} \)
\(\begin{array}{l}=frac{250times 4times 151.2}{1000times 3600}=0.042kWh\end{array} \)
Rate = 20 P a unit
Cost = 0.042 × 20 = 0.84 P
