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Q.
A heater of $220\,V$ heats a volume of water in $5$ minutes time. A heater of $110\,V$ heats the same volume of water. Find time of heating.
Current Electricity
Solution:
Heat produced in the first case = $\frac{220^2}{R} \times 5 \times 60$ ...$(i)$
Heat produced in the second case = $\frac{110^2}{R} \times t \, or \, t = \frac{220 \times 220 \times 5 \times 60}{110 \times 110}$
= $20 \times 60s$ = 1200 s