Question

An electrical heater has resistance of 1252 and is operated from 220 volts power line. If no heat escapes from it how much time is required to raise the temperature of 40 kg of water from 10C to 80C?

• A. 1456 seconds
• B. 1828 seconds
• C. 2708 seconds
• D. 3250 seconds

Answer 1

The correct option is C 2708 seconds

Heat required$=(40\times {10}^3)\times 1\times (80-15)$$=26\times {10}^6$cal
Now, $H=\frac{V^{2}t}{R\times 4.2}$cal

or, $t=\frac{HR\times 4.2}{V^2}$

$\therefore t=\frac{26\times {10}^5\times 12\times 4.2}{220\times 220}=2708$ seconds.