Question

An electric kettle takes a 4A current at 220V . How much time will it take to boil 1kg of water from temperature 20degrees C? The temperature of boiling water is 100degrees C.

1- 4.2min 2- 6.3 min

3- 8.4 min 4- 12.6 min

Answer 1

Given,
Current, I=4A
Voltage, V=220V
$$\begin{gathered} \mathrm{P}=\mathrm{VI} \\ =220\times 4=880\mathrm{J}/\mathrm{s}\mathrm{or}880\mathrm{W} \\ \mathrm{Now}\mathrm{using}, \\ \mathrm{Q}=\mathrm{mc}∆\mathrm{\theta } \\ \mathrm{where}, \\ \mathrm{m}=1\mathrm{kg} \\ \mathrm{c}=4200\mathrm{J}/\mathrm{kg}/\mathrm{K} \\ ∆\mathrm{\theta }=({100}^0\mathrm{C}-{20}^0\mathrm{C})={80}^0\mathrm{C} \\ \mathrm{So},\mathrm{Q}=1\times 4200\times 80=336000\mathrm{J} \\ \mathrm{Now}, \\ \mathrm{Time}\mathrm{taken}\mathrm{in}\mathrm{boiling}\mathrm{of}\mathrm{water}=336000/880=381.81\mathrm{seconds}\mathrm{or}6.3\min \end{gathered}$$