Question

it takes 15 minutes to heat 2kg of water at 30 degrees celsius to 100 degrees celsius using an electric kettle of resistance 10 ohm. how much current is taken by the kettle? what is the amount of power consumed by the kettle? if 1kwh costs 60p how much will you pay?

Answer 1

$$\begin{gathered} Here,t=15min=900s \\ Riseintemp={\theta }_2-{\theta }_1=100-30={70}^{0}C \\ m=2kg=2000gm \\ where,c=1cal{g}^{-1}{}^0{C}^{-1} \\ Energyspentinboilingthewater=mc\left({\theta }_2-{\theta }_1\right) \\ =2000X1X70cal \\ =2000X70X4.2J \\ =\frac{2000X70X4.2}{3.6X{10}^6}kWh=0.16kWh \\ Costofboilingwater=0.16X60=9.6paise \\ Energyspentinheatingcoil=Pt=PX900s \\ 588000j=900P \\ P=653.33Watts \\ H=I^{2}Rt=588000j \\ {I}^2=\frac{588000}{10X900}=65.33A^2 \\ I=8.08A \end{gathered}$$