Question

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

Answer 1

Energy needed for raising the temperature of 1kg water from 20C to 100C is given by E=mcθ where m is the mass of the object in kgs, c is the specific heat capacity ( 4181 in this case) and θ is the temperature change.

So E= 1 * 4181 * (100-20)

       = 4181 * 80

       =  334480 J

Now E = I²Rt

        ( Where R=V/I)

      so, E =$4 * 4 * (220/4) * x$

      x = 334480/880

      therefore time taken ≈ 380.09 seconds

Note: This works only in ideal situations.