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

Hope it helps..
Sorry for bad handwriting..

Answer 2

The specific heat of water is 4.184 J/g*°C.

mass of given water = 1Kg =1000g.

temperature to be raised =(100oC - 20oC)=80oC.

Heat energy required for this process =m*c*t.

so heat required is =1000*4.184*80 J=334720 J =334.72 KJoules.

electric kettle is operating at 220V.

it is drawing current of 4A.

so its power is = P=V*I

P=220*4=880 Watts.

1 Watt = 1 Joule/sec.

so to provide 334.72 KJ of energy to water it will take

Energy = Power/Time

880 =334720/t

t= 380.36 sec

=6.3 mins