Question

what is the shortest time for which 2.5kw kettle containing 1.5kg of boiling water can be left without boiling dry​

Answer 1

22.6 minutes

Step-by-step explanation:

The energy that must be supplied to the water, in order to completely boil it, is given by:

`Q= m \lambda`

where

m = 1.5 kg is the mass of the water at boiling temperature

`\lambda=2.26\cdot 10^6 J/kg` is the specific latent heat of vaportization of water

Substituting into the equation, we find

`Q=(1.5)(2.26\cdot 10^6)=3.39\cdot 10^6 J`

The power supplied by the kettle is

`P=2.5 kW = 2500 W`

We also know that power is defined as the ratio between energy supplied and time:

`P=(Q)/(t)`

Therefore, the shortest time the kettle must be left on in order to completely boil the water can be found by re-arranging the previous equation:

`t=(E)/(P)=(3.39\cdot 10^6)/(2500)=1356 s= 22.6 min`