# Question #72bfa

##### 1 Answer

See example below:

#### Explanation:

Supose you want to heat 2 liters of water using an electric heater.

The water has to be heated from

The heater is thermal insulated from the environment.

How much time wil be taken to do the job?

First, we have to calculate the work, in calories:

where:

m = mass in (g)

c = specific heat of water = 1

As the water specific mass=1, 2 liters of water have 2000g

(m=2000g).

The electrical power of the heater is:

The electrical work in Joules is equal to:

where:

W = Electrical Work, in Joules

P = Electrical Power, in Watts

t = time, in seconds

To convert calories in Joules, we use the equation: