# Electric immersion water heater time

1. Mar 7, 2016

### rgold

1. The problem statement, all variables and given/known data
The mechanical equivalent of heat is 1cal=4.18J. The specific heat of water is 1cal/g*K and its mass is 1g/cm^3. an electric immersion water heater rated at 400 W should heat a liter of water from 10C to 30C in about how much time

2. Relevant equations
R=v/i
power=v*i

3. The attempt at a solution
I know the answer is 3.5 minutes but i do not know how to get there. Im pretty lost.

2. Mar 7, 2016

### SteamKing

Staff Emeritus
Work out the units. What is a watt? How many grams of water are in 1 liter?

BTW, the formulas in Section 2 won't help you with this problem, since you don't know voltage, current, or resistance.

3. Mar 7, 2016

### rgold

im still confused i know that a watt is joules per second and that 1000 grams of water in a liter but how do i connect everything?

Last edited: Mar 7, 2016
4. Mar 7, 2016

### drvrm

you should calculate amount of heat required to raise the water from t1 to t2 given -then calculate the time taken by the heater to provide that heat-
heat req.= related to( massxsp. heatx temp diff ) by calorimetric equation

5. Mar 7, 2016

### SteamKing

Staff Emeritus
You need to go back and study the SI system some more. 1 liter contains way more than 100 grams of water.