# Quantum energy vs heat

1. Oct 9, 2012

### moonman239

If I microwave an insulated cup of water or expose it to sunlight, how do I determine the amount of heat energy? Do I use the equation E=hv, where h = Planck's constant and v = the frequency of the microwaves?

2. Oct 10, 2012

### Enthalpy

This would work if you knew how many photons are absorbed. Though formally feasible, such a method is quite indirect. Normal people would use the power, or the power density, of the light or microwave source to compute the power absorbed and converted into heat.

3. Oct 16, 2012

### moonman239

Ok.

I leave a cup of water out in the sun. Currently, the temperature of the water is 23 degrees Celsius. Assuming no heat loss, calculate the time the water will take to boil if the boiling point is 100 degrees.

4. Oct 17, 2012

### Staff: Mentor

Do you know the surface area (as seen from the sun)?
Do you know the heat capacity of your cup of water?

On a bright day, sunlight has a power of about 1 kW/m^2. Some parts will be reflected, but I think you can neglect that.