coffee

[logistic_guy]

Microwave ovens use microwave radiation to heat food. The energy of the microwaves is absorbed by water molecules in food and then transferred to other components of the food. \(\displaystyle \bold{(a)}\) Suppose that the microwave radiation has a wavelength of \(\displaystyle 11.2 \ \text{cm}\). How many photons are required to heat \(\displaystyle 200 \ \text{mL}\) of coffee from \(\displaystyle 23\) to \(\displaystyle 60^{\circ}\text{C}\)? \(\displaystyle \bold{(b)}\) Suppose the microwave’s power is \(\displaystyle 900 \ \text{W} \ (1 \ \text{watt} = 1 \ \text{joule/second})\). How long would you have to heat the coffee in part \(\displaystyle (a)\)?

 

[logistic_guy]

To warm up the audience, we give them the formula that will calculate the number of photons.

\(\displaystyle \frac{q}{E}\)

Simple and straightforward.