If the wavelength of microwaves in the oven is 9.75 cm, how long does it take, and determine the numbers of photons must be absorbed, to make the water boil? A certain microwave oven delivers 671 watts (J/s) of power to a coffee cup containing 32.8 g of water at 25°C. The specific heat capacity of water is 4.18J/°C·g.