According to quantum mechan i cs, electromagnetic rad iation of frequency v can be regarded as consisting of photons of energy hu where /i=6.626x 10-34 J.s is the Planck's constant.

(a) What is the frequency range of visible photons (400 nm to 700 nm)? What is the energy range of visible photons (both i n J an d i n eV)?

(b) How many photons per second docs a low power (1 mW) He-Ne laser (4=336 n m) em it? A cell phone that emits 0.4 W of 850 MHz radiation? A microwave oven operati ng at 2 GHz generati ng a microwave power of 1000 W? How many photons of the latter frequency have to be absorbed to heat up a glass of water (0.2 L, heat capacity of water 4.18 kJ.kt 1 .K-1 ) by 20 °C?

At a given power of an electromagneti c wave, do you expect a classical wave description to work better for radio frequ encies, or x-rays? Why? At what He-Ne laser power do you expect quantum effects to become important