Question

Billy is gearing up for summer! He gets his pitcher of ice tea, a good book, and sits out on the lounge chair in his yard for a lazy day reading under the sun. Unfortunately,he falls asleep and the UV light (avg wavelength 300nm) bombards his sleeping face, causing a painful erythema(also known as sunburn).Let’s consider the sunburning process for a 1.0cm diameter patch of Krochmal’s face.

a. The patch of skin needs to absorb about 5.5x10^15 photons of the ultraviolet light to cause reddening.How much energy does this correspond to?

b. The intensity(power per area) of UV light hitting Billy's face is about 0.002W/m2. Using this information, estimate for how much time Billy needs to lie in the sun to get sunburned. Give answer in minutes.

Answer 1