Question

In the 2007 film I Am Legend, there is a scene in which Robert Neville (played by Will Smith) and his dog Sam are being pursued by some infected dogs, who are held off by a beam of light across their path. In this film, sunlight hurts the infected, so they avoid it. However, it seems that the fluorescent light that Neville uses in his lab does not harm them. Fluorescent bulbs emit light at wavelengths of 551 ?? and 623 ??, which together give the appearance of yellow-white light. Daylight has a peak emission wavelength at 460 ??.

1. Some fluorescent bulbs are filled with Mercury vapor, which produces the given emission lines. Both of these are transitions from or to the ? = 97 level in mercury. Identify both transitions.

2. The infected seem to burn in a way similar to sunburns, but faster. The average person is most prone to sunburns from UV rays with wavelengths in the 265 − 275 ?? range. Instead, the infected seem to be most susceptible to our peak daylight emission. Find the energy difference between the peak daylight wavelength and this UV wavelength (just use 270 ??).

Answer 1

Enegy of a electromagnetic wave having wavelength lambda E=hc/lambda

Where h is plank constant h=6.63*10^(-34) js

C is velocity of light=3*10^8 m/s

Peak dayligth wavelength is 460nm

So correspoinding energy E=6.63*10^(-34)*3*10^(8)/(460*10^(-9))

E=4.32*10^(-19)j

UV wavelength is 270nm

So correspoinding energy

E'= 6.63*10^(-34)*3*10^(8)/(270*10^(-9))

E'=7.37*10^(-19)j

So the energy difference ΔE=E'-E=3.05*10(-19)j

Or 1eV=1.6*10(-19)j

Therefore 3.05*10(-19)j =3.05/1.6 eV =1.9eV