1.An owl has good night vision because its eyes can detect a light intensity as
ID: 2020705 • Letter: 1
Question
1.An owl has good night vision because its eyes can detect a light intensity as small as 5.0 x 10-13 W/m2. What is the minimum number of photons per second that an owl eye can detect if its pupil has a diameter of 8.2 mm and the light has a wavelength of 552 nm?2.The work function of a metal surface is 4.80 x 10-19 J. The maximum speed of the electrons emitted from the surface is vA = 7.8 x 105 m/s when the wavelength of the light is ?A. However, a maximum speed of vB = 5.7 x 105 m/s is observed when the wavelength is ?B. Find the wavelengths ?A and ?B.
Explanation / Answer
W = 4.80 x 10-19 J. vA = 7.8 x 105 m/s, vB = 5.7 x 105 m/s, find A and B
hc/ = W + mv2/2
= 2hc/(2W + mv2)
A = 2hc/(2W + mvA2) = 263 nm
B = 2hc/(2W + mvB2) = 317 nm
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