Electrons are ejected with a maximum velocity of 5.1 x 10 5 m/s from a metal whe

Question

Electrons are ejected with a maximum velocity of 5.1 x 105 m/s from a metal when illuminated by photons with a wavelength of 440 nm. Calculate:

a. The energy of the incident photons.

b. The work function of the metal.

c. The longest wavelength of light which will result in electron emission.

Assuming it possible to travel at 0.95 c to a star at a proper distance of 100 light years from earth, calculate the following:

a. how long the trip to the star would take from the perspective of the traveler.

b. the distance between the earth and the star from the perspective of the traveler.

Explanation / Answer

a) E = hc/lambda = 1240/440 = 2.82 eV

b) KEmax = hf - work function

work function = 2.82-(1/1.6E-19)*0.5*9.11E-31*5.1E5^2=2.08 eV

c) max when hc/lambda = work

lambda = hc/work = 1240/2.08=596.2 nm

2)

first do b) 100 ly*sqrt(1-0.95^2)=31.22 ly

a) 31.22/0.95=32.86 years

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