Question

CalcuLate the velocity of an electron ejected if 300.0 mm of light is applied to the surface. A wavelength of 795 nm has sufficient energy to eject electrons.

Answer 1

The equation relating velocity and wavelength is written below:

v = λf
where λ is the wavelength in m while f is frequency in 1/s.

Let's determine first the frequency from the speed of light:
c = distance/time, where c is the speed of light equal to 3×10⁸ m/s
3×10⁸ m/s = (300 mm)(1 m/1000 mm)/ time
time = 1×10⁻⁹ seconds
Since f = 1/t,
f = 1/1×10⁻⁹ seconds = 10⁹ s⁻¹

Thus,
v = (795×10⁻⁹ m)(10⁹ s⁻¹)
v = 795 m/s