Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42mW.
Find the energy and momentum of each photon in the light beam.

Explanation

Wavelength, `lamda = 632.8 nm = 632.8 xx 10^(-9)m`
`:.` Energy of each photon,
`E = (hc)/(lamda) = (6.626 xx 10^(-34) xx 3 xx 10^(8))/(632.8 xx 10^(-9))`
`= 3.14 xx 10^(-19)J`
and momentum,
`p = (h)/(lamda) = (6.626 xx 10^(-34))/(632.8 xx 10^(-9))`
`= 1.05 xx 10^(-27) kg.m.s^(-1)`