A helium-neon laser emits red light having a wavelength of 6.4 times 10^-7 m and

Question

A helium-neon laser emits red light having a wavelength of 6.4 times 10^-7 m and a power of 0.5 mW. How many photons are emitted each second? A photon whose energy is 8.00 times 10^-15 J is scattered off an electron at a 90 degree angle. What is the wavelength of the scattered wave? A photon whose wavelength is = 5.0 times 10^-11 m is scattered straight backward. What is the wavelength of the scattered wave? A neutron has a mass of 1.67 times 10^-27 kg. Its de Broglie wavelength is 1.4 x 10^-10 m. What is its kinetic energy (in eV)?

Explanation / Answer

The energy of a photon is given by the equation e = hc/

E is the energy ( 0.010 Joules per second because power of laser is given as 0.5mW )

h is Plank’s Constant ( value = 6.626 * 10^(-34) Joule Sec )

c is speed of light ( value = 3 * 10^(8) m/s ) (speed of light)

is wavelength of the light in metres (6.4 * 10^(-7) m )

Calculations :

E = 0.01 Joule per second. This is the Energy of all the photons emitted in one second.

So,

E = (no. of photons emitted per second) * (energy of one photon)

E = n * e

e = hc/

={ [ 6.626 * 10^(-34) ] * [ 3 * 10^(8) ] } / [ 6.4 * 10^(-7) ]

=3.313*10^(-19)

n = E/e = 0.01/3.313*10^(-19) = 3.01*10^(16)

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