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Homework Statement
A laser emits a monchromic beam of wavelength λ, which is reflected normally from a plane mirror, receding at a speed v. What is the beat frequency between the incident and reflected light?
Homework Equations
The Attempt at a Solution
The solutions starts off with this
[itex]f_{1} = \frac{f_{0}}{1 + \frac{v}{c}}[/itex]
But I'm not exactly sure where this equation came from. The solution uses
[itex]f_{0}[/itex] frequency of source
[itex]f_{1}[/itex] frequency of incident light (source) as measured by moving mirror
[itex]f_{2}[/itex] frequency of reflected light as measured by the moving mirror
I know that the Doppler effect is often stated as
[itex]\frac{λ^{'}}{λ} = \sqrt{\frac{1 - \frac{v}{c}}{1 + \frac{v}{c}}}[/itex]
So I'm not exactly sure where the first equation came from. Thanks for any help.