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# Rotation of plane mirror

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With a fixed incident ray, if a plane mirror is rotated through an angle theta about an axis lying in the plane of incidence, what is the angle through which the reflected ray will rotate?

I think the reflected ray will not rotate at all because the axis of rotation is perpendicular to the plane of the mirror. This means that mirror will be rotating in its own plane. Is my understanding right?

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axis of rotation is in the plane of incidence, this is the plane created by the incoming beam, you may want to check your reasoning :)

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if you wanna dig deep, i think that photons hitting a rotating mirror will expereience some doppler's shift due to somethings about it's momentum....

well as for the question, it should obey the law:

angle of incidence=angle of reflection

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It depends on which of the possible axes in the plane of incidence, and the answer would have to be worked out differentially.

i think that photons hitting a rotating mirror will expereience some doppler's shift
Wow, how about a quantitative analysis?
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Angle of incidence = Angle of reflection.

Rotate the mirrior by theta, the angle of incidence increases by theta. So does the angle of reflection.

Hence the reflected ray rotates by two times theta.

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Not for an axis lying in the plane of incidence, Ron. Before replying, I read the first post again, a bit more carefully. ;)

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Not for an axis lying in the plane of incidence, Ron. Before replying, I read the first post again, a bit more carefully. :eek:

Oho! Oh, yeah. Oh yeah.

He's right then...

Sorry geocentric.

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Oho! Oh, yeah. Oh yeah.

He's right then...

Sorry geocentric.

Thats fine.

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Wow, how about a quantitative analysis?

thinking about how the rotation of the mirror affects space-time... hmmm, too complicated. actually i was thinking about something similar to compton's effect. the derivation should be similar.

light reflected naturally obeys the equation described by compton. a photon that is 90 degrees incident to the mirror should experience a wavelength shift of 2*compton wavelength...

perhaps i will try to work on it tomorrow.

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