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Discussion Response Post to: irodov

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edison (8935)

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The problem reads as

Q) Demonstrate thet a light beam reflected from three mutually perpendicular plane mirrors in succession reverses its direction.

Sol) Choose the unit vectors perpendicular to the mirror as the x, y, z axes in space. Then after reflection from the mirror with normal along x axis

e ' = e - 2 i (i . e) = -e_x i + e_y j + e_z k

where i, j, k ar basic unit vectors.

After a second refelection from the 2nd mirror say along y axis.

e'' = e' - 2j (j.e) = -e_x i - e_y j + e_z k

Finally after the third reflection

e''' = -e_x i - e_y j - e_z k = -e.

A paradox is an argument that starts with apparently acceptable assumptions and leads by apparently valid deductions to an apparent contradiction. Since logic admits no contradictions, either the apparently acceptable assumptions are not acceptable, or the apparently valid deductions are not valid, or the apparent contradiction is not a contradiction. A paradox moves us to reexamine the argument until we find out what is wrong.

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