Einstei1 - Einsteins Box An amusing experiment on the...

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Einstein’s Box An amusing “experiment” on the equivalence of mass and energy is the following: consider a closed box with a flashlight at one end and light-absorbing material at the other end. Imagine the box to be far out in space away from gravitational fields or any disturbances. Suppose the light flashes once, the flash travels down the box and is absorbed at the other end. Now it is known from Maxwell’s theory of electromagnetic waves that a flash of light carrying energy E also carries momentum p = E / c . Thus, as the flash leaves the bulb and goes down the tube, the box recoils, like a gun, to conserve overall momentum. Suppose the whole apparatus has mass M and recoils at velocity v . Of course, v << c . Then from conservation of momentum in the frame in which the box was initially at rest: the recoil momentum of the box equals (minus) the momentum of the flash emitted. After a time
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This note was uploaded on 11/09/2011 for the course PHY PHY2053 taught by Professor Davidjudd during the Fall '10 term at Broward College.

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Einstei1 - Einsteins Box An amusing experiment on the...

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