- #1
Achmed
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This is a follow-up to a question I asked earlier. We have the following exercise:
We have two parallel mirrors, which are located at y=0 and y=l in the (x,y) plane. A photon is traveling between the mirrors, up and down along the y-axis. Consider an observer O at rest w.r.t. the mirrors.
2. Using Galilean transformations from Newt. mech. , what's the time measured by O' for the photon to make a full period (draw a picture to illustrate the logic). Compare this with the time measured by O.
So for 1, the answer is [itex] \Delta t= \dfrac{2l}{c} [/itex]. I tried to do 2 too, but I keep getting a somewhat incorrect answer. Here's what I do:
Draw an isosceles triangle [itex]ABC[/itex] with [itex] |AB| = vt' [/itex], and the height is l. I figured that [itex] t' = \dfrac{2|AB|}{c'} [/itex], where [itex] c' = c-v [/itex]. So we try to solve the following equation: [itex] (c't')^2 = 4l^2 + (vt')^2 [/itex], but if I solve for t', I get an almost correct answer, which of course is still incorrect. You get [itex] t' = \dfrac{2l}{\sqrt{c^2-2cv}} [/itex], and of course we want [itex] t= \dfrac{2l}{c} [/itex] because in Newtonian mechanics t=t'. What have I done wrong?
We have two parallel mirrors, which are located at y=0 and y=l in the (x,y) plane. A photon is traveling between the mirrors, up and down along the y-axis. Consider an observer O at rest w.r.t. the mirrors.
- What's the time (Δt) measure by O for the photon to make a full period.
2. Using Galilean transformations from Newt. mech. , what's the time measured by O' for the photon to make a full period (draw a picture to illustrate the logic). Compare this with the time measured by O.
So for 1, the answer is [itex] \Delta t= \dfrac{2l}{c} [/itex]. I tried to do 2 too, but I keep getting a somewhat incorrect answer. Here's what I do:
Draw an isosceles triangle [itex]ABC[/itex] with [itex] |AB| = vt' [/itex], and the height is l. I figured that [itex] t' = \dfrac{2|AB|}{c'} [/itex], where [itex] c' = c-v [/itex]. So we try to solve the following equation: [itex] (c't')^2 = 4l^2 + (vt')^2 [/itex], but if I solve for t', I get an almost correct answer, which of course is still incorrect. You get [itex] t' = \dfrac{2l}{\sqrt{c^2-2cv}} [/itex], and of course we want [itex] t= \dfrac{2l}{c} [/itex] because in Newtonian mechanics t=t'. What have I done wrong?