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if person A is outside a pool and person B is inside a pool with goggles, won't the light beam travel closer to the normal inside the pool but then away from the normal when it enters the goggles (due to air) so then the light beam appears to travel in a straight line (even though it zigzags?)

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  • $\begingroup$ Related: physics.stackexchange.com/q/4010 $\endgroup$ – Brandon Enright Nov 13 '14 at 6:47
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    $\begingroup$ It isn't clear what you mean by "appears to travel in a straight line". When you look at a mirror light has done some severe bouncing but the image in the mirror still looks normal. What does a "zigzag" look like? $\endgroup$ – Brandon Enright Nov 13 '14 at 6:48
  • $\begingroup$ @BrandonEnright like Floris' answer the second zigzag $\endgroup$ – MathApprentice Nov 13 '14 at 15:11
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The answer depends on the angle of the goggles with respect to the surface of the pool. What you say is true when the two are parallel, but you did not specify that. Otherwise the two water interfaces (with the air, and with the mask) will act like the (not parallel) faces of a prism, and the light will not return to the original direction inside the mask.

Simple diagram to clarify (not exact - and with rather high apparent refractive index):

enter image description here

On the left, the ray does not return to the same direction; on the right it does.

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