# Can the angle of refraction be equal to the angle of incidence?

1. Jun 26, 2009

### bobaustin

Snell's law says
n1sin(theta1) = n2sin(theta2)

The angle of refraction theta2 can be greater or less than the angle of incidence theta1. That's fairly obvious.

My question is if theta2 = theta1 then we don't have an interface (because n1 = n2) so the light is still in the same medium, and there is nothing to talk about???

Is there a case where there is an interface and theta2 = theta1 ?

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I think I found the answer: Pyrex rod in Wesson oil!

Last edited: Jun 26, 2009
2. Jun 26, 2009

### Staff: Mentor

You can always pretend that there's an interface, with each side having the same n. Snell's law then tells you that θ1 = θ2, which makes sense since it just means that the light continues straight through as if there was no interface (which there isn't, of course).

3. Jun 26, 2009

### ideasrule

How about the case that the OP pointed out: two transparent substances with the same index of refraction?

Of course, angle of incidence is also equal to the angle of refraction with the former is 90 degrees.

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