Internal Reflection and Snell's Law TPR FL 1 Spoiler

[betterfuture]

Can someone explain this

I totally guessed on this but I still want to know how do I figure this out. I know that internal reflection occurs when the medium has an index of refraction greater than the other medium. But what I don't understand it what results when that same medium is put into another fluid and how that affects the critical angle. Thanks!

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[salemstein]

Well, you know that the crit angle is arcsin n(small)/n(large). n(small) used to be 1, then increased to some value between 1 and n(large). Since the fraction increases, so would arcsin.

 

[betterfuture]

But how can the index of refraction change? Isn't it a constant, so it's not supposed to change?

 

[theonlytycrane]

Imagine some object with index of refraction n. Light going from the object to the air (measured from the inside) can undergo total internal reflection since n > n(air).

Using snell's law: nsin(theta1) = n(air)sin(theta2). In TIR, sin(theta2) = 1 and theta1 = sin_inverse(n(air) / n).

Putting the object in fluid still requires measuring from the inside since n > n(fluid), but now the light goes from the object to fluid instead of air so the equation above gets n(air) replaced by n(fluid). The result is a larger theta1, which is the critical angle.

 

[aalamruad]

Imagine some object with index of refraction n. Light going from the object to the air (measured from the inside) can undergo total internal reflection since n > n(air).

Using snell's law: nsin(theta1) = n(air)sin(theta2). In TIR, sin(theta2) = 1 and theta1 = sin_inverse(n(air) / n).

Putting the object in fluid still requires measuring from the inside since n > n(fluid), but now the light goes from the object to fluid instead of air so the equation above gets n(air) replaced by n(fluid). The result is a smaller theta1, which is the critical angle.

Don't you mean that the result is a larger theta1 and thus a larger critical angle? Everything you said sounded solid except that last sentence, I believe. Since n(air) is replaced by a larger value, the critical angle will be larger too.

 

[theonlytycrane]

@walloobi yes! Thanks for the catch

 

[betterfuture]

Y'all are killing it with the good splainin'! Thanks everyone who helped!