00:01
So we are told that there's a surface with a refractive index of n equals 1 .56.
00:07
And we want to find the angle of incidence such that the angle of refraction is half of the angle of incidence.
00:22
So in other words, the angle of incidence is two times the angle of refraction.
00:28
So let's set up our equation.
00:33
We know that that's equal to 1.
00:35
And our second medium is n2, which is just n.
00:39
So we'll have sine of theta 2.
00:43
We want to find what theta 1 is.
00:51
So we are going to say that sine of 2 of theta is equal to n sine of theta.
01:05
Now we're going to use the trigonometric identity to say that 2 sine theta to 2 -sign theta -cosine theta is equal to sine 2 -theta so we're going to replace that which will give us n -sign theta these two will cross off and that leaves us with cosine if we just told this algebraically we're going to get theta is equal to of course these are all theta 2s so we're going to end up with theta is equal to n over or rather the inverse cosine of n over 2 so that's going to give us 38 .7 degrees and of course theta 1 is twice that you know i think i just did this backwards actually i've made a mistake it's good that i caught myself here because theta 1 is equal to 2 theta 2...