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jegues
Mar10-11, 07:10 PM
1. The problem statement, all variables and given/known data

See figure attached for problem statement.

2. Relevant equations



3. The attempt at a solution

Using Snell's Law,

n_{1}sin(\theta_{1}) = n_{2}sin(\theta_{2})

n_{1} = \frac{n_{2}sin(\theta_{2})}{sin(\theta_{1})}

Where,

\theta_{1} = 30^{o}, \theta_{2} = 90^{o}

It gives me, n_{1} = 2 but the answer is a minimum of 1.15.

What did I do wrong/misunderstand?

tiny-tim
Mar11-11, 04:53 AM
hi jegues! :smile:

it's not 30°, it's 60° :redface:

jegues
Mar11-11, 08:39 AM
hi jegues! :smile:

it's not 30°, it's 60° :redface:

Yes I figured that much but I dont understand why.

I'm looking at the triangle and the angle at the bottom right should be 90-60 = 30, that's where the incident angle is isn't it?

tiny-tim
Mar11-11, 10:17 AM
hi jegues! :smile:
… the angle at the bottom right should be 90-60 = 30, that's where the incident angle is isn't it?

nooo :redface: … the angles of incidence and refraction are always from the normal :wink:

jegues
Mar11-11, 03:52 PM
hi jegues! :smile:


nooo :redface: … the angles of incidence and refraction are always from the normal :wink:

So a line perpendicular to the surface it's hitting, right?

tiny-tim
Mar11-11, 04:30 PM
s'right! :biggrin: