# Light Refection and Snell's Law

The light beam shown in Figure P22.21 makes an angle of ϕ = 23.5° with the normal line NN' in the linseed oil. Determine the angles θ and θ'. (The refractive index for linseed oil is 1.48.)
The normal line makes a 90 angle with the surface of the linseed oil. The light then passes through water but I need the linseed oil angle to get the water angle.

Snell's Law

So I used 1*sin(23.5)=1.48*sin(theta) and solved for theta. I got 15.63 degrees which is incorrect

Kurdt
Staff Emeritus
Gold Member
If the angle is in the linseed oil then it is the angle after it has been refracted at the air linseed interface. Thats my guess anyway without seeing the diagram.

Redbelly98
Staff Emeritus
Homework Helper
Snell's Law

So I used 1*sin(23.5)=1.48*sin(theta) and solved for theta. I got 15.63 degrees which is incorrect

That equation works for an air-to-linseed oil interface or a vacuum-to-oil interface.

You have a water-oil interface; the refractive index of water must enter into Snell's law somehow.

Plus, use Kurdt's suggestion of putting the angle on the correct side of the equation :-)

Kurdt
Staff Emeritus