physics I need help!?

Question

17) what is the intensity of the electromagnetic radiation at a distance of 2.00 m from a 100 W isotropic source?


18) A light ray in air strikes a glass surface with an angle of incidence of 30 degrees. The angle of refraction in the glass is 20 degrees. What is the index of refraction of the glass?

please help and explain to me how to do these problems, I am having a hard time and I have a crappy book that doesn't help me at all!!! thanks

Answer 1

17) what is the intensity of the electromagnetic radiation at a distance of 2.00 m from a 100 W isotropic source?

Divide the Energy/area

First find the surface area of a sphere: 4pi*r^2 in meters

therefore Energy/area= 100W / (4pi*(2m)^2)
=3.98 W/m^2


18) A light ray in air strikes a glass surface with an angle of incidence of 30 degrees. The angle of refraction in the glass is 20 degrees. What is the index of refraction of the glass?

This is Snell's law where
Sin(theta-air)/Sin(theta-glass) = Index glass/Index air
therefore Index glass= Sin Air*Index Air/Sin Glass
=.50*1/.34
=1.46

For a better explanation see:
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

and

http://theory.uwinnipeg.ca/physics/light/node5.html#SECTION002240000000000000000