# Homework Help: Simple glass lens

1. Nov 1, 2009

### songoku

1. The problem statement, all variables and given/known data
A simple glass lens do not focus the image of an object correctly under white light because

a. the lens absorbs light
b. the glass has come colouration due to impurities
c. the surface of the lens reflect some light
d. a glass prism splits sunlight into different colours.
e. glass absorbs UV light

2. Relevant equations

3. The attempt at a solution
Sorry I am clueless....

2. Nov 1, 2009

### rl.bhat

Glass lens focuses light due to refraction. Refractive index depends on the color of the light. That is why we see the rainbow. In the lens the colors in the white light are brought to focus at different points producing a blur image.

3. Nov 2, 2009

### songoku

Hi Mr. rl.bhat
You mean the refractive index of one glass lens depends on the color of the light that passes through it?

This is what I can come up with :

$$n=\frac{c}{v}$$ , where v is the speed of light in medium

The speed of red light and blue light will be different if they travel in same medium (e.g water) so the value of n (refractive index) of the water will be different for them?

And they only have the same speed if they travel in vacuum?

I think the answer is (d)

Thanks