Find the index of refraction

1. May 31, 2007

AlanxD

1. The problem statement, all variables and given/known data
Suppose a convex lens is ground so that one surface has a radius of curvature of 30.0 cm and the opposing surface has a radius of curvature of 40.0 cm. The focal length is 34.2cm. What is the index of refraction of the lens? What kind of glass is the lens?

2. Relevant equations

Need help by using the formula
1/f=(n-1)(1/R1+1/R2).

3. The attempt at a solution

I knw R1=30 cm
R2=40 cm
f=34.2 cm
I cant finish finding n.

2. May 31, 2007

Stevedye56

What is meant by what type of glass is it? Is that supposed to mean if it is converging or diverging?

3. May 31, 2007

AlanxD

Like is it suppose to be crown glass, quartz, zircon, etc.
Can someone help solve the equation step by step and tell me what glass it is.

4. May 31, 2007

Stevedye56

Well using the formula given I got Crown Glass for the lens. Did you plug in the knowns into the equation?

5. May 31, 2007

AlanxD

Ya i did but can u type it step by step i knw how to plug it in the equation but i dun got that number.

6. May 31, 2007

Stevedye56

1/34.2=(n-1)(1/30 + 1/40)

.0313= (n-1)(.0333 + .0250)

.0313/.0583 = (n-1)

.537=n-1

n=1.54

Index of Refraction of Crown Glass 1.50-1.62

7. Jun 1, 2007

thanks alot.