How Do You Calculate the Index of Refraction for a Lens?

[AlanxD]

Homework Statement

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?

Homework Equations

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

The Attempt at a Solution

I knw R1=30 cm
R2=40 cm
f=34.2 cm
I can't finish finding n.

 

[Stevedye56]

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

 

[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.

 

[Stevedye56]

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

 

[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.

 

[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

 

[AlanxD]

thanks alot.