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Chase11
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Homework Statement
A lens made of glass has one concave side with a radius of curvature of 5 cm, and one convex side with a raduis of curvature of 7.5 cm. What is the focal length of the lens? Is this a converging or diverging lens?
Homework Equations
nglass=1.5
nair=1.0
(1/f)=(n-1)[(1/R1)+(1/R2)
R1=5 cm
R2=7.5 cm
The Attempt at a Solution
1/f=(1.5-1)[(1/5cm)+(1/7.5cm)] = .5(7.5cm+5cm/.375cm) = 16.667
So f=1/16.667=.06cm
The answer is supposed to be -30 cm and diverging. I have done a lot of similar problems right, I don't understand what I keep doing wrong on this one.