A biconvex lens is made of glass whose index of refraction is 1.5. The lens has

Question

A biconvex lens is made of glass whose index of refraction is 1.5. The lens has a radius of curvature of 25cm for one surface and 49cm for the other.

Part A

Calculate the focal length of this lens as used in air.

Express your answer using two significant figures.

Part B

Calculate the focal length of this lens as used under water.

Express your answer using two significant figures.

A biconvex lens is made of glass whose index of refraction is 1.5. The lens has a radius of curvature of 25cm for one surface and 49cm for the other.

Part A

Calculate the focal length of this lens as used in air.

Express your answer using two significant figures.

fa = ____ cm  

Part B

Calculate the focal length of this lens as used under water.

Express your answer using two significant figures.

fw = ____ cm  

Explanation / Answer

a)

The focal length biconvex lens

1/ f = ( n -1) (1/ r1 - 1/ r2 )

= (1/5 -1 ) (1/ 25 cm - 1/ 49 cm )

f = 102.08 cm

WHen it is submerged in water

The focal length biconvex lens

1/ f = ( n -1) (1/ r1 - 1/ r2 )

= (1/5 -1.33 ) (1/ 25 cm - 1/ 49 cm )

f = 300.24 cm

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