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Thin Lens Problems

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Thin Lens Problems

87-88

The following data is from an experiment done with a thin converginglens. Use it to determine the image distance produced when the object is 25.0 cm from the same lens.

Givens:

do= 25.0 cm

Unknown:

di= ?

What do we need to find first?

First:

Equation:

The following data is from an experiment done with a thin converginglens. Use it to determine the image distance produced when the object is 25.0 cm from the same lens.

Givens:

do= 25.0 cm

Unknown:

di= ?

di= 14.0 cm

Equation:

Corrective lens prescriptions are given in “diopters.” A diopter is simply the reciprocal of the focal length of the lens (measured in meters). For example, a pair of reading glasses with a prescription of +2.25 would have lenses with focal lengths of 1/2.25 = 0.444 m. How tall would the image of a meter stick be if it were placed 75 cm from a pair of glasses with a prescription of -3.75 diopters?

Givens:

Equation:

do1= 75 cm = 0.75 m

prescription= -3.75 m

What do we need to find first?

Find f, in order to find di

ho= 1 m = 100 cm

Unknown:

f= -26 cm

hi = ?

Corrective lens prescriptions are given in “diopters.” A diopter is simply the reciprocal of the focal length of the lens (measured in meters). For example, a pair of reading glasses with a prescription of +2.25 would have lenses with focal lengths of 1/2.25 = 0.444 m. How tall would the image of a meter stick be if it were placed 75 cm from a pair of glasses with a prescription of -3.75 diopters?

Givens:

Equation:

do1= 75 cm = 0.75 m

prescription= -3.75 m

Find di

ho= 1 m = 100cm

f= -26 cm

Unknown:

di= -20 cm

hi = ?

Corrective lens prescriptions are given in “diopters.” A diopter is simply the reciprocal of the focal length of the lens (measured in meters). For example, a pair of reading glasses with a prescription of +2.25 would have lenses with focal lengths of 1/2.25 = 0.444 m. How tall would the image of a meter stick be if it were placed 75 cm from a pair of glasses with a prescription of -3.75 diopters?

Equation:

Givens:

do1= 75 cm = 0.75 m

prescription= -3.75 m

Solve:

ho= 1 m

f= -26 cm

Unknown:

Solution:

hi= 27cm

hi = ?

The human eye has a lens system that produces real images on the retina (1.7 cm in back of the lens). In order to focus on objects at a variety of distances from the eye, the lens must be able to change its focal length. What is the change in focal length of the eye’s lens system when you look up from a book 35 cm away to glance across a classroom 15 m away?

Givens:

Equation:

do1= 35 cm

What is finital?

do2= 15 m = 1500 cm

fi= 1.6 cm

di= 1.7cm

ffinal= 1.7cm

Unknown:

Δf= 0.1 cm

Δf = ffinal– finital =?

Two thin lenses, one a converging lens with a 14.0 cm focal length and the other a diverging lens with a 5.00 cm focal length are placed 18.0 cm apart. An object is placed 20.0 cm to the left of the converging lens (which is the closest lens). Determine the overall magnification.

Givens:

Equation:

do1= 35 cm

What is finital?

do2= 15 m = 1500 cm

fi= 1.6 cm

di= 1.7cm

ffinal= 1.7cm

Unknown:

Δf= 0.1 cm

Δf = ffinal– finital =?