Problem 25.34 An insect 1.1mm tall is placed 1.0mm beyond the focal point of the

Question

Problem 25.34

An insect 1.1mm tall is placed 1.0mm beyond the focal point of the objective lens of a compound microscope. The objective lens has a focal length of 12mm , the eyepiece a focal length of 30mm .

Part A

Where is the image formed by the objective lens?

Give your answer as the distance from the image to the lens. Express your answer using two significant figures.

s'1= __________ mm

Part B

How tall is the image mentioned in part A?

Express your answer using two significant figures.

y'1= __________mm

Part C

If you want to place the eyepiece so that the image it produces is at infinity, how far should this lens be from the image produced by the objective lens?

Express your answer using two significant figures.

d1= ________ mm

Part D

Under the conditions of part C, find the overall magnification of the microscope.

Express your answer using two significant figures.

M = __________

Explanation / Answer

Part A)

Apply 1/f = 1/p + 1/q

1/12 = 1/13 + 1/q

q = 156 mm but round to 2 sig figs and get...

q = 160 mm

Part B)

h'/h = -q/p

h'/1.1 = -156/13

h' = -13.2 mm tall

In two sig figs, that is 13 mm tall and inverted (so you may need the negative to signify the inverted)

Part C)

To form the image at infinity, you need to place the image at the focal point.

That is at 30 mm from the objective lens

Part D)

M = -25L/(fo)(fe)

L = 156 - 12 = 144 mm

M = -25(14.4)/(1.2)(3.0)

M = -100X (Again the negative means inverted)

Using two sig figs, that is M = 1.0 X 102 and you may need to include the negative for the inversion.

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