The objective and the eyepiece of a microscope have focal lengths of 4.0 mm and

Question

The objective and the eyepiece of a microscope have focal lengths of 4.0 mm and 25 mm, respectively. The objective produces a real image 30 times the size of the object. The final image is viewed at infinity. The near point of the microscope user is at 25 cm. 1) What is the distance between the object and the focalpoint of the objective, in mm? 2) What is the overall magnification of the microscope?

The answers are 1) .13 and 2) 300 but I cannot figure out how it is calculated/formula used, etc.

Please help! Thanks.

Explanation / Answer

Part 1)

From the previous question I solved for the image distance, you remember that the object distance P, was 4.133 mm

From

1/4 = 1/p + 1/30p

p came out to be 4.133 mm

Since the focal length is 4 mm

4.133 - 4 = 1.33 mm

Part 2)

The Mo of the objective was already given as 30

The m of the eyepiece for a microscope is found by the formula

me = 25cm/fe = 25cm/2.5cm   (25 mm focal length = 2.5 cm) = 10

Total magnification is Mome = (30)(10) = 300

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