A telescope is a device that is used to magnify distant objects with a relaxed e

Question

A telescope is a device that is used to magnify distant objects with a relaxed eye. One simple telescope is made of two converging lenses where the image from the front lens, called the objective, is the object for the back lens, called the eyepiece.

In 1655, just fifty years after Galileo’s first telescope, an astronomer named Christiaan Huygens used a selfmade telescope to discover that Saturn has a moon, which was later named Titan. Huygens used an objective lens that had an aperture of 35 mm and a focal length of 340 cm, with an eyepiece lens that had a focal length of 8.0 cm.

(a) What was the distance between the lenses?

(b) Starting with the diagram above, complete the ray diagram to show what happens inside the telescope tube in the diagram above. You do not need to draw the diagram to scale.

(c) Is the image virtual or real? Upright or inverted? Find the magnification of the image.

Explanation / Answer

a)

Given that

Huygens used an objective lens has a focal length of (fo) =340 cm=3.4m

The focal length of an eyepiece lens (fe) = 8.0 cm=0.08m.

The

The distance between the lenses is given by

L =fo+fe =340+8 =348cm =3.48m

c)

The magnification is given by

M =fo/fe =3.4/-0.08=-42.5

Therefore the magnification is negative, hence the image is virtual

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