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In this lesson, we will learn how to calculate the imaging properties of reflecting, refracting, and compound optical systems used in telescopes.

Q1:

What is the angular magnification of a telescope that has a 100 cm-focal length objective and a 2.50 cm-focal length eyepiece?

Q2:

A 7.5x binocular produces an angular magnification of − 7 . 5 0 , acting like a telescope. (Mirrors are used to make the image upright.) If the binoculars have objective lenses with a 75.0-cm focal length, what is the focal length of the eyepiece lenses?

Q3:

A large reflecting telescope has an objective mirror with a 10.0-m radius of curvature. What angular magnification does it produce when a 3.00 m-focal length eyepiece is used?

Q4:

A planet at a distance of 1 0 1 2 m from Earth is observed by a telescope that has a focal length of the eyepiece of 1 cm and a focal length of the objective of 1 cm. The planet is seen to subtend an angle of 1 0 − 5 rad at the eyepiece. What is the size of the planet?

Q5:

Two stars that are 1 0 9 km apart are viewed by a telescope and found to be separated by an angle of 1 0 − 5 radians . If the eyepiece of the telescope has a focal length of 1.5 cm and the objective has a focal length of 3 meters, how far away are the stars from the observer?

Q6:

A telescope can be used to enlarge the diameter of a laser beam and limit diffraction spreading. The laser beam is sent through the telescope in the direction opposite to the normal one and can then be projected onto a satellite or the Moon. This is done with a telescope, producing a 3.50 m diameter beam of 630 nm wavelength light.

What is the minimum angular spread of the beam produced?

Neglecting atmospheric effects, find the size of the spot this beam would make on the Moon. Use a value of 4 . 0 0 × 1 0 8 m for the distance to the Moon.

Q7:

In a reflecting telescope, the objective is a concave mirror of radius of curvature 4.0 m and the eyepiece is a convex lens of focal length 6.0 cm. Find the apparent size of a 5.0 m tree at 20 km that you would perceive when looking through the telescope.

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