Chapter 28, Focusing Light Video Solutions, Pathways to Astronomy

Problem 1

An image will appear upside down when we look through a simple refracting telescope, as can be seen from Figure 28.1 Trace the light through a similar diagram to show what orientation objects would have through a Cassegrain telescope. Assume the secondary mirror in the Cassegrain telescope is flat.

Sri Datta Vikas Buchemmavari

Numerade Educator

02:24

Problem 2

Suppose a reflector has a primary mirror with a diameter of $100 \mathrm{cm},$ and a secondary mirror that blocks a central region with a diameter of $25 \mathrm{cm}$. What fraction of the collecting area does the secondary mirror block? What would be the diameter of a telescope with the same collecting area if no part of its area were blocked?

Narayan Hari

Numerade Educator

03:45

Problem 3

The front surface of your eye (the cornea) does most of the focusing of light entering your eye; the back wall of the eye is like a focal plane. Draw a diagram similar to Figure 28.1 to show how your eye focuses the light rays from a distant star straight in front of you. Now draw light rays for a nearer point of light (a few times farther away from your cornea than the cornea is from the back of the eye). The light rays will be bent by the cornea by about the same angle as the distant starlight, so do they now focus closer or farther from the cornea? $A$ nearsighted person is able to focus on nearby objects, but not distant ones. What does this tell you about the shape of the cornea for a nearsighted person?

Farhanul Hasan

Numerade Educator

05:16

Problem 4

Most refracting telescopes have long telescope tubes, It should be possible to build a lens that focuses light much closer, with. out such a long tube. Sketch how the shape of the lens would need to be different for a lens that focuses closer. Use your diagram to show why such a close-focusing lens would probably have more severe problems with chromatic aberration.

Dading Chen

Numerade Educator

01:17

Problem 5

After the Palomar 5 -m telescope was completed, astronomers estimated that the mass of larger telescopes would increase as the (mirror diameter) $^{3}$ or (mirror diameter) $^{4}$ because of the greater mass of glass and support needed to keep the entire telescope stiff. If the 10 -m Keck telescopes followed this rule, how many times more massive would they have been than the Palomar telescope?

Prabhu Ramji

Numerade Educator

00:49

Problem 6

The index of refraction measures the factor by which light slows down in a substance. The index of refraction of water is 1.33 If you sent a pulse of light through water and a pulse of light through air (index of refraction of 1.00 ), how much longer would it take the light to travel $1 \mathrm{km}$ through the water? (The speed of light in air is $299,800 \mathrm{km} / \mathrm{sec}$.)

Mayukh Banik

Numerade Educator