Homework 3: Light and Telescopes

If the speed of light were twice its actual value, how far away would Vega be?

12.5 light‑years

Select the best definition for wavelength.

the distance between two crests of an electromagnetic wave

Select the best definition for frequency.

the rate at which electromagnetic waves oscillate

Consider a single photon with a wavelength of 𝜆, a frequency of 𝜈, and an energy of 𝐸.

What is the wavelength, frequency, and energy of a pulse of light containing 100 of these photons?

𝜆, 𝜈, and 100𝐸

Consider the relationship between the energy of electromagnetic radiation and its wavelength.

What will happen if the energy increases?

The wavelength will decrease

Consider the relationship between the energy of electromagnetic radiation and its wavelength.

What will happen if the wavelength increases?

The energy will decrease.

Arrange the different types of electromagnetic radiation by wavelength. Only include the items that are forms of electromagnetic radiation. From longest wavelength to Shortest

Radio waves

low frequency microwave radiation

high frequency microwave radiation

an orange photon

ultraviolet radiation

Select the correct statement comparing other regions of the electromagnetic spectrum to visible light.

The ultraviolet region of the electromagnetic spectrum has shorter wavelengths and higher frequencies.

Compared to visible light, microwaves

are less energetic

Compared to FM radio waves, X-rays

are more energetic

Compared to radio waves, sound waves

are not a form of electromagnetic radiation

A ray of light strikes a flat mirror at an angle as shown in the illustration. Note that, in this side‑view illustration, the mirror is laying flat on the ground. The arrow represents the direction that the incoming (or incident) ray of light is traveling and the angle at which it strikes the mirror.

Which of the illustrations represents the direction the ray of light is traveling after it reflects off the mirror? Note that, in each picture, the arrow represents a possible direction the ray of light could travel and the possible angle at which it leaves the mirror.

> 45 degree

The diagram shows parallel rays of light incident on a plane (flat) mirror. Note that, in this side-view drawing, the mirror is on the right, and the arrows represent the direction of three incoming (or incident) rays of light.

Which of the diagrams show the correct reflected rays for the mirror and incident rays given? Note that, in each picture, the arrows represents possible directions the three reflected rays of light could travel.

Up arrows

Identify two types of telescopes. The yellow lines show the path of light

first one( left one) is reflecting telescope (if picture shows it has a mirror in it.

Second one(right one) is refracting telescope

What property of a reflecting telescope determines its light‑gathering (or light‑collecting) power?

area of mirror

For each property, determine whether it applies to reflecting, refracting, or both telescope types.

Reflecting:

largest telescopes in the world

use a primary mirror

Refracting:

can be affected by chromatic aberration

use a primary lens

both:

collect and focus light

Select the reasons why most professional telescopes are reflectors rather than refractors.

Creating a flawless lens is difficult and very expensive.

It is easier to make a large reflecting telescope than a large refracting telescope.

Mirrors can be supported from the back.

Match the characteristics to the correct astronomical imager.

CCD:

Divided into array of pixel.

Used today in astronomy.

Image are saved directly in digital form.

Photographic plate:

must be developed with chemicals before image is analyzed.

Less sensitive to light.

Astronomers use adaptive optics to

correct for blurring from Earth's atmosphere in real time

Identify the true statements about the benefits of using space telescopes compared to Earth‑based telescopes.

Telescopes in space can observe wavelengths of light that are absorbed by Earth's atmosphere.

Space telescopes avoid atmospheric distortion by functioning above the Earth's atmosphere.

Just as optical astronomers observe the visible light emitted by objects such as stars and galaxies, radio astronomers can also observe the radio waves emitted by these objects, as well as the radio waves emitted by gas and dust. However, radio telescopes are different from optical telescopes in important ways.

In general, compared to optical telescopes, radio telescopes are

bigger

This is because

It is necessary to see fine detail.

Several radio telescopes are combined into an interferometer in order to

decrease the smallest angle which can be observed by the telescope.

Match each space telescope with a region of the electromagnetic spectrum that it primarily observes in. Some wavelengths may have more than one telescope.

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X‑ray:

Chandra observatory

Visible:

Hubble space telescope

Infrared:

Spitzer space telescope

Microwave:

None