Chapter 5 - Chapter 6

Question 1

What causes the changes in tides?

Answer 1

The differential gravitational force from the Moon stretched the Earth, raising symmetric tidal bulges.

Question 2

What do tides affect?

Answer 2

Tides affect both water and land, but since water flows more readily we mostly observe changes in water level

Question 3

two tidal bulges model?

Answer 3

1. take the total gravitational force from the moon
2. Differential gravitational force from the moon (subtract the average force)
   This causes the water to rush to locations along the Earth-moon axis. to add to this the earth is also rotating

Question 4

How does Earth’s rotation affect the two tidal bulges model?

Answer 4

Earth’s rotation causes friction. Friction pulls the tidal bulges slightly below the Earth and Moon axis.

Question 5

What about the Moon’s tides?

Answer 5

Moon is smaller, so the difference in force between the Earth-side and far side is smaller. Also no easily moved water on the moon.

Question 6

What forces affect tides and the moon?

Answer 6

The moon’s gravity on earth’s tidal bulges acts as a torque to change the Earth’s angular momentum. In the past the Moon rotated faster, causing a similar misalignment of its tidal bulges.

Question 7

How did earths forces affect the moons rotation?

Answer 7

Torque from the Earth’s gravity slowed the Moon’s rotation and locked into synchronous rotation. Once the Moon’s rotation slowed enough that it was equivalent to its orbital period, the bulges are now perfectly aligned, so no further slowing occurs

Question 8

What are two properties of Light?

Answer 8

1. Light behaves like a wave, creating an interference pattern.
2. Under other circumstances it behaves like individual particles (photons)

Question 9

Wavelength vs frequency?

Answer 9

wavelength is the distance between peaks. Frequency is the number of times each second that the electric (and magnetic) field vibrates up and down at any point.

Question 10

Wavelength formula

Answer 10

lamda * f = c
lamda is wavelength
f is frequency
c is the speed of light

Question 11

Light as a Photon

Answer 11

light also behaves as a particle called a photon. Each photon carries a tiny fixed amount of energy proportional to its frequency.

Question 12

Energy formula

Answer 12

E = hf
E = h(c/f)
h is Planck’s constant
E is the photon energy in joules or EV

Question 13

The Electromagnetic Spectrum

Answer 13

gamma rays, x-rays, ultraviolet, visible, infrared, microwave, and radio. (shorter wavelength = highest energy and highest frequency)

Question 14

How does matter interact with light?

Answer 14

matter emits light.
matter absorbs and reflects light.
matter transmits light.

Question 15

What is a spectrum

Answer 15

A spectrum is a plot showing how much light is emitted at each wavelength

Question 16

2 laws of thermal emission

Answer 16

1. A hotter object emits more light per unit surface area than a cooler object at all wavelengths
2. the peak wavelength is shorter (bluer)for hotter objects and longer (redder) for cooling objects.

Question 17

What is Wein’s Law?

Answer 17

hotter temperature objects have their peak emission at smaller wavelengths. (therefore are blue)

Question 18

Why is the sun white?

Answer 18

the sun’s peak wavelength is green but it emits all of the colours of visible light looking white.

Question 19

Why is the sky blue?

Answer 19

Air molecules in Earth’s atmosphere scatter shorter wavelengths, Blue and purple light bounces around the atmosphere before reaching us

Question 20

transitions from one energy level to another

Answer 20

energy level refers to the amount of KE and PE of an electron. Transitions require the exact amount of energy. photons passing through (wavelength) can excite a transition.

Question 21

What do absorption line spectra show?

Answer 21

absorption lines spectra show where the light of a specific wavelength has been absorbed

Question 22

What do emission line spectra show?

Answer 22

Emission line spectra show us where lines at specific wavelengths are emitted

Question 23

How are emissions and absorption spectra linked?

Answer 23

Emission and absorptions lines occur at the same wavelength for the same element/molecule

Question 24

But light waves also undergo the doppler effect

Answer 24

Redshift: object is moving, Rest Frame: object is at rest relative to us. Blueshift: object is moving towards us.

Question 25

When does the doppler effect happen

Answer 25

Only when it is in line with where you are standing

Question 26

Classical Doppler Shift Formula

Answer 26

((delta)lamda)/ lamda = v/c
(Delta)lamda) = shift in wavelength
lamda = rest wavelength
v = velocity of the emitter
c = speed of light

Question 27

Why is the Doppler shift important

Answer 27

We measure the Doppler shift in stellar spectral absorption lines to determine the star’s velocity of about the center of mass.

Question 28

Two main properties of a telescope

Answer 28

1. Collecting Area: how many photons can it collect per second?
2. Resolution: how crisp of an image can it produce?
   Both depend on the size of the telescope, for telescopes, “size” = “diameter of primary optic”

Question 29

What is the angular separation

Answer 29

we can distinguish that there are two stars, not just one

Question 30

The diffraction limit

Answer 30

because of the diffraction of light, the best possible angular resolution for a telescope is related to the wavelength of light and the size of diameter of the telescope

Question 31

Angular Resolution of smaller/larger telescopes

Answer 31

Larger telescopes have better angular resolutions

Question 32

What is the link between wavelength and telescopes?

Answer 32

Different wavelengths show us different features

Question 33

What about magnification?

Answer 33

We can use additional lenses to control the magnification and field of view of the image. But, just like zooming, you can’t get past the resolution limit.

Question 34

Refracting Telescope?

Answer 34

Refracting telescope: Use lenses to focus light.
- Lenses were easier to make therefore the refracting telescopes were first.
- Refractors are very long since light follows a fairly straight path through them.
- Lenses very large are very impractical (super heavy)

Question 35

Reflection Telescope?

Answer 35

Reflective telescope: Use mirrors to focus light.
- Mirrors are made of glass with a thin coating.
- Since the light path can reflect back and forth, these don’t need to be as long.
- Large modern telescopes are reflectors.
- Also sag under their own weight, or due to temperature/wind
- Largest telescopes are segmented
- Solution is to build smaller segments and use computers, sensors, and motors to control their shape.