Yr 13 - Astrophysics & Cosmology (5.5.6 - 5.5.9)

Question 1

Isotropic

Answer 1

The same in all directions

Question 2

Homogeneous

Answer 2

Of uniform density

Question 3

Hubbles Law

Answer 3

Velocity = H0 x Distance

H0 (H naught) = Hubbles constant

Question 4

3 tests for big bang theory

Answer 4

• Galaxies should be moving apart as space expands
• CMB (cosmic microwave background) radiation from the big bang should be detected. (CMB is left over radiation from Big Bang)
• The light elements (H, He & Li) should have been made in the first minutes of the universe.
  (77% hydrogen, 23% helium, Lithium trace)

Question 5

What is CMB radiation?

Answer 5

Leftover radiation from the big bang.

Question 6

Electron Energy Level

Answer 6

A discrete energy that an electron must exceed to pass through or equal to remain on energy level.

Question 7

Ground State

Answer 7

Lowest electron energy level of an atom

Question 8

What happens to the energy when an electron goes down an energy state/s?

Answer 8

Energy is released as a single photon.

• Energy of photon is exactly equal to change in Ep of electron

Question 9

1 Electronvolt

Answer 9

Amount of energy transferred to an electron when passed through a PD of 1 volt.

Question 10

What happens when:

• An electron is exited
• An electron is de-exited (relaxed)

Answer 10

• Moves up energy levels
• Moves down energy levels

Question 11

What is the Lyman series?

Answer 11

Electron exited from any energy level other than Ground state down to ground state releases Ultraviolet light.

Question 12

What is the Balmer series?

Answer 12

Electrons exited from first energy level and relaxing back to first energy level releases visible light.

Question 13

What happens to electron at 0ev?

Answer 13

Electron no longer bound to atom & free to move.

Question 14

Energy levels only exist at certain energy levels therefore, they are …

Answer 14

Quantised.

• A quanta of energy Is a small indivisible amount of energy.

Question 15

When is the only time an electron is bound to the atom?

Answer 15

When it has energy equal to an energy level of the atom.

Question 16

Why are energy levels negative?

Answer 16

Because electrons must gain energy to move up or escape.

• 0ev is set for an escaped electron with 0Ek

Question 17

1 Parsec

Answer 17

Distance that gives parallax angle of 1 arc second.

Question 18

What determines the colour of emitted light?

Answer 18

The wavelength of the photon.

Question 19

How to convert ‘V’ to ‘eV’ and vice verse

Answer 19

V = ev x e

eV = V / e

e = Electron charge (1.6x10^-19_

Question 20

What is red shift or blue shift etc.

Answer 20

More of a certain energy given off by star.

Red shift = more low energy light given off (Red section of Emission line spectra is larger)

• Learn spectral class types for stars (section before this on Brainscape)

Question 21

E = hf but how do you calculate E from a energy level diagram?

Answer 21

E_Final - E_Initial = Change E

Question 22

Can electrons exist anywhere in the atom?

Answer 22

No, electrons can only exist at discreet energy levels (ones unique to the atom)

Question 23

What does the wavelength of the emitted photon depend on when an electron falls down an energy level?

Answer 23

Wavelength depends on energy difference between the 2 levels.

Question 24

Emission Spectra

Answer 24

Set of EM frequencies produced by exited atoms
- Visible as bright lines of spectra
- Each atom has a unique spectra representing its energy levels.

Question 25

Continuous Spectra

Answer 25

Spectra containing all visible EM frequencies (a composition of both emission & absorption spectra)
- Just colours and no lines

Question 26

Absorption Spectra

Answer 26

Set of EM frequencies absorbed by atom
- Shown as dark lines

Question 27

What spectra to hot objects emit?

Answer 27

Continuous as both absorption (of heat (infrared)) and emission (photons) which are both em frequencies.

Question 28

What is an astronomical unit?

Answer 28

Mean distance between earth and sun

Question 29

Parsec

Answer 29

Distance between SOL and astronomical object with parallax angle. (angle between SOL-object to star-earth)

Question 30

Next closest star to earth

Answer 30

Proxima Centauri

Question 31

Diameter of the Milky Way

Answer 31

1x10^5 ly

Question 32

Distance between milky way & nearest galaxy?

Answer 32

2.5x10^6 ly

Question 33

Describe the colours on the screen during the diffraction of white light

Answer 33

n = 0 - White light
n = +/- 1 - Blue closest to n=0 from both sides

Question 34

What is a maxima/minima

Answer 34

Maxima - two or more troughs/peaks of 2 or more waves superpose

Minima - Trough and peak of 2 or more waves superpose

Question 35

Weins displacement law

Answer 35

λMax = K / T

K = Weins Constant
T = Absolute Temperature

Question 36

What temperature must an object be above in order to emit em radiation?

Answer 36

> 0 Kelvin

Question 37

What is a black body

Answer 37

A body that absorbs all em radiation incident on it

• When in thermal equilibrium it emits a characteristic distribution of λ’s
• Can deduce temperature of black body by λ’s emitted.

Question 38

Luminosity

Answer 38

Total power radiated by a star (same as power)

Question 39

λMax

Answer 39

λ where the intensity is maximum

Question 40

Stephans Law

Answer 40

L = 4𝝅r^2𝛔T^4 (In equation booklet)