Astronomy and cosmology

Question 1

Luminosity

Answer 1

Total power of radiation emitted by a star

Question 2

Standard candle

Answer 2

Astronomical object which has a known luminosity due to a characteristic quality possessed by that class of object

Question 3

example of a standard candle

Capheid variable stars def

Answer 3

pulsating star which increases and decreases brightness over time

Question 4

Example of a standard candle

Type 1a supernova

Answer 4

a supernova explosion involving a white dwarf

Question 5

Inverse square law

Answer 5

Radiant flux density, F, is indirectly proportional to the square of distance

F=L/4πd²

Question 6

How are standard candles used to determine distance

Answer 6

Standard candles luminosity can be compared to other objects to understand their distance from the Earth.

inverse square law can be used for calculation

Question 7

Wien’s displacement law

Answer 7

wavelength of maximum intensity is inversely proportional to (thermodynamic) temperature

colour-frequency- wavelength is influenced by temperature

Question 8

Stefan Boltzman law

Answer 8

Total energy emitted by a black body per unit area per second is proportional to the fourth power of the absolute temperature of the body

E/At = σ x T4

Question 9

What can be used to find increase/ decrease in wavelength

Answer 9

Difference in lines of emission spectra

Question 10

Red shift

Answer 10

when emission spectro lines move to the right

Question 11

Explain why the red shift explains that the universe is expanding (3)

Answer 11

• receding stars or galaxies
• space between the earth and galaxies expand
• universe is expanding

Question 12

Hubble’s law

Answer 12

the recession speed of the galaxies moving away from the Earth is directly proportional to their distance from the Earth

Question 13

Big bang explained

Answer 13

• if the universe is expanding, at some point in time, it started as an extremely hot, dense, singular point which subsequently began expanding very quickly

Question 14

SI unit of luminosity

Answer 14

Watts

Question 15

Radiant flux intensity def

Answer 15

the observed amount of intensity of the radiant power per unit area of radiation measured on earth

Question 16

Cosmic distance ladder meaning

Answer 16

A large picture of the scale of the universe built by collecting data measurements

Question 17

What is a black body

3 points

Answer 17

• absorbs all incident em radiation falling on it
• does not reflect/ transmit any radiation
• has a characteristic emission spectrum that depends on its thermodynamic temperature

Question 18

What does the intensity- wavelength graph depend on

Answer 18

temperature,
I∝T
λ∝1/T

Question 19

What does the colour of the star depend on

Answer 19

Surface temperature

Question 20

Hottest stars are what colour

Answer 20

Bluish white

Question 21

Cooler stars are what colour

Answer 21

Deep shade of red

Question 22

What does the luminosity of a star depend on

2 points

Answer 22

• surface temp, T
• radius, r

Question 23

Difference between radiant flux intensity and luminosity

Answer 23

Radiant flux intensity is the amount of radiation measured on earth whereas luminosity is the total radiation that leaves the star