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A level Physics > Unit 1.6 - Using radiation to investigate stars > Flashcards

Unit 1.6 - Using radiation to investigate stars Flashcards

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1
Q

What do stars constantly emit?

A

A continuous spectrum of radiation

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2
Q

Where does the continuous spectrum of radiation from a star come from?

A

The dense gas of the surface of the star

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3
Q

Describe the atmosphere of the star’s atmosphere

A

Tenuous - the star’s atmosphere is a lot less dense than the gases forming in the surface

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4
Q

What do gases in the star’s atmospheres do?

A

Absorb certain wavelengths of light

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5
Q

What’s responsible for certain wavelengths of light being absorbed?

A

Atoms in the gases of the stars atmosphere

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6
Q

What causes absorption lines on the line absorption spectrum?

A

Atoms in the gases of the star’s atmosphere absorbing certain wavelengths of light

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7
Q

At what end of the electromagnetic spectrum is the wavelength shortest?

A

The red, gamma end

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8
Q

What’s the phrase for the unaffected spectrum of light emitted from stars?

A

Continuous spectrum

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9
Q

What does our brains interpret as white?

A

A mixture of colours from the continuous spectrum

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10
Q

What do you call the spectrum with the black lines?

A

Line absorption spectrum

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11
Q

What do the lines on the line absorption spectrum represent?

A

Certain wavelengths of light bring absorbed by gases in the stars atmosphere

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12
Q

What would the black line on a line absorption spectrum show on a graph?

A

A dip

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13
Q

What does a dip in a graph/a black line on the line absorption spectrum mean in terms of electrons?

A

Less of them

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14
Q

What’s the phrase for the line absorption spectrum from our sun?

A

Fraunhofer spectrum

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15
Q

What is wavelength measured in?

A

nm

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16
Q

Black bodies

A

Bodies which absorb all the electromagnetic radiation that falls upon it

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17
Q

What can no other bodies compare to black bodies with?

A

No body is a better emitter of radiation at any wavelength than a black body

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18
Q

What are good approximations of black bodies? Why?

A

Stars as they’re perfect “emitters” of electromagnetic radiation

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19
Q

What does the intensity of radiation emitted from a black body vary with?

A

The wavelength

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20
Q

What does wavelength vary for black bodies?

A

The intensity of the radiation emitted

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21
Q

What does a higher temperature mean for a black body curve on a graph?

A

-Higher peak intensity
-Lower peak intensity wavelength (shifted to the left)

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22
Q

What colour would hotter stars appear?

A

Blue

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23
Q

What would a lower temperature show on a black body graph?

A

A longer “flat” section before the curve “lifts off”

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24
Q

What do you call the curves on the black
body graphs?

A

Black body curves

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25
Q

What goes along the x and y axes on a black body graph?

A

x - wavelength
y - spectral intensity

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26
Q

What does Wien’s displacement law state?

A

The wavelength of peak emission from a black body is inversely proportional to the absolute (kelvin) temperature of the body

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27
Q

What does ŷ(upside down)max mean in Wien’s displacement law?

A

Wavelength of peak emission (m)

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28
Q

What does T mean in Wien’s displacement law?

A

Absolute temperature (K)

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29
Q

What does W mean in Wien’s displacement law?

A

The Wien constant

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30
Q

How do you figure out the temperature in Kelvins from °C?

A

Whatever it is in °C, plus 273.15

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31
Q

When is the energy of particles in a body the lowest it can be?

A

At 0K (-273.15°C)

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32
Q

What happens at 0k (-273.15°C)?

A

The energy of particles in a body is the lowest it can be

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33
Q

What did Stefan’s law state?

A

The total electromagnetic radiation energy emitted per unit time by a black body is given by…(the formula)

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34
Q

What does the P stand for in Stefan’s law? (+units)

A

Power (W)

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35
Q

What does the A stand fit in Stefan’s law? (+units)

A

Surface area of the black body (m2)

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36
Q

What does the o stand for in Stefan’s law?

A

The Stefan constant

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37
Q

What does the T stand for in Stefan’s law? (+units)?

A

Absolute temperature (K)

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38
Q

Luminosity of a star

A

The total energy it emits per unit time in the form of electromagnetic radiation

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39
Q

What’s luminosity measured in? What does this mean?

A

Watts
Luminosity = power

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40
Q

What does the fact that luminosity is power mean?

A

We can use Stefan’s law to calculate it

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41
Q

What does the inverse square law state? Why is this?

A

Less energy strikes each square metre of a surface per second as the distance from a light source increases
- Spread out over a larger “surface area”

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42
Q

Intensity

A

The amount of light energy striking each metre square per second

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43
Q

Intensity formula

A

I = P
—
4(pi)R2(little 2)

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44
Q

What does I stand for in the intensity formula (+units)?

A

Intensity of the radiation (Wm-2)

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45
Q

What does the P stand for in the intensity formula (+units)?

A

Total power (luminosity) from the star (W)

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46
Q

What does the R stand for in the intensity formula (+units)?

A

Distance from the star (m)

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47
Q

What does the 4piR2 represent in the intensity formula?

A

The surface area of an “imaginary” sphere radius of R

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48
Q

Multi wavelength astronomy

A

Studying stars by observing areas outside the visible light spectrum gives information on processes that took place

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49
Q

What’s an example of multi wavelength astronomy revealing something big?

A

Observing the microwave region of the spectrum revealed cosmic microwave background radiation (CMBR)

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50
Q

What does multi wavelength astronomy require and why?

A

Different telescopes that are sensitive to different wavelengths in the electromagnetic spectrum in order to get information on processes that took place

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51
Q

Why are colours in astronomy considered “false colours”? What’s the exception?

A

They’re used as an “intensity code”, not as actual colours
Visible light is an exception

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52
Q

What type of telescope do we use to observe visible light?

A

An optical telescope

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53
Q

List the types of electromagnetic radiation on the E-M spectrum in order of wavelength, starting from the longest wavelength

A

Radio
Micro
Infrared
Visible
Ultra violet
X-ray
Gamma

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54
Q

What range of wavelength are we able to see?

A

700nm-400nm

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55
Q

What does the electromagnetic spectrum show (+units)?

A

Wavelength (m) and Frequency (Hz)

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56
Q

Wave speed formula

A

c = y(upside down)f

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57
Q

What does c stand for in the wave speed formula (+units)?

A

Wave speed (m/s)

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58
Q

What does the upside down y stand for in the wave speed formula (+units)?

A

Wavelength (m)

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59
Q

What does f stand for in the wave speed formula (+units)?

A

Frequency (Hz)

60
Q

What does energy do to an electron?

A

Excited electrons to lift them up the states

61
Q

What excites electrons to lift them up the states?

A

Energy

62
Q

What are the different states an electron travels up?

A

Infinity level
(etc)
3rd excited state
2nd excited state
1st excited state
Ground state

63
Q

What happens when the electron reaches the infinity state?

A

It leaves the atom to become an ion

64
Q

What happens to the excitement states as they increase?

A

Get closer

65
Q

What does the gap between each excitement state of an electron represent?

A

A quantum - a quantity of energy proportional to the frequency of radiation it represents

66
Q

What happens when a wavelength corresponds to an exact quantum?

A

When it corresponds to this exact energy jump, the photon disappears, the electron jumps an energy state and the photon randomly reappears

67
Q

What does a black line represent on the line absorption spectrum in terms of electrons?

A

Less there

68
Q

What does shorter wavelength mean in terms of energy?

A

More energy

69
Q

What does more energy do for the electrons in the excitement states?

A

Higher jumps = more blue

70
Q

What does the line absorption spectrum allow us to do?

A

Recognise gases in the stars’ atmospheres (look for oxygen - a sign of life!)

71
Q

What’s the formula for the energy of a photon?

A

E = hc
—
y(upside down)

72
Q

What does the E stand for in the energy of a photon formula (+unit)?

A

Energy (J)

73
Q

What does the h stand for in the energy of a photon formula?

A

The Planck constant

74
Q

What does the c stand for in the energy of a photon formula?

A

Speed of light in vacuo (on data booklet)

75
Q

What does the upside down y stand for in the energy of a photon formula (+units)?

A

Wavelength (m)

76
Q

Where does the Earth’s intensity of radiation peak? What does this mean?

A

Infrared- we can’t see at night, only with infrared glasses

77
Q

Which law states that the wavelength of peak emission from a black body is inversely proportional to the absolute temperature of the body?

A

Wien’s displacement law

78
Q

Which law shows us the total electromagnetic energy emitted per unit time by a black body?

A

Stefan’s law

79
Q

Which law tells us that less energy strikes each square metre of a surface per second as the distance from a light source increases?

A

The inverse square law

80
Q

What do we need to ensure when drawing a black body curve?

A

-Go through the origin (0)
-Don’t hit the x axis
-Show clearly where it peaks at (label it)
-Sharply up, gently down

+careful when converting between m and nm for wavelength!

81
Q

Which has the most dense atmosphere? The star’s surface or its atmosphere?

A

Surface

82
Q

What colour is a hotter star and why?

A

Blue as it peaks in ultra violet

83
Q

What colour is a colder star and why?

A

Red as it peaks in infared

84
Q

How many metres are in a nano metre?

A

1x10-9

85
Q

What happens to the area when you double the distance (inverse square law)?

A

x4

86
Q

What do you look at on the electromagnetic spectrum to figure out where a wavelength lies?

A

Wavelength

87
Q

Radio wave wavelength

A

10^3

88
Q

Microwave wavelength

A

10^-2

89
Q

infrared wavelength

A

10^-5

90
Q

Visible wavelength

A

.5x10^-6

91
Q

ultra violet wavelength

A

10^-8

92
Q

X-rays wavelength

A

10^-10

93
Q

Gamma wavelength

A

10^-12

94
Q

What shows us the total energy of a black body?

A

Area under the curve

95
Q

Explain the formation of dark bonds on the line absorption spectrum

A

-Continuous spectrum from the core of the star passes through its cooler atmosphere
-Certain photons will be equal to the energy level gaps in the atoms of the atmosphere
-These photons are absorbed by the electrons in the lower states
-Excited electrons
-Fall back down
-Release identical photon - not necessarily in the original direction
-Intensity (brightness) of colours is reduced

96
Q

Gamma rays characteristic temperature

A

More than 10^8 k

97
Q

X-rays characteristic temperature

A

10^6 - 10^8 k

98
Q

Ultra violet rays characteristic temperature

A

10^4-10^6 k

99
Q

Visible rays characteristic temperature

A

10^3-10^4 k

100
Q

Infrared rays characteristic temperature

A

10-10^3 k

101
Q

Radio waves characteristic temperature

A

Less than 10k

102
Q

What is R in the intensity formula?

A

Distance from the star (m)

103
Q

Why doesn’t a black body curve ever hit the x axis?

A

It emits at all wavelengths- its a black body

104
Q

What is area measured in?

A

Metres square

105
Q

Which type of radiation has subunits for telescopes and what are they?

A

Infrared -
Near, mid, far

106
Q

What’s wrong with using visible light as a telescope?

A

It doesn’t penetrate through dust clouds

107
Q

Name the process involving photons going up

A

Absorption

108
Q

Name the process involving photons going down

A

Emittion

109
Q

What’s the key thing that multi wavelength astronomy does?

A

Provides extra information - not limited to visible light

110
Q

What equations do we use to calculate the energy of a photon when given wavelength vs frequency?

A

Frequency
E=hf

Wavelength
E=hc
—
upside down y

111
Q

If you have to choose a region of the electromagnetic spectrum which the wavelength of peak emission lies, what do you choose from?

A

Infared, visible, ultra violet

112
Q

How do we explain a colour of a star, deducing it from the spectrum?

A

The (colour) end of the visible spectrum is nearer the peak, so it’s intensity is higher than the (opposite colour) end

113
Q

What would be the observed feature on a spectrum of a star to show absorption/emission?

A

Absorption - dark lines at that wavelength
Emission - coloured lines at that wavelength

114
Q

How do we explain why a star is a particular colour?

A

Peaks at (wavelength), so higher intensity of light at the (colour) end of the spectrum

115
Q

When is a black body graph’s gradient at zero (apart from at the extremes)?

A

At the peak

116
Q

What are continuous line spectra?

A

All visible wavelengths of light are present

117
Q

What are continuous line spectra produced by?

A

The atoms of heated metals

118
Q

How do you convert from Joulres to eV?

A

Divide by 1.60x10-19 (e on data sheet)

119
Q

When doing ratio questions with powers emitted by stars, what is it important to remember?

A

Cross cancel where possible
Do not cross-cancel indices as they’re part of the numbers that we DO have!

120
Q

If we’re drawing 2 black body curves on the same graph, what are three things we need to remember?

A
  1. Neither will hit 0
  2. They do not cross over each other
  3. For the cooler body, the entire curve is lower
121
Q

What can be seen at radio e-m wavelengths (multi-wavelength astronomy)?

A

Pulsars
Cool stars

122
Q

What can be seen at micro e-m wavelengths (multi-wavelength astronomy)?

A

Cosmic background radiation

123
Q

What can be seen at infared e-m wavelengths (multi-wavelength astronomy)?

A

Star formation (can see through dust)

124
Q

What can be seen at visible e-m wavelengths (multi-wavelength astronomy)?

A

Planets
Nebulae

125
Q

What can be seen at UV e-m wavelengths (multi-wavelength astronomy)?

A

Stars
Supernovae

126
Q

What can be seen at X-ray e-m wavelengths (multi-wavelength astronomy)?

A

Black holes and quasars

127
Q

What can be seen at gamma e-m wavelengths (multi-wavelength astronomy)?

A

Black holes and quasars

128
Q

Within which region of the e-m spectrum can black holes and quasars be seen?

A

X-ray and gamma

129
Q

Within which region of the e-m spectrum can stars and supernovae be seen?

A

UV

130
Q

Within which region of the e-m spectrum can planets and nebulae be seen?

A

Visibe

131
Q

Within which region of the e-m spectrum can star formation be seen?

A

Infared

132
Q

Within which region of the e-m spectrum can cosmic background radiation be seen?

A

Micro

133
Q

Within which region of the e-m spectrum can pulsars and cool stars be seen?

A

Radio

134
Q

Which part of the e-m spectrum can reveal star formation through dust?

A

Infared

135
Q

Hottest and highest energy end of the e-m spectrum

A

Gamma

136
Q

Coolest and lowest energy end of the e-m spectrum

A

Radio

137
Q

How do we calculate A in Stefan’s law?

A

4 x pi x radius^2

138
Q

What does a higher black body curve than another mean?

A

Higher temperature
Higher intensity (= higher brightness)

139
Q

Describe the main features of the spectrum of a star and sate where in the star they arise?

A

Continuous spectrum due to radiation of all wavelengths emitted from the surface of the star
Line absorption spectrum due to passage of radiation through atmosphere of star

140
Q

What should always be include in a multiwavelength astronomy question?

A

Link between wavelength and temperature

141
Q

What do we explain when explaining why a star would look “bluer”?

A

Greater spectral intensity at the blue end

142
Q

What do we need to remember to do if rearranging P = AoT^4 to work out a radius?

A

Multiply out the 4 and the pi first

143
Q

What does multi wavelength astronomy give us?

A

Extra information

144
Q

Why is the infrared part of the spectrum used to observe stellar formation?

A

Has a longer wavelength than the size of the dust particles = is not scattered by them
Penetrates the dust clouds in which the stars are being formed

145
Q

How can absorbing elements be identified from an absorption spectrum?

A

From the wavelength of lines

A level Physics (29 decks)

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