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A-Level Physics > Astrophysics > Flashcards

Astrophysics Flashcards

1
Q

what are the 2 types of optical telescope and what lens do they use

A

refracting and reflecting telescopes. they both use convex lenses

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2
Q

what’s another name for a convex lens

A

a converging lens

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3
Q

what are the 5 key features on a ray diagram

A

principle axis
lens axis
principal focus
axial rays
focal length

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4
Q

what is an axial ray

A

a ray that is parallel to the principal axis

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5
Q

what are the 4 key steps when drawing ray diagrams with 1 lens

A

-draw an axial ray from the top of the object, and is refracted and goes through the focus point
- draw a ray from the top of the object straight through the centre of the lens axis
-draw a ray through the focal point on the left side and parallel from the lens axis
-draw the object

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6
Q

what is the scenario for an object more than 2f away

A

image position-between f-2f
orientation- inverted
magnified/diminished-diminished
application- camera

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7
Q

what is the scenario for an object at 2f

A

image position- at 2f
orientation- inverted
magnified/diminished- same size
application- inverter

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8
Q

what is the scenario for an object between f-2f

A

image position- beyond 2f
orientation-inverted
magnified/diminished- magnified
application-projector

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9
Q

what is the scenario for an object closer than f

A

image position- same side as object
orientation-upright
magnified/diminished-magnified
application-magnifying glass

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10
Q

what is the difference between real and virtual images

A

real images of inverted and virtual ones are not.

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11
Q

in the lens equation, what does it mean when v is negative

A

its a virtual image. if its positive-its real

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12
Q

how do you calculate the length of the telescope

A

fo+fe

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13
Q

how do you calculate magnification

A

M=fo/fe

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14
Q

how do refracting telescopes work

A

they use 2 lenses to form a magnified image. objective (larger/closer to image) and eyepiece (smaller/ further from image)

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15
Q

how do you calculate to get the greatest magnification

A

having the objective focal length a high as possible

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16
Q

how would you get a clear image

A

make sure the 2 focal lengths meet at the same point

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17
Q

what are the steps for drawing a ray diagram with 2 lenses

A

-Draw a non-axial ray through the centre of the
objective lens axis to the eyepiece lens axis
-Draw two parallel rays either side
-These should meet at the focus and then stop on the
eye lens axis
-Draw a construction line that starts from where the rays cross over and passes through the centre of the eyepiece lens
-The three rays emerge parallel to this line

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18
Q

how do you calculate magnification with angles

A

M= angle subtended by image/
angle subtended by object

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19
Q

how do reflecting telescopes work

A

they use a parabolic mirror to reflect the rays instead of lenses.
a secondary mirror is placed before the focal point which reflects the rays through the hole in the mirror, emerging parallel
this is know as the cassegrain telescope

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20
Q

what is a CCD

A

CCD-charged coupled device
used to take digital photos eg. camera

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21
Q

what are the physical characteristics of a CCD

A

consists of a series of silicon picture elements (pixels), which are very small (not pixels on a screen)
beneath each one is a potential well, which traps electrons. and above is a filter that only allows certain colour photons through

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22
Q

how do CCDs work

A
  1. filter only allows certain wavelengths of light to hit the pixels
  2. photons cause electrons to be released into the potential wells. electrons released is proportional to intensity of the photons
  3. the charge is then collected in the wells. and the amount of charge and the filter tells the computer what colour and brightness is displayed
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23
Q

what is quantum efficiency equation

A

number of photons detected/ X100
number of photons incident

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24
Q

what are the advantages of CCDs (quantum efficiency)

A

quantum efficiency=
CCDs- 80%
photographic film- 4%
naked eye- 1%

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25
what are the advantages of CCDs
exposing film to too much light it gets saturated, which a CCD doesn't CCDs can detect a larger range of light (invisible spectrum) the minimum resolvable distance is 10microm compared to 100microm for naked eye (CCDs see finer detail) CCDs have longer exposure to capture fainter images
26
what is chromatic aberration
light is reflecting different amounts through a lens due to its wavelength. blue light forms to close to the lens whereas red from to far creating a bleeding affect
27
which telescope has a bigger problem with chromatic aberration
refracting due to its larger lens
28
what are the 3 other problems with refracting telescopes
impurities-bubbles and impurities will scatter the light affecting faint objects lens distortion- lenses are very heavy and can only be supported at the edge creating distortion length of telescope- for a better magnification the focal length needs to be much larger so large expensive buildings are needed to house them
29
what are the 4 advantages of reflecting telescopes
cost-large mirrors of good quality or cheaper then lenses support structure- mirrors can be supported from the back decreasing change of distortion collecting power-the larger the telescope the more light collected and the dimmer the object can be seen better resolving power-
30
what are the 2 disadvantages of a reflecting telescope
spherical aberration- happens when the mirror isn't a perfect parabola. when the outer rays form too close and the inner rays form to far, causing blurry images. second mirror-a secondary mirror can also block light and decrease image clarity
31
what happens to light when diffracted through a circular opening
creates a circular diffraction pattern consisting over light (maxima) rings and dark (minima) rings and the central maxima called the airy disc
32
what is the Raleigh Criterion
how to distinguish of stars are resolved or not. two light sources can be distinguished if the centre of one of the airy discs is at least one minima away from the other source
33
how can you calculate resolving power
angle=wavelength/d a smaller angle means a more more powerful telescope. the smaller the wavelength and larger the diameter the better.
34
what other unit may be used when measuring the angle subtended by an object in space
arc seconds 1 arc second= 1/3600 of a degree
35
why are non optical telescopes built
because of so much radiation in the universe eg. microwave from cosmic background - x-ray from blackholes
36
what is the structure like in non optical telescopes
nearly all use a parabolic dish to focus EM radiation to a point. visible/uv/ infrared will use a CCD at this point but radio will use amplifies to boost weak signals and a tuner to focus on specific frequencies x-ray use grazing mirrors so they are not absorbed making the telescopes very longer. a geiger counter/CCD is used a a detector
37
what is perfection in a non-optical telescope
an imperfection cannot be greater than 1/20th of the wavelength. (bumps and holes) because UV is the shortest EM wave it has to be the most perfect and radio is this least making this better for radio telescope
38
what is resolving power in a non-optical telescope
a higher resolving power means a smaller minimum angle when resolving 2 stars. directly proportion to wavelength so shorter wavelengths and bigger telescopes give better resolving power - radio isn't good for this
39
what is collection power in a non-optical telescope
linked to the area- the more area, the more photons can hit it. allowing us to see dimmer stars (less of there photons reach us) radio is the best for this as they are the cheapest to make collection power is proportional to d^2
40
how does location affect non-optical telescopes
the atmosphere blocks some wavelengths so UV/infrared/x-ray are put in space. radio and visible light telescopes can be put on ground (cheaper)
41
what is a disadvantage of only infrared
they will heat up and need cooling down. coolant will only last a few years
42
what is the parallax method
comparing the view of stars form opposite sides of earth, to get a more accurate placement of them in the sky. distant stars won't appear to move but closer ones will appear in different positions
43
what is an astronomical unit
the centre of earth to the centre of the sun (r)
44
how to get the distance from earth to the star
using r (1Au) and the angle of parallax, using trig can calculate the distance. you can also use small angle approximations
45
what is a parsec
an object is exactly one parsec away when 1Au subtends an angle of 1 arcsecond
46
what is a light year
c=3.00 x10^8 the distance light travels in one year is 1 light year
47
What two things affect a stars brightness
-its power output -how far away it is from us
48
What is power output/luminosity
The total amount of energy emitted (in EM radiation form) It’s measured in watts
49
What is the intensity equation
Intensity= power/area
50
what is apparent magnitude
The brightness of a star when viewed from earth
51
What is the hipparcos scale
An apparent magnitude scale going from 1-6 1 being brightest and 6 being dimmest A star with an apparent magnitude of 1 is 100 times brighter than a star- apparent magnitude 6 It’s a logarithmic scale
52
What is the modern hipparcos scale
It keeps the logarithmic 2.51 increments but extends the scale, brighter objects being negative and dimmer objects exceeding 6
53
What is the brightness ratio equation
I2/I1=2.51^m1-m2
54
What is absolute magnitude
How bright a star is when it’s put 10 parsecs away. This is fairer as it has nothing to do with earth
55
What apparent and absolute magnitude does our sun have
Apparent- -27 Absolute- 4.8
56
What is a type 1a supernova
Also known as standard candles - unique as when they explode all have the same peak absolute magnitude (-19.3) -because they are so bright we can see them from very far away, allowing us to measure the distance to distant galaxies
57
Draw a type 1a supernova light curve
(Check on century) Scale: Y-axis = 0–20 (Absolute magnitude) X-axis= 0-300 (Time in days)
58
59
What is a black body
An object that absorbs all types of EM radiation form
60
What is black body radiation
The radiation stars emit, they emit all types of EM radiation but not in equal quantities. Giving it the collective name black body radiation
61
What is a black body radiation curve
It shows the amount of radiation being produced by each wavelength (Look on century)
62
How to temperature link into a black body radiation curve
Hotter stars produce more radiation and peak at a shorter wavelength so they appear more blue whereas cooler stars appear more red and have a lower intensity
63
What do extremely hot objects look like on black body curves
Extremely hot objects (events horizon in black holes) can peak in the gamma. Therefore it will appear less bright if most of the radiation produces is invisible This emphases the use of non-optical telescopes
64
What are the 2 main things that affect the power output of a star
The temperature of the star The surface area of the star
65
What are the 7 spectral classes
O B A F G K M
66
What are the 7 classes based on
Surface temperature There absorption spectra
67
How are absorption spectra formed
Electrons in a gas are able to absorb very specific energies of photons, unique to that element. Because stars are black bodies they produce a continuous spectra. So the atmosphere around them absorb some of the photons produce creating the absorption spectra. (See which photons were blocked)
68
How are absorption spectra affected by temperature
The hotter the star the more energy each electron has, so they sit in higher energy levels. Therefore there are less photons that can be absorbed so there are less absorption lines.
69
What are hydrogen-balmer lines
The absorption lines created by electrons in hydrogen at level 2 only. There are no electrons in ground state as its too hot
70
How does temperature affect hydrogen- balmer lines
Hotter stars wont have very intense lines as most electrons are in n=3 Cooler stars wont have very intense lines as most electrons are in n=1 A class is where there most intense as the majority of electrons are in n=2, therefore most intense
71

A-Level Physics (14 decks)

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