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Physics > P3 - Astrophysics > Flashcards

P3 - Astrophysics Flashcards

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1
Q

what are converging lenses?
what is the principal axis?
what is the lens axis?

A

convex lenses that cause rays of light to refract and bend towards each other.

the horizontal axis through the centre of the lens

the vertical axis

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2
Q

what are the axial rays?

where do the axial rays converge too?

A

axial rays are rays that are parallel to the principle axis. They converge into the principle focus

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3
Q

What are non axial rays?

where do these converge?

A

axial rays are rays that are not parallel to the principle axis.
Parallel non axial rays converge somewhere else on the focal plane

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4
Q

what is the focal plane?

A

the plane that is perpendicular to the principal axis that contains the principle focus

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5
Q

what is the focal length?

A

the perpendicular distance between the lens axis and the focal plane

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6
Q

What is the objective lens?

A

the objective lens converges the rays from the object to form a real image inside the telescope.

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7
Q

what is the eye lens?

A

acts as a magnifying glass on this real image to form a magnified virtual image which the observer can then view

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8
Q

when viewed in an astromical refracting lens where is the real image formed?

A

on the focal plane of the objective lens

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9
Q

what is a telescope in normal adjustment?

why do we have it like this?

A

is set up so the principal focus of the objective lens is in the same position as the principal focus of the eye lens.
This means the rays form the real image come out of the eye lens parallel and the final magnified image appears to be at infinity.

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10
Q

What is the length of the telescope?

A

Focal length of objective lens (f0) added to the focal length of the eye lens (fe)
f0 + fe = total length

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11
Q

draw the double converging lens in normal adjustment

A

good luck

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12
Q

what does M stand for?

what is the difference between the image by the unaided eye and image eye?

A

angular magnification

baso how much bigger the image eye is so how much it is magnified by

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13
Q

what does f0 and fe mean?

A

focal length of the objective lens

focal length of the eye lens

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14
Q

What focal length from what lens is bigger out of objective and eye?

A

objective focal length is much much bigger then eye lens focal length

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15
Q

What does it mean by the luminosity of a star?

what is luminosity measured in?

A

luminosity is the power output of a star

Watts

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16
Q

what is the intensity/brightness of an object? in relation to planets

A

the intensity of an object that we observe is the power received from it per unit area at earth, aka the effective brightness of an object

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17
Q

what is apparent magnitude?

A

the measurement of the intensity of the star (the brightness as we look at it from earth)

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18
Q

What is the scale of the dim to bright star?

A

a logarithmic scale

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19
Q

What is the absolute magnitude?

A

The absolute magnitude of an object, M, is only on the power output of an object. It does not depend on its distance from earth

20
Q

In the absolute magnitude equation what does m and M stand for?
what is the base of the log?
what is d and what unit is it measured in?

A

m is apparent
M is absolute
logbase 10
distance and parsec

21
Q

What is a standard candle?

A

a standard candle are objects that have a known absoutle magnitude

22
Q

when working out the distance in the absolute magnitude equation how do you rearrange for d?

A

re arrange and raise everything to the power of 10 to get rid of the log

23
Q

What is the doppler effect?

A

The doppler effect is when an object moves that emits sound, the waves bunch up in front of the object and spread out behind the object.

24
Q

What is red shift?

A

The doppler effect happens with all waves including electromagnetic radiation.

When a light source moves away from us the wavelength of the light reaching us becomes longer and the frequency becomes lower, shifting the em wave towards the red end of the spectrum so is called red shift

25
Q

what is blue shift?

A

when a light source moves towards us the EM waves emitted becomes higher frequency lower wavelength so moves towards the blue side of the spectrum so is blue shift

26
Q

What does the amount of blue/ red shift depend on?

A

The higher the velocity the more shift we experience

27
Q

What does Z stand for?
v?
C?

A

Z stands for red shift
v stands for recessional velocity of the source in line with the observer
c is speed of EM radiation wave in vacuum

28
Q

what does v &laquo_space;c mean?

A

This only works for velocity’s much less then c

29
Q

when using blue/red shift equation, what does it mean if v < 0?
when v > 0?

A

v > 0 means it is positive so it is red shift

v < 0 means it is negative so blue shift

30
Q

what does f, delta f, landa, delta landa mean? what they used for?

A

f = frequency
delta f = the change in frequency
landa means the wavelength
delta landa means the change in wavelength

31
Q

what is cosmological red shift?

A

cosmological red shift is not red shift from a moving source but how space itself is expanding and the light is going with it, works the same with the equation as long as v is much less than c

32
Q

What does homogeneous mean?
what does isotropic mean?
(the cosmological principle)

A

homogeneous means every part of the universe is the same as every other part

isotropic means everything looks the same in every direction so it doesn’t have a centre

33
Q

In the hubbles law equation what does v, H, d stand for? unit?

A 
V = Reccisonal velocity in kms 
H = the hubble constant in kms Mpc 
d = Distance in Mpc
34
Q

What is the big bang theory?

A

The universe started off very hot and very dense (perhaps as an infinitely hot infinitely dense point) and has been expanding ever since

35
Q

Why is red shift evidence for the big bang theroy?

A

The spectra from all galaxies expect ones very close to us show red shift, this shows that they are all moving apart. universe is moving away from us uniformly

36
Q

what is the equation for the age of the universe?

what units for d and v?

A

T = 1/h which is equal to d/v
Parsec for d
kms for v

37
Q

What is cosmic microwave background radiation?

What does it show?

A

the big bang model predicts that loads of electromagnetic radiation was produced in the very early universe, which should be observable today.

shows doppler effect and the WMAP image shows homogenous and isotropic with small variation

38
Q

Why is there a relative abundance of H and He?

A

The early universe had been very hot so fusion could happen, cant now it cooled down

39
Q

what is a parsec?

A

The Distance at which 1 AU subtends an angle of is 1/3600degrees (1 arcsecond)

40
Q

What is the resovling power of a telescope?

What is it dependant on?

A

is the measure of how much detail you can see

It is depenadant on the minimum angular resolution, which is the smallest angle at which the instrument can distinguish two points.

41
Q

How do you get a better resovling power?

A

The smaller the minimum angular resolution, the better the resovling power of the telescope.

42
Q

what is theatre?
landa?
D?

A

thearte = minimum angular resolution in radians

landa is wavlength in Metres

Diameter in metres

43
Q

When can 2 light sources be distinguished?

A

when the centre of the airy disc from one source is at least as far away as the first minimum of the other source

44
Q

What is chronic abbreviation?

A

Glass refracts different colours of light by different amounts as they have differebt wavelngths and so the image for each colour is in a slightly different position causing a blur.

45
Q

other than colour what else causes an unclear image in a refracting lens?
What problems do we have with big lenses?

A

Any bubbles or inpurities absorb some of the light which means that very faint objects arent seen.

The objective lens needs to have a very long focal length so the telescope is very long so big buildings need to house them.
Heavy so can omly be carried by there sides and there edges can be disorted, diffuiclt and expensive to build.

46
Q

what is the lens equation?

A 
1/f = 1/u = 1/v  
U = the distance between the objective and the lens axis 
F =  focal length
V = the distance between image and the lens axis is known as v.

Physics (14 decks)

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