P3 - Astrophysics

Question 1

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

Answer 1

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

Question 2

what are the axial rays?

where do the axial rays converge too?

Answer 2

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

Question 3

What are non axial rays?

where do these converge?

Answer 3

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

Question 4

what is the focal plane?

Answer 4

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

Question 5

what is the focal length?

Answer 5

the perpendicular distance between the lens axis and the focal plane

Question 6

What is the objective lens?

Answer 6

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

Question 7

what is the eye lens?

Answer 7

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

Question 8

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

Answer 8

on the focal plane of the objective lens

Question 9

what is a telescope in normal adjustment?

why do we have it like this?

Answer 9

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.

Question 10

What is the length of the telescope?

Answer 10

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

Question 11

draw the double converging lens in normal adjustment

Answer 11

good luck

Question 12

what does M stand for?

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

Answer 12

angular magnification

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

Question 13

what does f0 and fe mean?

Answer 13

focal length of the objective lens

focal length of the eye lens

Question 14

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

Answer 14

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

Question 15

What does it mean by the luminosity of a star?

what is luminosity measured in?

Answer 15

luminosity is the power output of a star

Watts

Question 16

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

Answer 16

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

Question 17

what is apparent magnitude?

Answer 17

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

Question 18

What is the scale of the dim to bright star?

Answer 18

a logarithmic scale

Question 19

What is the absolute magnitude?

Answer 19

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

Question 20

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?

Answer 20

m is apparent
M is absolute
logbase 10
distance and parsec

Question 21

What is a standard candle?

Answer 21

a standard candle are objects that have a known absoutle magnitude

Question 22

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

Answer 22

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

Question 23

What is the doppler effect?

Answer 23

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.

Question 24

What is red shift?

Answer 24

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

Question 25

what is blue shift?

Answer 25

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

Question 26

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

Answer 26

The higher the velocity the more shift we experience

Question 27

What does Z stand for? v? C?

Answer 27

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

Question 28

what does v << c mean?

Answer 28

This only works for velocity's much less then c

Question 29

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

Answer 29

v > 0 means it is positive so it is red shift | v < 0 means it is negative so blue shift

Question 30

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

Answer 30

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

Question 31

what is cosmological red shift?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

``` V = Reccisonal velocity in kms H = the hubble constant in kms Mpc d = Distance in Mpc ```

Question 34

What is the big bang theory?

Answer 34

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

Question 35

Why is red shift evidence for the big bang theroy?

Answer 35

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

Question 36

what is the equation for the age of the universe? | what units for d and v?

Answer 36

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

Question 37

What is cosmic microwave background radiation? | What does it show?

Answer 37

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

Question 38

Why is there a relative abundance of H and He?

Answer 38

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

Question 39

what is a parsec?

Answer 39

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

Question 40

What is the resovling power of a telescope? | What is it dependant on?

Answer 40

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.

Question 41

How do you get a better resovling power?

Answer 41

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

Question 42

what is theatre? landa? D?

Answer 42

thearte = minimum angular resolution in radians landa is wavlength in Metres Diameter in metres

Question 43

When can 2 light sources be distinguished?

Answer 43

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

Question 44

What is chronic abbreviation?

Answer 44

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.

Question 45

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

Answer 45

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.

Question 46

what is the lens equation?

Answer 46

``` 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. ```