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# OCR 21st century P7, unofficial mark scheme

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1. Labelling the parallax diagram (4 marks)
Earth
sun
Distant star / closer star)
Fixed background of (distant) stars

Label the parallax angle P (1 mark)

Work out the angle of parallax (3 marks)1/0.71 = 1.4 parsecs

The advantages of an international association (2 marks)
Can pull together different expertise
Can pull together money so not using money from government that could be used elsewhere such as in defence.

Who may have asked for the telescope to be built other than the IA (1mark)
The government? (not sure) perhaps the European Space Agency?

-No distortion/refraction from atmosphere
-atmosphere has an absorbing effect
-All EM radiation can be used and observed
-No light pollution
-No atmosphere in space
-Clearer images
-Can be costly to produce
-Hard to maintain

Why do light rays change direction when going through a lens? (3 marks)Different density/ boundary of glass and air
Causes light ray to change speed and wavelength
Causes a change in direction when they hit at an angle

Converging lens/light ray diagram (3 marks)
middle ray goes straight through
The other one converges after it goes through the middle of the lens

Which lens is the most powerful (1 mark)
W

Which lens would be the best eyepiece (2 marks)
W, shortest focal length so most powerful so bigger magnification

Which lens would be best for detecting light from a faint source (3 marks)The one with the biggest diameter -- Z as it had a diameter of 10cm
Larger aperture
Can detect and collect more light and radiation
Less diffraction
So clearer image produced

Is June correct in saying that W and Y would be most magnifying (4 marks)Yes she is correct in one way as you needs the shortest focal length for the eyepiece and the longest focal length for the objective to get the largest magnification according to the formula (quote it)
However the magnification was not 300 it was 30 so she's wrong in that way.

Find the approximate distance across the gas nebulae (2 marks)
Can't remember but I took the mean of all 8 stars

Find the approximate depth of the gas nebulae (2 marks)
1000 light years (that's what I got because 1040 light years -40)

Cepheid variables and Hubble's constant (6 marks) (horrible question!!!)
- Longer pulse period has a higher luminosity
-stars which are cepheids that have the same apparent or observed brightness but different luminosity (pulse period) can be compared to find distance
-using redshift we can find recession velocity
-using these cepheid's we can find distanceuse formula to find hubble's constant

Describe fusion in the sun (3 marks)
fusion between hydrogen nucleui to make hydrogen through the proton-proton chain to produce energy.
Positrons are used to conserve energy
Hydrogen fuses under high pressures and temperatures to make helium
Only happens if the nuclei are close together

Calculate the mass using E=mc^2 (2 marks)
4.8 x 10 -- not sure
not sure

Explain how the energy is transferred through the sun (4 marks)
Energy created in core
Convection zone- convection currents

Sidereal days, solar days and the moon (6 marks)
Sidereal day - 23 hours 56 minutes as Earth turns 360 degrees
Solar day- 24 hours as more than 360 degrees turned
Moon- 25 hours as the moon orbits in the same direction that the Earth orbits the sun (I think, not too sure what else I wrote for this question)

I don't want to put most of my answers in because they are most likely wrong! SO feel free to suggest your own answers
2. (Original post by Lsford)
Labelling the parallax diagram (4 marks)
Earth
sun
Distant star (I put closer star)
Fixed background of (distant) stars

Label the parallax angle P (1 mark)

Work out the angle of parallax (3 marks)
1/0.71 = 1.4 parsecs

The advantages of an international association (2 marks)
can pull together different expertise
Can pull together money so not using money from government that could be used elsewhere such as in defence.

Who may have asked for the telescope to be built other than the IA (1 mark)
The government? (not sure) perhaps the European Space Agency?

-No distortion/refraction from atmosphere
-atmosphere has an absorbing effect
-All EM radiation can be used and observed
-No light pollution
-No atmosphere in space
-Clearer images
-Can be costly to produce
-Hard to maintain

Why do light rays change direction when going through a lens? (3 marks)
Different density/ boundary of glass and air
Causes light ray to change speed and wavelength
Causes a change in direction when they hit at an angle

Converging lens/light ray diagram (3 marks)
middle ray goes straight through and the other one converges after it goes through the middle of the lens
Which lens is the most powerful (1 mark)
W?

Which lens would be the best eyepiece (2 marks)
W, shortest focal length so most powerful so bigger magnification

Which lens would be best for detecting light from a faint source (3 marks)
The one with the biggest diameter -- Z as it had a diameter of 10cm
Larger aperture
Can detect and collect more light and radiation
Less diffraction
So clearer image produced

Is June correct in saying that W and Y would be most magnifying (4 marks)
Yes she is correct in one way as you needs the shortest focal length for the eyepiece and the longest focal length for the objective to get the largest magnification according to the formula (quote it) however the magnification was not 300 it was 30 so she's wrong in that way.

Find the approximate distance across the gas nebulae (2 marks)
can't remember but I took the mean of all 8 stars
Find the approximate depth of the gas nebulae (2 marks)
1000 light years (that's what I got because 1040 light years -40)

Cepheid variables and Hubble's constant (6 marks)
(horrible question!!!)
longer pulse period has a higher luminosity
stars which are cepheids that have the same apparent or observed brightness but different luminosity (pulse period) can be compared to find distance
using redshift we can find recession velocity and using these cepheid's we can find distance
use formula to find hubble's constant

Describe fusion in the sun (3 marks)
fusion between hydrogen nucleui to make hydrogen through the proton-proton chain (I wrote it out heree) to produce energy. Positrons are used to conserve energy
Calculate the mass using E=mc^2 (2 marks)
4.8 x 10 -- not sure
not sure
Explain how the energy is transferred through the sun (4 marks)
Energy created in core
Convection zone- convection currents

Sidereal days, solar days and the moon (6 marks)
Sidereal day - 23 hours 56 minutes as Earth turns 360 degrees
Solar day- 24 hours as more than 360 degrees turned
Moon- 25 hours as the moon orbits in the same direction that the Earth orbits the sun (I think, not too sure what else I wrote for this question)

I don't want to put most of my answers in because they are most likely wrong! SO feel free to suggest your own answers
These are my improvements
These are my improvements
Thanks!!!!
4. The first E=mc^2 i got something followed by 10^-29? Im sure that is messed up in some way but it asked to calulate the mass so i did m = E/c^2 and it gave me that. Luminosity calculation below i did energy a second and the luminosity, then multiplied together. The numbers for those calculations were horrible, but the rest of the paper i did okay i think (the second 6 marker up for debate though)
5. (Original post by Lsford)
Labelling the parallax diagram (4 marks)
Earth
sun
Distant star / closer star)
Fixed background of (distant) stars

Label the parallax angle P (1 mark)

Work out the angle of parallax (3 marks)1/0.71 = 1.4 parsecs

The advantages of an international association (2 marks)
Can pull together different expertise
Can pull together money so not using money from government that could be used elsewhere such as in defence.

Who may have asked for the telescope to be built other than the IA (1mark)
The government? (not sure) perhaps the European Space Agency?

-No distortion/refraction from atmosphere
-atmosphere has an absorbing effect
-All EM radiation can be used and observed
-No light pollution
-No atmosphere in space
-Clearer images
-Can be costly to produce
-Hard to maintain

Why do light rays change direction when going through a lens? (3 marks)Different density/ boundary of glass and air
Causes light ray to change speed and wavelength
Causes a change in direction when they hit at an angle

Converging lens/light ray diagram (3 marks)
middle ray goes straight through
The other one converges after it goes through the middle of the lens

Which lens is the most powerful (1 mark)
W

Which lens would be the best eyepiece (2 marks)
W, shortest focal length so most powerful so bigger magnification

Which lens would be best for detecting light from a faint source (3 marks)The one with the biggest diameter -- Z as it had a diameter of 10cm
Larger aperture
Can detect and collect more light and radiation
Less diffraction
So clearer image produced

Is June correct in saying that W and Y would be most magnifying (4 marks)Yes she is correct in one way as you needs the shortest focal length for the eyepiece and the longest focal length for the objective to get the largest magnification according to the formula (quote it)
However the magnification was not 300 it was 30 so she's wrong in that way.

Find the approximate distance across the gas nebulae (2 marks)
Can't remember but I took the mean of all 8 stars

Find the approximate depth of the gas nebulae (2 marks)
1000 light years (that's what I got because 1040 light years -40)

Cepheid variables and Hubble's constant (6 marks) (horrible question!!!)
- Longer pulse period has a higher luminosity
-stars which are cepheids that have the same apparent or observed brightness but different luminosity (pulse period) can be compared to find distance
-using redshift we can find recession velocity
-using these cepheid's we can find distanceuse formula to find hubble's constant

Describe fusion in the sun (3 marks)
fusion between hydrogen nucleui to make hydrogen through the proton-proton chain to produce energy.
Positrons are used to conserve energy
Hydrogen fuses under high pressures and temperatures to make helium
Only happens if the nuclei are close together

Calculate the mass using E=mc^2 (2 marks)
4.8 x 10 -- not sure
not sure

Explain how the energy is transferred through the sun (4 marks)
Energy created in core
Convection zone- convection currents

Sidereal days, solar days and the moon (6 marks)
Sidereal day - 23 hours 56 minutes as Earth turns 360 degrees
Solar day- 24 hours as more than 360 degrees turned
Moon- 25 hours as the moon orbits in the same direction that the Earth orbits the sun (I think, not too sure what else I wrote for this question)

I don't want to put most of my answers in because they are most likely wrong! SO feel free to suggest your own answers
gas nebluae questions are weong I believe
They said some of the stars were formed from same gas cloud

keyword some:
these stars were 160, 165, 175, and 180 light years away
they asked u to find approximatiom center of gas nebulae
its 170 because mean of all 4 is 170. Mean is best estimate and it is in bwtween range

secons part asked u to find depth
simple 180-160, depth was 20 light years
a gas cloud wont span 1000 light years and it is improbable to say star at distznce 40 light years was made by same gas cloud as star of sistance 1000 lightyears.
6. (Original post by LokiiR)
gas nebluae questions are weong I believe
They said some of the stars were formed from same gas cloud

keyword some:
these stars were 160, 165, 175, and 180 light years away
they asked u to find approximatiom center of gas nebulae
its 170 because mean of all 4 is 170. Mean is best estimate and it is in bwtween range

secons part asked u to find depth
simple 180-160, depth was 20 light years
a gas cloud wont span 1000 light years and it is improbable to say star at distznce 40 light years was made by same gas cloud as star of sistance 1000 lightyears.
I swear that they asked for the distance across the gas nebulae tho?but thanks for your answers!
7. (Original post by Lsford)
I swear that they asked for the distance across the gas nebulae tho?but thanks for your answers!
They asked for the distance to the centre of the nebulae, so when i got 170 I divided it by 2 to get the distance to the centre. Not sure if its right.
8. I got around 50 in this, happy
9. (Original post by LokiiR)
gas nebluae questions are weong I believe
They said some of the stars were formed from same gas cloud

keyword some:
these stars were 160, 165, 175, and 180 light years away
they asked u to find approximatiom center of gas nebulae
its 170 because mean of all 4 is 170. Mean is best estimate and it is in bwtween range

secons part asked u to find depth
simple 180-160, depth was 20 light years
a gas cloud wont span 1000 light years and it is improbable to say star at distznce 40 light years was made by same gas cloud as star of sistance 1000 lightyears.
For the first bit I eliminated B, F and H as outliers and got an answer of 200, would this be right or should I have eliminated the 320 one as well?
Because of this I got 160 as the depth, is that too big?
10. (Original post by Lsford)
I swear that they asked for the distance across the gas nebulae tho?but thanks for your answers!
first one was cwnter of the gas nebulae second was its depth or thickness

(Original post by NiamhM1801)
For the first bit I eliminated B, F and H as outliers and got an answer of 200, would this be right or should I have eliminated the 320 one as well?
Because of this I got 160 as the depth, is that too big?
im not sure of the exact answer but I think so because i assumed the others were too distant to be part of the same gas cloud, only took the four values which were 160 165 175 and 180 and yeah 160 lightyears seems too big for thickness, you might be right though and i might be wrong 😂 that test was really short and I did good in other parts so I'm glaad

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Updated: June 25, 2016
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