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# 6PH05 Physics Unit 5: From Creation To Collapse, June 20 watch

1. (Original post by Tomupcraft)
Have you finished the syllabus? If so which unit would you say is harder, unit 4 or 5?
Before half term, we had only not finished some radioactivity stuff and Hubbles stuff, but i did self taught it over half term, now im finished and would say that once you understand oscillations (hardest part) unit 5 is easier than unit 4

how far have you got, how are you finding it?
2. (Original post by Zzzyax)
Before half term, we had only not finished some radioactivity stuff and Hubbles stuff, but i did self taught it over half term, now im finished and would say that once you understand oscillations (hardest part) unit 5 is easier than unit 4

how far have you got, how are you finding it?
We are about halfway through nuclear decay with just astrophysics left to cover. Finding it a lot better and a lot more interesting than unit 4 as I hate electricity and fields but particle physics was great
3. perhaps someone can help me, what is the energy when a proton is accelerated through a p.d of 1 V, is it 1eV? (same energy as an electron because charges are the same?
4. (Original post by Zzzyax)
perhaps someone can help me, what is the energy when a proton is accelerated through a p.d of 1 V, is it 1eV? (same energy as an electron because charges are the same?
Voltage is energy per unit charge (E=VQ) so yes I think it is 1eV.
5. My school makes us do both modules during the summer, so huge potential to completely balls up my Physics grade...

However it does mean that we learn all the content first and then revise everything, that way there's no break in the middle for January module revision.
6. v=H0d
H0=v/d

and, 1/H0 = age of the universe ,

some ideas, at big bang as t--->0s, H0 hubbles constant is very large h0---> infinity, and as universes ages H0 gets smaller and smaller,

here's where i am confused H0 is the rate of expansion, but isnt it a well know fact that the expansion rate is increasing, i am really confused!!!

the problem i having is that if since the expansion of the universe is at present accelerating, the value of the Hubble constant is presently increasing

the Hubble constant must be decreasing because the universe is getting older and 1/H0= age of universe

7. (Original post by Zzzyax)
v=H0d
H0=v/d

and, 1/H0 = age of the universe ,

some ideas, at big bang as t--->0s, H0 hubbles constant is very large h0---> infinity, and as universes ages H0 gets smaller and smaller,

here's where i am confused H0 is the rate of expansion, but isnt it a well know fact that the expansion rate is increasing, i am really confused!!!

the problem i having is that if since the expansion of the universe is at present accelerating, the value of the Hubble constant is presently increasing

the Hubble constant must be decreasing because the universe is getting older and 1/H0= age of universe

I think the formula only applies if the universe is expanding at a constant rate, which evidence currently suggests is very unlikely. So I don't think that formula applies.
8. (Original post by brittanna)
I think the formula only applies if the universe is expanding at a constant rate, which evidence currently suggests is very unlikely. So I don't think that formula applies.
Hi, i am confused and perhaps someone can help mehaha i am so confused i need someone with atleast a phd or doctorate in physics )

v/d=H0

v= velocity of distant galaxy
H0= hubbles constant
d=distance to galaxy

The problem i having is that if since the expansion of the universe is at present accelerating, the value of the Hubble constant is presently increasing, the Hubble constant must/has always been decreasing because the universe is getting older and 1/H0 = age of universe

can someone tell me whether the hubbles constant is increasing or decreasing, and why.
At the big bang is hubbles constant very small, or very large?

Is density proportional to the hubbles constant? or what is the link between them, i guess that at big bang density is very large, which means very large gravational forces, rate of expansion is therefore slow, then as the universe expands and spreads out, expansion gets faster(density smaller) H0 is therefore bigger as time goes on, this is another contradiction to the earlier piont about, 1/H0 = age,

Is the Hubbles constant the exact same as the rate of expansion?

If the rate of expansion was constant, then as time goes by galaxies move further away and from hubbles law are moving faster and faster, so the rate of expansion is not constant its getting faster? someone explain please, you can see how confused i am.

Any help is appreciated! Thank you!
9. v = H0D. velocity of galaxy directly proportional to distance of galaxy from earth. rate of expansion is the hubble constant. the farther a galaxy, the faster it is receding from Earth. 1 parsec = 3.26 light years. Hubble constant was 500 km/s/Mpc. am i right?
10. hubble constant (1/t) is always decreasing. when the 'universe is expanding'. anyone can explain why?
11. Can someone describe an experiment to demonstrate resonance, using an electronic oscillator
12. (Original post by liowwc)
hubble constant (1/t) is always decreasing. when the 'universe is expanding'. anyone can explain why?
Because time is always increasing therefore if Hubble constant = 1/t then if t is always increasing then 1/t becomes smaller hence Hubble constant decreases.
13. is it true that when a star has used up all of its hydrogen, (still fusing helium, and other heavier elements), it immediately moves of the main sequence, and become a red giant
14. hows everyones revision going?
15. (Original post by Zzzyax)
is it true that when a star has used up all of its hydrogen, (still fusing helium, and other heavier elements), it immediately moves of the main sequence, and become a red giant
As far as I'm aware, a star never truly stops fusing hydrogen, it undergoes a kind of exponential decrease. And then lots of other factors come into play for how and when it becomes a red giant. Basically, I don't think there is a simple answer, so we are only expected to know that as a star runs out of hydrogen to fuse it will undergo the transformation to red giant.
16. (Original post by Zzzyax)
hows everyones revision going?
Haven't started on Physics yet. There doesn't seem to be that much to revise in physics though, so I'm concentrating on Chemistry at the moment.
17. hey guys do we need to know anything about real gas/ internal energy for this syllabus?
18. (Original post by freakynerdlol)
hey guys do we need to know anything about real gas/ internal energy for this syllabus?
We only need to know that an ideal gas is a very good approximation for any real gas under normal (i.e. not extreme) circumstances.

And internal energy is the sum of internal kinetic energy and the potential energy contained in a molecule.
19. oh btw is 'observed brightness' the same as radiation flux (F) ?
20. (Original post by freakynerdlol)
oh btw is 'observed brightness' the same as radiation flux (F) ?
Yes, I believe so.

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