PHYA5 ~ 20th June 2013 ~ A2 Physics

so theres two long answer questions in unit 5......

and I was starting to think that this was easier than unit 4

unit 4 is definitely better than this, only one 6 markers, and the grade boundaries nicer as well

Not that i'm going to get a good grade on this (screwed myself with a lack of time), but i think the depth of the content for unit 5 is easier to get to terms with than unit 4. Unit 4 was mental whereas unit 5 has more of an opportunity for blabbing and potentially getting away with it :smile:

. I.e i think, despite having 2 of them, the 6 markers are quite nice. Just do, and redo, all of the wordy questions as many times as possible and you are sure to pick up some marks on those....

Reply 901

Jack93o

15

astro related

why did the observation of the type 1a supernova led to the conclusion that the universe expansion was accelerating?

the mark scheme for this 6 marker in june 2010 isn't very clear :s-smilie:

Reply 902

Jack93o

15

Original post by kingm

Not that i'm going to get a good grade on this (screwed myself with a lack of time), but i think the depth of the content for unit 5 is easier to get to terms with than unit 4. Unit 4 was mental whereas unit 5 has more of an opportunity for blabbing and potentially getting away with it :smile:

. I.e i think, despite having 2 of them, the 6 markers are quite nice. Just do, and redo, all of the wordy questions as many times as possible and you are sure to pick up some marks on those....

tbh, my problem is mainly to do with time, I wouldn't mind the 6 markers too much if I had more time to properly organize my thoughts and put it into concise wording

unlike the maths/simple explaining concepts questions, you can't really blast through these 6 markers, they bog you down in the exam, at least thats what happens with me

Reply 903

JRP95

2

Original post by Jack93o

astro related

why did the observation of the type 1a supernova led to the conclusion that the universe expansion was accelerating?

the mark scheme for this 6 marker in june 2010 isn't very clear :s-smilie:

Type 1 supernova were found to have lower absolute magnitudes than expected from their light curves, indicating it is further away than expected if the universe was expanding at a constant rate.

Reply 904

Jack93o

15

Original post by JRP95

Type 1 supernova were found to have lower absolute magnitudes than expected from their light curves, indicating it is further away than expected if the universe was expanding at a constant rate.

don't you mean apparent magnitude?

and also, doesn't hubble's equation already suggest that the universe would expand at an accelerating rate?

a constant rate of expansion would be if the galaxies move away at constant velocity, but hubble's equation already shows than velocity would increase (so galaxies would accelerate) with increased distance moved, so I don't get why they didn't know the universe expansion was accelerating just from looking at hubble's equation

Reply 905

franko06

Can someone who does Astrophysics please explain CCDs to me in the simplest form? They're really confusing

Reply 906

Allahu Akbar

Original post by franko06

Can someone who does Astrophysics please explain CCDs to me in the simplest form? They're really confusing

Structure

•

CCDs are silicon chips divided in to pixels

•

Each pixel contains three electrodes lined up in adjacency

•

During exposure, centre electrode has potential of +10V and outer electrodes of +2V

How they work

•

During exposure (i.e. when the photo is being taken) there are photons incident on the CCD

•

When a photon is detected (occurs with 70% of all incident photons - called quantum efficiency) it liberates an electron in whichever pixel it hits

•

Due to its high potential as stated above, the electron collects on the centre electrode in the pixel

•

Process repeats millions/billions of times and once exposure time is completed, the charge on each central electrode (corresponds to no. of electrons liberated and therefore no. of photons incident) is read by altering the p.d of the electrodes (details aren't needed)

•

This charge is proportional to the intensity of the light/no. of photons incident on the particular pixel in the given time period of exposure

•

Hence, computer can build picture

Reply 907

ladynova

16

Original post by Jack93o

don't you mean apparent magnitude?

and also, doesn't hubble's equation already suggest that the universe would expand at an accelerating rate?

a constant rate of expansion would be if the galaxies move away at constant velocity, but hubble's equation already shows than velocity would increase (so galaxies would accelerate) with increased distance moved, so I don't get why they didn't know the universe expansion was accelerating just from looking at hubble's equation

it is because it is unknown whether hubbles constant was constant at the big bang and the start of the universe. Until they discovered dark matter they thought it was decelerating. When they looked at hubbles equation I think they believed it was still expanding but at a slower rate so deceleration.

(edited 10 years ago)

Reply 908

Xiomara

18

Original post by posthumus

A fairly silly question I suppose :tongue:

Any question where you have the values for 4 of those variables/constants!

Also rearranging it you can kind of see what it means :smile:

firstly you can see that pressure & volume are both proportional to temperature and also if you rearrange it you'd find that pressure and volume have an inverse relationship :smile:

Haha, this is what I meant:

Original post by kabutsu12

the Nkt is for when you have N molecules, nRt is for when you have n moles.

Does anyone reckon mole calculations will come up? Similar to those you get in chemistry?

Thank you!

Reply 909

JayJay95

Hey guys, in the book it says take 1u to be 931.3 Mev but on the formula sheet it says 931.5 Mev. Even highlights this on page 183 of nelson thornes examiners tips section.

Any thoughts?

Posted from TSR Mobile

Reply 910

Pinkhead

14

Original post by JayJay95

Hey guys, in the book it says take 1u to be 931.3 Mev but on the formula sheet it says 931.5 Mev. Even highlights this on page 183 of nelson thornes examiners tips section.

Any thoughts?

Posted from TSR Mobile

use the formula booklet one.

Reply 911

bugsuper

8

is lens "power" still on the astrophysics syllabus, or did they take it out with the newer spec? thanks

Reply 912

JRP95

2

Original post by bugsuper

is lens "power" still on the astrophysics syllabus, or did they take it out with the newer spec? thanks

They must've taken it out, haven't seen it since 2008 when the spec changed and it's not in the formula book

Reply 913

ehtisham_1

Original post by JayJay95

Hey guys, in the book it says take 1u to be 931.3 Mev but on the formula sheet it says 931.5 Mev. Even highlights this on page 183 of nelson thornes examiners tips section.

Any thoughts?

Posted from TSR Mobile