AQA Physics A unofficial mark scheme 12/01/12

Hi guys, just a thread to compare answers and try and get answers for all of the questions. If you can remember what you got then post it here. This was my 3rd attempt :biggrin:

In terms of the percentage question in the electricity part, I got 22.2%
I don't know how on earth I did it.. but most other people seem to have got the same.
It said 5 minutes, so I converted that to 300 seconds. Then I multiplied 300 by 9 to get 2700 - the energy with no waste
Then I multiplied 300 by 7 to get 2100, the energy after you take away the internal resistance of 2ohms.
Then 2100/2700 x 100 = 77.8% or something, 100-77.8 = 22.2%
I could be wrong though

---------------------------------------------------------------------------------- General consensus

Q1 - Table - It was a Proton and a Pi+ meson. Charge of all of them were +1. Strangeness of -1 for one of them.
- part ii) name a particle and its antiparticle that's a baryon? (I think) Proton and antiproton
- part iii) name the quark structure of an anti baryon = 3 antiquarks
- part iv) name a similarity and difference in antiparticle/particle = same mass, but opposite charge/baryon number/lepton number

Q2- What is specific charge? it is the charge/mass, measured in Ckg^-1
- How many protons and Neutrons? = 4 protons, 6 Neutrons

Q3 - Concept of pair production? = photon creates particle/antiparticle pair if it has required energy for both particles.
*- momentum and something is conserved, name 2 other things conserved = lepton number, charge, baryon number etc

Q4 - ground state? = lowest energy level that an electron can be
- difference between ionisation and excitation? = ionisation remove electron, excitation moves to higher energy level
- frequency of photon required to ionise? = 13.6eV * 1.6*10^-19 all divided by h which was about 3x10^15 or something.
- Only certain photons can cause excitation because the electrons in each atom exist at discrete energy levels, the energy absorbed by the electron must be exactly equal to the difference in energy levels for excitation to occur or the photon is deflected, so there must be specific excitiation energies, as frequency is directly proportional to energy by e=hf there must be specific frequencies of photon that can provide exactly this amount of energy

Q5 - Long question

Q6 - Critical temperature = the temperature at which at and below there is zero resistivity
- Current readings? = 0.44A and 3.0A

Q7- Percentage question = 22.2%
-Internal resistance = 2 ohms
-Why is it an advantage to have low internal resistance in a rechargeable battery? = less energy wasted when charging/takes less time to charge

(edited 12 years ago)

Scroll to see replies

Reply 1

anuradha_d

I can say that the voltage across R1 was 12, and r2 was 7.5 xD and one of them had 7 ohms and one had 17 i think :/

Also, critical temp is basically the temperature at and below which a material can superconduct ie. no resistance. Above the critical temp, this property is lost.

Reply 2

aliman65

I must have got a previous question on this wrong because I got 1900 not 2100. So I got 33.3% I think. I think I am going to have to re-sit unless the grade boundary for an A drops to below 50%

Reply 3

Sam-8

why dont we try doing this going through the questions.....

1i. the table
ii i believe was name a particle and its antiparticle that is a brayon???
iiii name the structure of a antibaryon?

people just edit and add questions they know until we try to get all the questions. :biggrin:

Reply 4

ieatcheeseyo

I'll try to remember my answers...I'll post when I do
Anyone else (thinking) or going to resit?

Reply 5

Shaz_am

DAMMIT, I thought this was the unofficial markscheme!

Reply 6

Astonix

Answer to question about X and Y atoms is 4 protons, 6 neutrons.

I worked out the Specific Charge of X, then divided it by 1.25 for Specific Charge of Y as this was stated in the question.

I then re-arranged SP = C / kg to C = SPkg. I worked out the mass of Y as 10 nucleons is just 10(1.67*10^-27), and SP I had.

Once I had C, I divided it by the charge of protons to work out how many there was, which was 4. Then 10-4=6 which must be neutrons

(edited 12 years ago)

strangeness -1?

Some more answers that I put..

What is the quark structure of an antiparticle or something? I put 3 antiquarks

Difference between ionisation and excitation - I put that ionisation occurs when a photon of energy has the required energy hf to remove the electron completely from the atom, excitation moves the electron to a higher energy level but does not remove it completely.

Describe the process of pair production - I put it's when a photon with enough energy forms a particle and its corresponding antiparticle, only if the photon has the energy equal to both particles.

Strangeness was -1

the wavelength was some number x10^15m

EDIT - I will try and edit the first post and include all of the answers if people can remember them and the question number

(edited 12 years ago)

Reply 9

anuradha_d

Original post by Sam-8

why dont we try doing this going through the questions.....

1i. the table : pion+, +1 for all charges and baryon numbers that we had to fill, and -1 for strangeness
ii i believe was name a particle and its antiparticle that is a brayon??? this was easy, you can say proton and anti-proton, etc
iiii name the structure of a antibaryon? three anti quarks.

people just edit and add questions they know until we try to get all the questions. :biggrin:

There

Reply 10

EmmaJane_

Last question:
Why is it an advantage to have low internal resistance in a rechargeable battery:
Answer: so less energy is wasted when charging/takes less time to charge etc.

Reply 11

anuradha_d

For difference between Ionisation and Excitation, I said this for 3 marks:

Excitation is when an electron gains energy from a collision/absorption and moves to a higher energy level from ground state
Ionisation involves the same as the above, except in this case, the electron gains enough energy to be removed from the atom.

Pair production: A photon interacts with matter (eg. a nucleus) and converts into a particle and its anitparticle, with the net change in energy being zero, and all the conservation laws (eg. charge momentum) being conserved.

Whaddya think?

Reply 12

EmmaJane_

There was also that huge question about the resistance of a wire when between 0 and 100 degrees. Not gonna give a model answer for that one because I doubt I got full marks!

Reply 13

Member737,514

For critical temp, would it suffice to say- the temperature at which the metal becomes a superconductor (ie Resistance =0)

Reply 14

mar junior

Original post by Astonix

Answer to question about X and Y atoms is 4 protons, 6 neutrons.

I worked out the Specific Charge of X, then divided it by 1.5 for Specific Charge of Y as this was stated in the question.

I then re-arranged SP = C / kg to C = SPkg. I worked out the mass of Y as 10 nucleons is just 10(1.67*10^-27), and SP I had.

Once I had C, I divided it by the charge of protons to work out how many there was, which was 4. Then 10-4=6 which must be neutrons

1.5, why not 1.25? it said that the SC of the first nucleus was 1.25 times more than the nucleus Y

Reply 15

Member737,514

Pair production- converting energy into matter. When a high energy, fast moving photon turns into a particle and it's antiparticle. The photon must have the energy equivalent of the rest mass of the particle x 2.

Reply 16

emmzie_x

crap i put +1 for the strangness without thinking, was so hard i think! if someone comes up with an unoffical mark scheme pls let me know

Reply 17

Astonix

Original post by mar junior

1.5, why not 1.25? it said that the SC of the first nucleus was 1.25 times more than the nucleus Y

Ah yer, it was 1.25. Thanks for pointing it out

Reply 18

Shaktal

Original post by Member737,514

That's approximately right; but you should have stated the mass-energy equivalence principle: E = mc^2

Energy of a photon: E = hf

Therefore hf >= 2mc^2, where m is the rest mass of the particle, must be true if pair production is to occur.

Reply 19

emmzie_x

Original post by EmmaJane_

There was also that huge question about the resistance of a wire when between 0 and 100 degrees. Not gonna give a model answer for that one because I doubt I got full marks!