AQA Physics PHYA5 - 28th June 2016 [Exam Discussion Thread]

Can anyone remmeber how many marks was in question 5 and how they were split up for each ? I`m a bit panicy as i got the first part wrong and carried my answer onto the rest, will there be marks awarded for error carried forward?

Thanks

Hi!

Are you referring to the nuclear section of the paper or your chosen option?

I'm going to assume Nuclear - Question 5 was basically first calculating the energy required to melt 0.047kg of ice (ALREADY AT 0 degrees) given it's Latent Heat of Fusion. The next part was calculating the energy used to heat the ice from -25 degrees to 0, given the total energy supplied to it.

The final part asked you to calculate the Specific Heat Capacity of Ice using your first 2 parts, which was done by using Q = mc(delta)T, rearranging for c and using your Q value from the second part

Hope it helps!

Hey Thanks Bud for replying,

So yeah can you remember the marks for each ? I think the second part was one, final part was three. First part- not sure? maybes 1 ? i put the wrong value in my calculator for part 2 , read 1550 instead of 15500 (such an idiot) hence i carried that answer onto the rest and did exactly all that method plus the correct specific heat capacity units for the final one. I got a large specifc heat that i spent ages thinking thats definitely not right but had to move on . Would I be awarded error carried forward marks do you think ?

Im desperate for an A in physics gawd

It was 4 marks because the equation isn't given, so you either have to know the equation or the derivation for it. It asked you to calculate the specific charge given some values of B, r and V - it never asked anything about deriving it. They will probably give marks for derivation, but also the mark scheme will likely say "If 1.9x10^11 Ckg^-1 seen, 4 marks". They can't take marks away because you know the equation MORE than other people, that'd be completely nonsensical.

Yeah I know, what I was trying to say was since you needed to do quite a bit of work if you didn't know the equation off by heart already, it was worth 4 marks (as it may take people longer to derive it).

Yeah, I understand I think they definitely expected some people to derive it, and that'll be the bulk of the marks so that if you get it wrong, you still get marks for derivation, but I think they'll just give 4 marks for seeing the answer 1.9*10^11 with the correct units.

You'd definitely get error carried forward, so long as the method behind your thinking was correct. Luckily, I looked up a few numbers before the exam to remember, and I knew that ice had a specific heat capacity of 2100. So long as for part ii) you did 18000 (I think that was the given value, but basically the value they gave you) minus your answer for part i), then used your answer from part ii) to calculate heat capacity by rearranging the equation, you'll probably get all the marks except the 1 you messed up at the start Sometimes AQA can be harsher, but I can assuredly say you'll get at LEAST 3 marks from the 5.

Part i) was one mark, ii) was one mark and iii) was 3 marks

for 2 of the assumptions of an ideal gas question in section A out of the 2 marks would this get any
fixed mass of gas
at a constant temperature

Ahh thanks so much for this !! Yeah same! I was so confused at the end like "thats surely not the specific heat capacity" and checked over it a few times but astro was waiting so had to move on and thought its aqa so they might do something weird like this haha . So I put down 1550 , then did 18000- 1550 to get 16450 then divided that by ( 0.047 x 25 ) mass x temp difference and it came out with 14000.

Also for the volume one earlier i didnt realise the temp change hence got the wrong volume. I then used that on the density part to get 1.5 but the working was the same and the mass part correct ? can you remember how many marks those questions were split into? I think it was i) 2, then ii) 1 then iii) 2 maybes 3?

I never realized how error carried forward worked? most of our past test were just right or wrong marks. Do you have to get the right final answer for all the marks? or can you still get all the marks on say that final part of the specific heat capacity question regardless aslong as you do the method 100% correct?

Sorry thats a lot to answer to but thank you so much

for 2 of the assumptions of an ideal gas question in section A out of the 2 marks would this get any
fixed mass of gas
at a constant temperature

(since these are the assumptions for boyles law and it says ideal gases follow boyles law completely)

also for question about causes behind increasing radiation, i said increasing exposure to cosmic background radiation. I however didn't explain this is because of ozone depletion because the question didn't specify that you had to give a reason why this factor was increasing
would i probably still get that mark?

Hi again! Sorry I took a while to respond

For the part about volume, I really can't say for sure if you'll get error carried forward marks - the problem was, the question asked for the initial density, so you had to use the volume they already gave you in the question, which was 0.0016m^3, if you remember. They might give you 1 mark for the correct method of calculating density (using mass divided by volume), but I think considering you've used the final volume, they won't give error carried forward marks for not calculating the initial density, unfortunately. Sorry

Error carried forward is an absolute godsend, and as you said, I've noticed the same thing - when I've done exams in school, if I got it wrong they'll mark it so and my grade will be bad because I made a mistake in 1 question and it messed up all the rest, but in the actual exams, every question which relies on a previous calculation will say ECF from part (x) in the mark scheme, which basically means that so long as your method is correct in the next part, and the only thing wrong is your actual value from the previous part of the question, you'll get the marks.

As an example, if there's a question split into 5 parts and it's worth 10 marks in total, each 2 marks, if you get the first part wrong and the rest all rely on that answer to calculate the answers to them, provided your method is correct on the next 4, despite the actual answers being wrong, you will certainly get at least 8 of those 10 marks.

In Unit 2 last year, I managed to make a huge mistake in my calculations for a mechanics question, and I really couldn't see what I'd done wrong - the next 4 parts of the question required you to know the first part's answer, so I just literally put in the first section "=8ms^-1", and then used 8 in all the next parts - I got error carried forward on all the next parts and got all marks except the =8 one!

Good luck!

Hey thanks for replying and clearing that up for me!

Aw thats okay , can you remember how many marks that question was split up into? sure i got the mass bit right- i honestly think im overthinking this exam now like. I`m hoping its gone okay

Thanks

You had to add 40 back on as there would still be background detected by the detector, I think you'll only drop 1 mark

I don't think you need to add the 40 because it didn't say his detected count rate was the corrected count rate