The Student Room Group

PHYA5 ~ 20th June 2013 ~ A2 Physics

Scroll to see replies

Original post by posthumus
Erm I'm not quite sure what your asking exactly but if an Ice cube is dropped into some hot water then most likely... the Ice cubes temperature will rise to 0 degrees, then when it reaches here the energy that goes towards breaking down the inter-molecular forces in the ice, this heat energy does not increase the temperature (no increase in kinetic energy), the amount needed to change the waters state to liquid is known as latent heat of fusion. The energy is still there... it's just not being used as kinetic energy (which contributes to the temperature).

The total energy of the system is the total Kinetic energy + total potential energy stored withing inter-molecular bonds (latent energy if you like)

Hope that makes sense :smile:


So you're saying the latent energy gained by the ice when it chabges state to water is not gained by the water already inside thats losing temperature?
U doubt this is tge case. But I think I didn't understand what you wrote.



Posted from TSR Mobile
Original post by cooldudeman
So you're saying the latent energy gained by the ice when it chabges state to water is not gained by the water already inside thats losing temperature?
U doubt this is tge case. But I think I didn't understand what you wrote.



Posted from TSR Mobile


No the latent heat is only being gained by the ice cube, because it's changing state unlike the water already in liquid form.
Reply 462
Do calculated answers have to match the mark scheme answers precisely? I mean if the MS said 154 but I get 155 will I get the mark?
Reply 463
We had a discussion about sig figs a few pages back. Basically decided that you can only be penalised for rounding errors once per paper, where it tells you sig figs are important

basically it's just good practice to use exact answers wherever possible in the middle of your working - i.e, if you have to multiply by a number you've worked out, use the whole number, not a rounded one, or you'll get errors. use the store/retrieve function on your calculator if the answers are just long strings of decimals.
Original post by posthumus

Also I wouldn't know because I haven't done many past papers, just a few thermal physics questions from the old spec. But I hope if these questions do come up they will be at least 4 marks.. :smile:


Ahh thanks for the help. :smile: I figured out the tricks to these questions. Some questions are not even part of the new spec. So i just do the ones that will most likely come up.
Original post by bugsuper
We had a discussion about sig figs a few pages back. Basically decided that you can only be penalised for rounding errors once per paper, where it tells you sig figs are important

basically it's just good practice to use exact answers wherever possible in the middle of your working - i.e, if you have to multiply by a number you've worked out, use the whole number, not a rounded one, or you'll get errors. use the store/retrieve function on your calculator if the answers are just long strings of decimals.


So we will not loose marks if the answer is 795 and I get 796 as long as my working out is right. Unless they mention correct sf in the question.
One more example is that I multiply 25 x 971= 24275. So do I write it as 24000(2sf) or 24300(3sf).

I did not know that you use the exact worked out answer when you multiply it by something else. Never use the rounded answer if you are going to use it for more working out. :smile:
Reply 466
anyone doing medical physics? :P
Can anyone help with this?

The question asks you to complete an equation for alpha decay and then calculate the energy released.

The u values such as 4.002.... for alpha aren't stated and since it's 5 marks I guess we have to calculate them.

Anyone any idea how I go about calculating the energy released? Here's the question:
http://gyazo.com/6517264176f79c04201dad08727bcdb9
What are the conditions to get an A* in physics again?
Reply 469
Original post by ThatRandomGuy
What are the conditions to get an A* in physics again?


480/600 overall in AS And A2, alongside 270/300 overall in units 4 5 and 6
Original post by JRP95
480/600 overall in AS And A2, alongside 270/300 overall in units 4 5 and 6


Thanks, was hoping the practical wouldn't count :redface:
I have around 2 days (6-8 hours) to teach myself the whole of astrophysics and revise unit 5 once again. How content heavy is the astrophysics part?
Original post by JRP95
480/600 overall in AS And A2, alongside 270/300 overall in units 4 5 and 6


Would that not be 240/300 in the A2 units? I thought it was 90%?
Reply 473
Original post by ThatRandomGuy
I have around 2 days (6-8 hours) to teach myself the whole of astrophysics and revise unit 5 once again. How content heavy is the astrophysics part?


Yeah that can be done, astro is not that content heavy, understand and memorize every page and do questions at the end of a topic, then move on. (you'll need the Collins book though)
Reply 474
Original post by HypErTwisT
Would that not be 240/300 in the A2 units? I thought it was 90%?


Yeah and 90% of 300 is 270
Reply 475
Could anyone give me the suggested voltage values for thermionic emission? I know one's around 100, and the other around 1000.. but I can't remember which is which. Thanks!
Reply 476
When they ask us to state a property on black holes what are they looking for. Do they want us to talk about the event horizon and define it, talk about the event horizon and within ir ot past it. Sometimes I feel like its just random :/
Reply 477
Original post by JakeMachinima
Can anyone help with this?

The question asks you to complete an equation for alpha decay and then calculate the energy released.

The u values such as 4.002.... for alpha aren't stated and since it's 5 marks I guess we have to calculate them.

Anyone any idea how I go about calculating the energy released? Here's the question:
http://gyazo.com/6517264176f79c04201dad08727bcdb9


Hmm, seems like there's part of the question missing? I can't seem to figure out how to do this one :s
(edited 10 years ago)
Reply 478
Original post by JoshL123
When they ask us to state a property on black holes what are they looking for. Do they want us to talk about the event horizon and define it, talk about the event horizon and within ir ot past it. Sometimes I feel like its just random :/


I usually say that a black hole is very dense and has a very large gravitational field. It has an escape velocity greater than the speed of light, c. I think that would suffice for a definition. :smile:
Reply 479
Original post by JakeMachinima
Can anyone help with this?

The question asks you to complete an equation for alpha decay and then calculate the energy released.

The u values such as 4.002.... for alpha aren't stated and since it's 5 marks I guess we have to calculate them.

Anyone any idea how I go about calculating the energy released? Here's the question:
http://gyazo.com/6517264176f79c04201dad08727bcdb9


Yeah you will have to. The U value are on the formula sheet, under the heading of proton. So you calculate the U values for the products and starting materials of the decay, the difference in mu and multiply it by the MeV in 1 U (which is 931.11 or something) :smile:

Quick Reply

Latest