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Who's doing crappy Advancing Physics OCR B?

I can't quite remember the question, but I think it's because the deuterium nucleus needs enough kinetic energy to overcome the electrostatic repulsion between it and the tritium nucleus. They need to come close enough together that the strong nuclear force comes into effect and overpowers the repulsion (thereby fusing the nuclei). Since the electrostatic repulsion between nuclei is so strong, you need a lot of energy to allow it to get close enough.

Reply 121

sunspoon

14

dbox

I can't quite remember the question, but I think it's because the deuterium nucleus needs enough kinetic energy to overcome the electrostatic repulsion between it and the tritium nucleus. They need to come close enough together that the strong nuclear force comes into effect and overpowers the repulsion (thereby fusing the nuclei). Since the electrostatic repulsion between nuclei is so strong, you need a lot of energy to allow it to get close enough.

Thats pretty much what I wrote. Plus something about quantum tunnelling just for good measure. :smile:

Reply 122

dbox

sunspoon

Thats pretty much what I wrote. Plus something about quantum tunnelling just for good measure. :smile:

Ooh, good point. I remember that from one of the old Advances in Physics papers actually.

Can anyone shed any light on the neutron number question? What confuses me is that it said you need a number of neutrons released greater than one, which surely means the nuclear reactor is going supercritical? I would have thought that you'd want the average number of neutrons released to be one for a "stable chain reaction", i.e. one that is at critical mass?

Reply 123

sunspoon

14

Well the problem with only releasing one neutron is that you have to keep firing neutrons yourself to speed up the reaction.

By having more than one neutron released the chain reaction increases in speed by itself with each fission, and therefore you can vary the speed you want the reaction to go at by lowering/removing the moderator as you so please, which works because only neutrons slowed down by the moderator can induce the fission of another nucleus... :smile:

Reply 124

AdvancedWave

sunspoon

Well the problem with only releasing one neutron is that you have to keep firing neutrons yourself to speed up the reaction.

By having more than one neutron released the chain reaction increases in speed by itself with each fission, and therefore you can vary the speed you want the reaction to go at by lowering/removing the moderator as you so please, which works because only neutrons slowed down by the moderator can induce the fission of another nucleus... :smile:

I wrote something along those lines. The paper wasn't too bad, some of the questions were a bit confusing. Like the one were you had to work out the electrical potential energy of the one (of two) palladium nuclei.

Reply 125

sunspoon

14

Really? Was it EPE then? I swear I read it as just potential ... which would just be -kQ/r - oh well - iv got biology synoptic to look forward to tomorrow :biggrin:

Reply 126

Ecno

1

From the sound of the answers here I've absolutetly ****ed up royal the FPP which is really dissapointing because I think I did really well in the RFCU but FPP combined with my poor coursework will most likely mean I won't be getting an A unless my PIA retakes goes up to nearly full UMS (unlikely as I know I've droped atleast 4 marks out of 90) or I get like 110 in the synpotic which is perhaps more unlikely.

Reply 127

AdvancedWave

sunspoon

Really? Was it EPE then? I swear I read it as just potential ... which would just be -kQ/r - oh well - iv got biology synoptic to look forward to tomorrow :biggrin:

Ahh, I struggle to remeber my name sometimes, you're probably right. I do remeber the -kQ/r bit though :smile:

Reply 128

luopangwang

sunspoon

Really? Was it EPE then? I swear I read it as just potential ... which would just be -kQ/r - oh well - iv got biology synoptic to look forward to tomorrow :biggrin:

By the way, isn't the potential energy E=QV

Reply 129

lawrywild

The answer was 4.4MV x 46 for the kinetic energy question.

I stupidly did 4.4MV x 46 x 1.6x10^-19 and then didn't divide by 1.6x10^-19 again so I left my answer in Joules..

Reply 130

Happyness

14

Does someone have the actual answer to that electric potential question which said show that its 4 mega volts? and part b of it asking for the potential energy? And why was that 5 marks altogether?

Also say you get High C, Low B and your coursework is 36/40. Would that bring the overall mark upto mid-B for FPP module?

Reply 131

luopangwang

Dose anybody know how much does corsework account for in the second year

Reply 132

luopangwang

In 2863, there is one question asked you to find out the root mean square of one gas molecule.
We are supposed to work it out by using formula 1/2mv^2=3/2 KT

But I couldn't remember the formula, I used one on the formula book instead, and I got the right answer.
the formula I used was pV=3/2mv^2
Would that be correct

Reply 133

dave345

i did the same, was the answer 2000ms-1

Reply 134

AdvancedWave

Happyness

Does someone have the actual answer to that electric potential question which said show that its 4 mega volts? and part b of it asking for the potential energy? And why was that 5 marks altogether?

The formula to use was (I think!!) EPE = -kQ/r , and you get 4.04 mega volts.

Reply 135

Happyness

14

it asked for the electric potential not EPE. also r was 1.45x10^-15 and the others are constant so its doesnt coe out to 4 mega volts

I have worked so hard in physics and yet they make some questions which doesnt have much to do with any of the spec. For e.g look a few 2865 "explain that" questions.