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PSA6 - Can you help with questions from a past paper? watch

1. If anyone can suggest the answers to these, I'd appreciate it. They're mathsey ones, so I'm hoping for only one answer to each (I want to eliminate my confusion, not add to it)!

(All from PSA6, June 2004)

1. Calculate the temperature at which Flourine-17 ions would have energies equivalent to having been accelerated from rest by 25MV. The charge on a Flourine-17 ion is -1.6x10-19.

[Other numbers given in the passage in the start of that question are: the half-life of Flourine-17 is 64s. (I don't know whether you'd have to use these)]

2. The table shows the radius r of various atomic nuclei of nucleon number A.

Element..........Nucleon Number (A).......Nuclear Radius (r/10-15 m)
Boron........................... ....10.......................... .2.69
Silicon......................... ......28........................ ..3.93
Strontium....................... ....88.......................... 5.34
Tin............................. ......120....................... ...5.99
Uranium......................... ...238.........................7 .74

It is predicted that for most nuclei r=r0A1/3

a) Plot a suitable graph to confirm this relationship.

(I could do part a), the log-log graph)

b) Use the graph to determine a value of r0

c) The mass of a nucleus is directly proportional to its nucleon number. Assuming the shape of a nucleus can be approximated to a sphere, and that r=r0A1/3, show that the density of nuclei of different elements should be the same.

d) A nucleus of fluorine containing 17 nucleons has a radius of 5.5x10-15m. Use your graph to predict how it's density compares to that of other nuclei.

Any light people can shed on these would be much needed illumination!
2. what exam board is that?
3. Answer to q1 is 1.93*10^11 K
using eV=1/2mv^2 and 1/2mc^2=3kT/2
therefore eV=3kT/2
4. for question 2 your dont need to do a log graph
it is better to plot the nuclear radius against A^1/3 which will give you a straight line then r0 is equal to the gradient

for part c:

density =mass / volume

mass of nucleus is proportional to the nucleon number there for we can say m=A

and the volume of a sphere is 4/3(pi)r^3

therefore

density=A/(4/3(pi)(r0A^1/3)^3)
cancelling out

density=1/(4/3 (pi) r0^3)

note the density does not rely on the nucleon number therefore density should be the same for different elements as r0 is constant.

sorry its so hard to follow its kinda hard to type maths on the computer, any problems with understanding post back and ill try to explain in more detail.
5. Question 1 solution:

First you need to convert energy to Joules. So:
25Mev = (25*10^6) * 1.6*10^-19 = 4*10^-12 Joules

Now use E= (3/2)*KT, where K is boltzman constant

T= 1.93*10^11 Kelvin
6. has anyone done the psa6 june 2002 past paper im stuck on q1g

'calculate the magnitude of the 'small force' refferred to in the passage. [2]

i know you use F=BIl but not sure how to find B.

The passage at the front of the paper is photocopied badly so does not sure if it gives a value in that. if not can someone give me a hand.
cheers
7. (Original post by nicnewell)
Answer to q1 is 1.93*10^11 K
using eV=1/2mv^2 and 1/2mc^2=3kT/2
therefore eV=3kT/2
Is that formula 3kT/2 a standard one? Trying to find formulae in the salters book is like finding a needle in a haystack. Secondly, what value does k have?
8. (Original post by nicnewell)
for question 2 your dont need to do a log graph
it is better to plot the nuclear radius against A^1/3 which will give you a straight line then r0 is equal to the gradient

for part c:

density =mass / volume

mass of nucleus is proportional to the nucleon number there for we can say m=A

and the volume of a sphere is 4/3(pi)r^3

therefore

density=A/(4/3(pi)(r0A^1/3)^3)
cancelling out

density=1/(4/3 (pi) r0^3)

note the density does not rely on the nucleon number therefore density should be the same for different elements as r0 is constant.

sorry its so hard to follow its kinda hard to type maths on the computer, any problems with understanding post back and ill try to explain in more detail.
Okay i understand the density part but if m is directly proportional to A, why is m=A and not =kA where k is the proportionality constant?

Furthermore - isn't a log-log graph used to show power relationships? I plotted it and got the straight line - I just don't know how to use it. I figured gradient but the logs are confusing me... once again, trying to decipher Salters context-based cufuffle doesn't do any favours!

I'd appreciate more help on this, because once i understand it, it does tend to stick!
9. One last query... it's 20MV not 20MeV in the q.
10. (Original post by nicnewell)
has anyone done the psa6 june 2002 past paper im stuck on q1g

'calculate the magnitude of the 'small force' refferred to in the passage. [2]

i know you use F=BIl but not sure how to find B.

The passage at the front of the paper is photocopied badly so does not sure if it gives a value in that. if not can someone give me a hand.
cheers
30 µT...yes, it does say in the passage. I have the answer scheme too, so if you want to check your answer, just let me know.

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