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Urgent - Please Help!!!
hey.
we've been set these questions in school for HW - but they're super hard. we're only 1st year AS students and we're doing stuff this complex!
if anyone can give any help (i believe its just knowing the formulas), i'd really appreciate it.
Questions:
1. In Rutherford's famous scattering experiments that led to the planetary model of the atom, alpha particles (charge +2e, mass = 6.64 x 10-27 kg) were fired at a gold nucleus (charge +79e). An alpha particle, initially very far from the gold nucleus, is fired with a velocity of 4.80 x 107 m/s directly toward the center of the nucleus. How close does the alpha particle get to this center before turning around? Assume the gold nucleus remains stationary.
Answer: ? fm
2.Suppose that 1000 alpha particles of kinetic energy 5.00 MeV deflect by more than 30 degrees when a beam of alpha particles strikes a very thin foil of gold. How many of these particles will deflect by more than 40 degrees?
b(>=30°) = ? m
*small sigma*(>=30°) = ? m^2
b(>=40°) = ? m
*small sigma*(>=40°) = ? m^2
N(>=40°) = ?
* *small sigma* looks like an o with a horizontal line coming out of it.
we've been set these questions in school for HW - but they're super hard. we're only 1st year AS students and we're doing stuff this complex!
if anyone can give any help (i believe its just knowing the formulas), i'd really appreciate it.
Questions:
1. In Rutherford's famous scattering experiments that led to the planetary model of the atom, alpha particles (charge +2e, mass = 6.64 x 10-27 kg) were fired at a gold nucleus (charge +79e). An alpha particle, initially very far from the gold nucleus, is fired with a velocity of 4.80 x 107 m/s directly toward the center of the nucleus. How close does the alpha particle get to this center before turning around? Assume the gold nucleus remains stationary.
Answer: ? fm
2.Suppose that 1000 alpha particles of kinetic energy 5.00 MeV deflect by more than 30 degrees when a beam of alpha particles strikes a very thin foil of gold. How many of these particles will deflect by more than 40 degrees?
b(>=30°) = ? m
*small sigma*(>=30°) = ? m^2
b(>=40°) = ? m
*small sigma*(>=40°) = ? m^2
N(>=40°) = ?
* *small sigma* looks like an o with a horizontal line coming out of it.
Reply 1
14
I can't remember if this is correct, haven't done physics for a while:
You take the total kinetic energy of the Alpha particle, so use 0.5mv2
Then use the formula:
V=(Qq)/(4piEr)
Where V equals the KE worked out before, Q is the charge of the alpha particle, q is the charge of the gold nucleus. E is the permeability of free space, I think the value is 8.85 x10^-12. And r is the distance of closest approach.
I get the answer to be 4.766 x 10-15m or 4.766 fm
If its wrong, feel free to correct me. :P:
You take the total kinetic energy of the Alpha particle, so use 0.5mv2
Then use the formula:
V=(Qq)/(4piEr)
Where V equals the KE worked out before, Q is the charge of the alpha particle, q is the charge of the gold nucleus. E is the permeability of free space, I think the value is 8.85 x10^-12. And r is the distance of closest approach.
I get the answer to be 4.766 x 10-15m or 4.766 fm
If its wrong, feel free to correct me. :P:
Reply 2
JayEm
I can't remember if this is correct, haven't done physics for a while:
You take the total kinetic energy of the Alpha particle, so use 0.5mv2
Then use the formula:
V=(Qq)/(4piEr)
Where V equals the KE worked out before, Q is the charge of the alpha particle, q is the charge of the gold nucleus. E is the permeability of free space, I think the value is 8.85 x10^-12. And r is the distance of closest approach.
I get the answer to be 4.766 x 10-15m or 4.766 fm
If its wrong, feel free to correct me. :P:
You take the total kinetic energy of the Alpha particle, so use 0.5mv2
Then use the formula:
V=(Qq)/(4piEr)
Where V equals the KE worked out before, Q is the charge of the alpha particle, q is the charge of the gold nucleus. E is the permeability of free space, I think the value is 8.85 x10^-12. And r is the distance of closest approach.
I get the answer to be 4.766 x 10-15m or 4.766 fm
If its wrong, feel free to correct me. :P:
what does the distance of closest approach (r) mean and how do you calculate it?
also the unit 'e', as in an alpha particle has a charge of 2e, in Coulombs? therefore, would an alpha particle have a charge of 3.2 x 10^-19C?
Reply 3
14
The distance of closest approach is what you want to work out. You know all the other values.
V = Kinetic Energy of the Alpha particle
Q = Charge of Alpha particle = 2 x 1.602 x 10-19
q = Charge of gold nucleus = 79 x 1.602 x 10-19
E = is just some constant 8.85 x 10-12 if I remember correctly
4pi is just 4 times pi.
Stick it all in the formula and rearrange it to find r.
V = Kinetic Energy of the Alpha particle
Q = Charge of Alpha particle = 2 x 1.602 x 10-19
q = Charge of gold nucleus = 79 x 1.602 x 10-19
E = is just some constant 8.85 x 10-12 if I remember correctly
4pi is just 4 times pi.
Stick it all in the formula and rearrange it to find r.
Reply 4
cheers, mate. 
why is it that you've used r instead of r^2, which is the formula seen in some of the books?
why is it that you've used r instead of r^2, which is the formula seen in some of the books?
Reply 5
14
There's 3 different fomulas (formulae?) which are related to this subject. One is the force between 2 charged particles (in Newtons), the second is the electric field strength (in NC-1?) and the third is the electrical potential (in Joules). The first 2 use r2 but the third one uses just r. I chose the third one as we're dealing with energies.
Reply 6
ffs howcomes we neva learnt this in AS lol!
Reply 7
14
This is A2 AQA physics, don't know about other exam boards.
Reply 8
Yes, this is A2 Physics - also on Edexcel syllabus.
Does anyone know how to do question 2?
Does anyone know how to do question 2?
Reply 9
Pm sent
Reply 10
8
senny99
hey.
we've been set these questions in school for HW - but they're super hard. we're only 1st year AS students and we're doing stuff this complex!
if anyone can give any help (i believe its just knowing the formulas), i'd really appreciate it.
Questions:
1. In Rutherford's famous scattering experiments that led to the planetary model of the atom, alpha particles (charge +2e, mass = 6.64 x 10-27 kg) were fired at a gold nucleus (charge +79e). An alpha particle, initially very far from the gold nucleus, is fired with a velocity of 4.80 x 107 m/s directly toward the center of the nucleus. How close does the alpha particle get to this center before turning around? Assume the gold nucleus remains stationary.
Answer: ? fm
2.Suppose that 1000 alpha particles of kinetic energy 5.00 MeV deflect by more than 30 degrees when a beam of alpha particles strikes a very thin foil of gold. How many of these particles will deflect by more than 40 degrees?
b(>=30°) = ? m
*small sigma*(>=30°) = ? m^2
b(>=40°) = ? m
*small sigma*(>=40°) = ? m^2
N(>=40°) = ?
* *small sigma* looks like an o with a horizontal line coming out of it.
we've been set these questions in school for HW - but they're super hard. we're only 1st year AS students and we're doing stuff this complex!
if anyone can give any help (i believe its just knowing the formulas), i'd really appreciate it.
Questions:
1. In Rutherford's famous scattering experiments that led to the planetary model of the atom, alpha particles (charge +2e, mass = 6.64 x 10-27 kg) were fired at a gold nucleus (charge +79e). An alpha particle, initially very far from the gold nucleus, is fired with a velocity of 4.80 x 107 m/s directly toward the center of the nucleus. How close does the alpha particle get to this center before turning around? Assume the gold nucleus remains stationary.
Answer: ? fm
2.Suppose that 1000 alpha particles of kinetic energy 5.00 MeV deflect by more than 30 degrees when a beam of alpha particles strikes a very thin foil of gold. How many of these particles will deflect by more than 40 degrees?
b(>=30°) = ? m
*small sigma*(>=30°) = ? m^2
b(>=40°) = ? m
*small sigma*(>=40°) = ? m^2
N(>=40°) = ?
* *small sigma* looks like an o with a horizontal line coming out of it.
I have to say tho that this is the most evil AS question I've ever seen (with regards to question 2).
Reply 11
Its not an AS question at all! Rutherfords formula and cross sections arent on any A level syllabus I know. Its strictly qualitative stuff and closest approah calculations.
THis is the best site for this stuff.
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
THis is the best site for this stuff.
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
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- Y12 work experience (creative or cat related)
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- URGENT student studio apprtment available
- I’ve been accepted into the OIC-COMSTECH & University of Lahore scholarship program.
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