- #1
skweeegor
- 2
- 0
Homework Statement
Ernest Rutherford in his lab at McGill University, Montreal, fired alpha particles of mass 6.64 * 10^-27 kg at gold foil to investigate the nature of the atom. What initial energy must an alpha particle (charge +2e) have to come within 4.7 * 10^-15 m of a gold nucleus (charge +79e) before coming to rest? This distance is approximately the radius of the gold nucleus.
Givens:
m = 6.64 * 10^-27 kg
q_alpha = 2(1.6 * 10^-19 C)
= 3.2 * 10^-19 C
q_gold = 79(1.6 * 10^-19 C)
= 1.264 * 10^-17 C
r_gold = 4.7 * 10^-15 m
d = 4.7 * 10^-15 m
r = r_gold + d
= 9.4 * 10^-15 m
k = 9.0 * 10^9 N*m^2/C^2
Homework Equations
E = kq1q2/r
The Attempt at a Solution
So I know that the total energy of the system when the alpha particle is at rest and r distance from the centre of the gold nucleus is given by the equation E = kq1q2/r.
So, E = [(9.0*10^9)(3.2*10^-19)(1.264*10^-17)] / 9.4 * 10^-15
Which gives me E = 3.87 * 10^-12 J
However, this is exactly half of what the solution should be, and I can't seem to figure out why.
Thanks