Question Involving h/mv (1 Viewer)

[allGenreGamer]

Here is a question that I have:

- Find the de Broglie wavelentgh of a proton which has been accelerated through 65V, if mass of proton = 1.82 * 10^-26 kg and the charge on an electron = 1.6 * 10^19 C

It'd be fine if someone could just tell me which formulas to use... I should be able to do the working out, I simply do not know what equations to use! Thanks.

P.S. Can someone give me instructions on how to delete a thread ?

 

[mojako]

not sure about ur question, but
to delete a thread, click on EDIT first. then at the top there will be an option to delete the thread.

 

[leginag]

are u sure it is of a proton??
i was under the impression that De Broglie's law thingy only worked for electrons
in which case u would use wavelength(landa) = h/p = h/(mv)

 

[xiao1985]

are u sure it is of a proton??
i was under the impression that De Broglie's law thingy only worked for electrons
in which case u would use wavelength(landa) = h/p = h/(mv)

de broglie's proposal would mean that all matters exhibit wave particle duality ... hence it can apply to all matters... (or waves for that matter)

 

[wogboy]

- Find the de Broglie wavelentgh of a proton which has been accelerated through 65V, if mass of proton = 1.82 * 10^-26 kg and the charge on an electron = 1.6 * 10^19 C

1. You're told the proton is accelerated through 65V -> use K = V*Q to find the kinetic energy of the particle after it has been accelerated.
2. Use the formula K = (1/2)*mv^2 to determine the final speed v of the particle.
3. Use p = mv to determine the final momentum of the particle.
4. Then you can use lambda = h/p (or equivalently h/mv), to work out the De Broglie wavelength.

 

[chazza]

1. You're told the proton is accelerated through 65V -> use K = V*Q to find the kinetic energy of the particle after it has been accelerated.
.

hey man.. how does kinetic energy = voltage times charge??
care to explain
thanks..

 

[wogboy]

hey man.. how does kinetic energy = voltage times charge??

Suppose a particle of charge Q is in an electric field of strength E.

F = Q*E (the force on the particle)
but E = - dV/dx (V is the electric potential, x is position)
F = -Q*dV/dx
Now W = Integral{x1 -> x2} F dx (W is the work done by the field on the particle to move it from x1 to x2)
W = - Integral{x1 -> x2} Q*dV/dx dx
= -Q * Integral{x1 -> x2} dV/dx dx
= -Q * {V(x2) - V(x1)}

By the conservation law of energy, the work done by the field on the particle equals the increase in kinetic energy of the particle, by being accelerated in that field (K = W)

K = -Q*(V(x2) - V(x1))
K = -Q*D
(where D is the change in electric potential, K is the change in kinetic energy)

 

[mojako]

or, without calculus,
on the first page of the formula sheet you have E = F/q, i.e. F = E*q (where * is times)
on the second page you have E = V/d
combining, F = V/d*q
but work = force*distance
E_k = V*q

note: the email notification was sitting on my inbox and I hadn't bothered going to wogboy's answer due to its scary nature
I post this just to show that it can be done without calculus.

 

[Xayma]

Or you could just remember that a particle with a charge of an electron is given one electron volt of energy when passing through a potential difference of 1V.

 

[Jase]

They should consider putting that into the formulae sheet. Since they spoonfeed us all the other formulae, its only fair we get this one.. i was completely lost when you started with the calculus, and im hardly familiar with that eqaution..

Is this all the same as, finding the work done in moving a charge over a potential diference?
i.e. W=qV

 

[mojako]

it is, hehe..
but is W = q V in the formula sheet?
I can't find it

I think it's a good idea to omit some formulas

 

[Xayma]

But they give you what an electron volt is. From there it is just a matter of multiplying by appropriate numbers.

Eg 2V on a particle with a charge of 2 electrons (eg an alpha particle) will gain 4eV.