# Hints needed.

Can anyone give some hints on this problem?
This is about current and resistance.

Problem: A steady beam of alpha particles (q= +2e) traveling with constant kinetic energy 20MeV carries a current of 0.25 micro ampere.
(a) If the beam is directed perpendicular to a plane surfece, how many alpha particales strike the surface in 3.0s?
(b) At any instant, how many alpha particles are there in a given 20 cm length of the beam?
(c) Through what potential difference was it necessary to accelearte each alpha particle from rest to bring it to an energy of 20 MeV?

Thanks,

ShawnD
Originally posted by xerox2ooo
Problem: A steady beam of alpha particles (q= +2e) traveling with constant kinetic energy 20MeV carries a current of 0.25 micro ampere.
(a) If the beam is directed perpendicular to a plane surfece, how many alpha particales strike the surface in 3.0s?
Remember what an ampere is? That's coulombs per second. Just start multiplying stuff until the units work out the way you want them to.

$$(\frac{coulomb}{second})(seconds)(\frac{\alpha}{coulomb})$$

coulombs and seconds will cancel out and you're left with the number of alpha particles.

(b) At any instant, how many alpha particles are there in a given 20 cm length of the beam?
This one I don't know.

(c) Through what potential difference was it necessary to accelearte each alpha particle from rest to bring it to an energy of 20 MeV?

$$E = Vq$$

$$V = \frac{E}{q}$$

E is 20MeV, q is 2e

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Originally posted by ShawnD
Just start multiplying stuff until the units work out the way you want them to.
That always seems to work.

Thanks guys.

You guys are the best.