# Homework Help: Hints needed.

1. Mar 24, 2004

### xerox2ooo

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,

2. Mar 24, 2004

### ShawnD

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.

This one I don't know.

$$E = Vq$$

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

E is 20MeV, q is 2e

Last edited: Mar 24, 2004
3. Mar 24, 2004

### Chen

4. Mar 24, 2004

### Chen

Re: Re: Hints needed.

That always seems to work.

5. Mar 24, 2004

### xerox2ooo

Thanks guys.

You guys are the best.