Understanding Magnetism: Relating Magnetic Forces to Charged Particle Beams"

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In summary, the conversation discusses how to relate magnetic forces to a beam of charged particles moving in a straight line. The participants discuss a guideline question involving the distance and number of particles in the beam, and ultimately determine that the current I carried by the beam is equal to Nvq/L. They also establish a formula for finding the number of particles in a length of v(delta t) and determine how to incorporate it into finding the current I.
  • #1
deanchhsw
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My teacher recently gave me a task of relating magnetic forces to a beam of chraged particles moving in a straight line. To aid us in this, she also set up a guideline question, displayed below:

The diagram below shows a beam of charged particles moving in a straight line with speed v. Each particle has a charge +q and there are N particles in length L of the beam.

(diagram omitted, since the explanation above seems sufficient, direction does not seem to matter here)

a) how far do the particles travel in time "delta t"?
this seemed obvious, s = vt, hence s = v"delta t".

b) how many particles pass a given point in a time "delta t"?
how do you know that? since there is no specific point where a particle begins to travel, how would you know how many passes a random point in a specified time? I thought a lot about this, but can't seem to understand..

c) Using your answers to (a) and (b) above show that the current I carried by the beam is given by the expression I = Nvq/L.

It seems as though the first two equations relate to each other to create the final expression. But I'm lost. I know for memory that I = "delta q"/"delta t", but without knowing what to do for #b) I can't figure anything out.

If anyone could help me, (or at least guide me in the right direction?), I'll be grateful.
 
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  • #2
deanchhsw said:
c) Using your answers to (a) and (b) above show that the current I carried by the beam is given by the expression I = Nvq/L.

It seems as though the first two equations relate to each other to create the final expression. But I'm lost. I know for memory that I = "delta q"/"delta t", but without knowing what to do for #b) I can't figure anything out.

If anyone could help me, (or at least guide me in the right direction?), I'll be grateful.

{----------------------}--------------------------------
A...v(delta t)....B

Suppose my '-' s are the beam... suppose the distance between A and B is v (delta t).

It takes the particle at A delta t seconds to reach B... in that time all the particles within the { } cross B (this is the critical part! in the time that it takes the particle at A to reach B... all the particles that were between A and B at the start cross B)... so all the particles within a length of v(delta t) cross B in delta t seconds.

You know the number of electrons in a length L... so you can get the number of electrons in a length v delta t.
 
  • #3
I see. So since N/L should be equal to n/v(delta t), with n being the answer to #b, doing the math n comes out to be N(v delta t)/L. I understand that now.

But how, then, do you incorporate that to find the current I?
OHH I solved my own question lol

I = delta q/delta t, and delta q is equal to nq, since it is the number of the particles carrying the given charge +q. So substituting nq = delta q,

I = N(v delta t)q/L(delta t), and simplifying, I = Nvq/L.

Thanks, you've been a ton of help! :)
 

1. What is magnetism?

Magnetism is a physical phenomenon in which objects have a force that attracts or repels other objects. This force is created by the movement of electric charges within the object.

2. How do magnets work?

Magnets work by creating a magnetic field, which is a region of space that surrounds the magnet and exerts a force on other magnets or magnetic materials. This force is strongest at the poles of the magnet.

3. What are the different types of magnets?

There are three main types of magnets: permanent magnets, temporary magnets, and electromagnets. Permanent magnets, such as those found in refrigerator magnets, have a constant magnetic field. Temporary magnets, such as iron or steel, can be magnetized when in the presence of a magnetic field. Electromagnets are created by running an electric current through a wire wrapped around a metal core, and the strength of the magnet can be adjusted by changing the amount of current.

4. How is magnetism used in everyday life?

Magnetism has many practical applications in our everyday lives. Some common uses include in motors and generators, speakers, credit cards, and compasses. It is also used in medical imaging technology, such as MRI machines, and in data storage devices, like hard drives.

5. Can you shield or block a magnetic field?

Yes, it is possible to shield or block a magnetic field using materials such as iron, steel, or mu-metal. These materials redirect the magnetic field lines, causing them to loop around the material and weaken the strength of the field. However, it is difficult to completely block a magnetic field, and the strength of the field may still be present on the other side of the shield.

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