[mrinformant]

Open to all,
Question = find direction of force?
The diagram shown is a cathode ray tube with maltese cross inside, a bar magnet is being moved down on top of the tube (south end first).
Its obviously magnetic deflection of cathode ray I'm just not too sure how to relate north and south of bar magnet with negative beam of electrons in order to find the direction of force on the particles.

Any help would be great?
cheers

[Unknown008]

How do you determine the direction of a magnetic field? You place a small north pole in front of a magnet, and the direction it does gives the magnetic field direction. The small north pole will be repelled by the north pole of your magnet, so, the direction of your magnetic field is from the north pole of your magnet to its south pole.

Now that you know the direction of the magnetic field, you need to find the direction if the current involved. The conventional current direction is considered to be from a positive terminal of a battery to its negative terminal, or the movement of positive particles from the positive terminal to the negative terminal. Electrons are negatively charged, hence the current is flowing in the opposite direction of the direction of electrons.

Now, you need to know how to use Fleming's left hand rule. You can Google it, you'll get lots of information about it. From there, you'll see that the resultant force will be towards the right. If the north pole was being moved instead, the force would be towards the left.

I hope it helped! :)

[mrinformant]

O yea thankss, I use the right hand screw rule, part that helped most was the placing of small north pole in front of magnet -------- hence the magnetic field is going up the page and force is 'right' into the page thanks