How does magnetic field bend Cathode Rays (1 Viewer)

[Mr_Kap]

How does magnetic field bend Cathode Rays.

So if you put a magnet next to the maltese cross, how is the shadow going to be deflected?

 

[DepressedPenguino]

Isn't it right hand palm rule?

 

[Mr_Kap]

Isn't it right hand palm rule?

Um. But what happens to the shadow?

 

[Mr_Kap]

anyone?

 

[Drsoccerball]

How does magnetic field bend Cathode Rays.

So if you put a magnet next to the maltese cross, how is the shadow going to be deflected?

The shadow doesn't get deflected you're mixing up two experiments. Thomson's experiment where he used a magnetic field to find out the charge to mass ratio is different to the malteese cross experiment in which they tried to show that cathode rays travel in straight lines and produces shadows.

 

[addybrah]

what do you mean by the shadow?
if you mean the path of the electron, you use the right hand rule.

A common trick in HSC questions is where they get you to find the direction of the force. Make sure you point your thumb opposite the direction of motion of the cathode ray - because cathode rays are electrons, and the direction of the thumb in RHR is for conventional (ie positive) current.

 

[Mr_Kap]

http://4.bp.blogspot.com/-Pkd-nQpu8ec/UcKwNkxw9_I/AAAAAAAABxs/mMBaZt7xUMs/s1600/Maltese3.png

What about shown in picture? what would happen to the shadow

 

[Drsoccerball]

http://4.bp.blogspot.com/-Pkd-nQpu8ec/UcKwNkxw9_I/AAAAAAAABxs/mMBaZt7xUMs/s1600/Maltese3.png

What about shown in picture? what would happen to the shadow

you'll see the top half of the shadow only as the electron is pushed upwards

 

[porcupinetree]

you'll see the top half of the shadow only as the electron is pushed upwards

This is what would be expected; however, I remember that a few months ago our teacher gave us a past paper with this exact question. I argued exactly what drsoccerball said. My teacher then pulled out a discharge tube with a maltese cross and actually did the experiment - and startlingly, the shadow was pushed downwards when the electron beam was deflected upwards (and vice versa). I don't really understand why this happened though

 

[Drsoccerball]

This is what would be expected; however, I remember that a few months ago our teacher gave us a past paper with this exact question. I argued exactly what drsoccerball said. My teacher then pulled out a discharge tube with a maltese cross and actually did the experiment - and startlingly, the shadow was pushed downwards when the electron beam was deflected upwards (and vice versa). I don't really understand why this happened though

can you quote the paper i want to answer

 

[porcupinetree]

can you quote the paper i want to answer

I can't remember exactly what paper it was, but it was a MC question which showed a shadow of a maltese cross, and basically said "a magnetic field is applied in X direction, what happens to the shadow"

 

[keepLooking]

Also, solutions says A is the answer.

 

[DepressedPenguino]

Also, solutions says A is the answer.

Yeah, the electrons get deflected upwards

 

[Drsoccerball]

Yeah, the electrons get deflected upwards

No the electrons deflect downwards. And since the magnetic field is after the cross the downwards deflection of the electrons would cause the shadow to move down.

 

[Librah]

Also, solutions says A is the answer.

There's not enough information really, or it's just given in a really ambiguous way.

You need to know the direction of the cathode rays (negative charge), and from that image, how are you supposed to know if your looking at the cross from inside of the tube or standing on the outside and viewing the cross? You can't tell if the cathode rays are going into or out of the page.

Also another thing i'm guessing they are assuming is that the magnetic field lines point horizontally and don't form loops at that distance.

But by that set up and according to the answer, the cathode ray has to be going into the page if the cross moves down as the cathode rays are deflected down along with it. (By right or left hand rule)

 

[mrpotatoed]

In that MC it has to be A though regardless of if you look from the front or behind since its the 'most correct answer' and the other 3 are clearly wrong/more wrong.