Motors and Generators Question (1 Viewer)

[Sp3ctre]

https://gyazo.com/3dd4212847ef84559688ff7fabfd8754

I thought the answer was C but the correct answer is A? I thought by using the right hand palm rule, your fingers point into the page and your palm points down the page, so your thumb is pointing to the left. Since your thumb represents flow of conventional current (or positive charge), shouldn't the negative charge or electrons be on the opposite side, i.e. the right?

 

[jazz519]

Right hand palm rule is used for positive particles. For the negative particles such as an electron you need to use the left hand palm rule (same thing as right hand palm rule but just with ur left hand)

 

[Sp3ctre]

Right hand palm rule is used for positive particles. For the negative particles such as an electron you need to use the left hand palm rule (same thing as right hand palm rule but just with ur left hand)

It's the same thing, if you use right hand palm rule then you just take the direction of the negative charge to be away from your thumb. Using left hand palm rule stills gives me the wrong answer.

 

[jazz519]

It's the same thing, if you use right hand palm rule then you just take the direction of the negative charge to be away from your thumb. Using left hand palm rule stills gives me the wrong answer.

I think you might have mixed up the position of the hand. Your fingers point in the direction of the magnetic field, so into the page. Your palm faces the direction of the force on the particles and your thumb will go in the direction of the velocity

 

[Sp3ctre]

I think you might have mixed up the position of the hand. Your fingers point in the direction of the magnetic field, so into the page. Your palm faces the direction of the force on the particles and your thumb will go in the direction of the velocity

That's what I'm doing but if I use the left hand palm rule like you suggested, my thumb would point to the right, then that means electrons are flowing to the right, but that's not what the answer agrees with.

 

[jazz519]

That's what I'm doing but if I use the left hand palm rule like you suggested, my thumb would point to the right, then that means electrons are flowing to the right, but that's not what the answer agrees with.

The greatest concentration of electrons is the direction the force is pointing not the thumb

 

[Sp3ctre]

The greatest concentration of electrons is the direction the force is pointing not the thumb

Oh, why is it that? Plus if that is the case, the answer would still be different.

 

[pikachu975]

Oh, why is it that? Plus if that is the case, the answer would still be different.

The force points to the left using left hand palm rule so the electrons are at excess to the left.

 

[jazz519]

Oh, why is it that? Plus if that is the case, the answer would still be different.

I'm not sure what you are doing with ur hand, but your fingers need to put point into the screen and ur thumb points downwards so that means your palm faces to the left which is the answer A.

It is because if there is a force on the particles in a certain direction more of them will move to that direction because of the acceleration caused by the force

 

[Sp3ctre]

I'm not sure what you are doing with ur hand, but your fingers need to put point into the screen and ur thumb points downwards so that means your palm faces to the left which is the answer A.

It is because if there is a force on the particles in a certain direction more of them will move to that direction because of the acceleration caused by the force

Oh I kind of see what you mean now. I'm still not too clear on why your thumb needs to point downwards in the first place though. When it shows that PQRS is moving downwards I thought that it was because of the applied force that was causing it to move downwards, thus I had my palm pointing downwards instead of my thumb.

 

[jazz519]

Oh I kind of see what you mean now. I'm still not too clear on why your thumb needs to point downwards in the first place though. When it shows that PQRS is moving downwards I thought that it was because of the applied force that was causing it to move downwards, thus I had my palm pointing downwards instead of my thumb.

In this question, we are not like really considering the rod, this q is basically like doing a q where there is a single electron and they ask you what direction it will move and in those Qs we use the velocity as the thumb

 

[Sp3ctre]

In this question, we are not like really considering the rod, this q is basically like doing a q where there is a single electron and they ask you what direction it will move and in those Qs we use the velocity as the thumb

Right, I understand now. It just seems weird that the velocity of the rod is referring to the direction of electrons rather than the movement of the rod as a whole as a result of an applied force. Thanks for your help anyway!

 

[Sp3ctre]

I'm such an idiot, I just realised the direction of the arrow was labelled I -_-