motor effect questions (1 Viewer)

[superSAIyan2]

Hey guys,

Can someone help me answer this question.

Is the wire moving 45degrees to the magnetic field or is it perpendicular to the field since it is directed downwards. I think its perpendicular but I'm kinda doubtful. Also is the force directed towards bottom right corner?

Thanks

 

[Immortalp00n]

your direction is correct
angle theeta is the angle between the conductor and the external magnetic field.
so I think it'd be safe to say that
F=BIlsin(o)
F=12 x (10 x 10^-3) x 15 x sin(90)
F=1.8 N

 

[bleakarcher]

your direction is correct
angle theeta is the angle between the conductor and the external magnetic field.
so I think it'd be safe to say that
F=BIlsin(o)
F=12 x (10 x 10^-3) x 15 x sin(45)
F=1.27 N

Isn't the angle between the conductor and the direction of the magnetic field 90 degrees? The magnetic field is going directly into the page and the conductor lies on the plane of the page.

 

[Parvee]

The angle is 90 degrees.

You would only use the 45 degrees if the mag field was moving to the left or right of the page

 

[Immortalp00n]

oh yes
that is right
thanks bleak and parbee

 

[bleakarcher]

It can't be 45 degrees because that's not theta. As you said yourself, the angle theta is the angle between the conductor (on the plane of the page) and the direction of the magnetic field (directly into the page). This means theta=90 degrees. If you still don't get it, I'll draw a diagram to explain it a bit better.

 

[Immortalp00n]

It can't be 45 degrees because that's not theta. As you said yourself, the angle theta is the angle between the conductor (on the plane of the page) and the direction of the magnetic field (directly into the page). This means theta=90 degrees. If you still don't get it, I'll draw a diagram to explain it a bit better.

true true
its all good
i misinterpreted the diagram
draw ur diagrom anyways though might solidify the idea

 

[nightweaver066]

Isn't the angle between the conductor and the direction of the magnetic field 90 degrees? The magnetic field is going directly into the page and the conductor lies on the plane of the page.

Yep. Questions like these tend to trick quite a lot of people lol

 

[planino]

That's not how you play noughts and crosses

 

[bleakarcher]

true true
its all good
i misinterpreted the diagram
draw ur diagrom anyways though might solidify the idea

Sure man. Here you go:

 

[Immortalp00n]

Sure man. Here you go:

View attachment 27574

ah alright lol i see why i derped
cheers brah

 

[bleakarcher]

Yep. Questions like these tend to trick quite a lot of people lol

It's probably because it's not taught properly, my own teacher made this same mistake last year when we were learning F=qvBsin(theta) but then I researched it and realised it was wrong. It's funny because he came up with a proof of it thinking theta was the angle between the current and the plane of the page somehow.

 

[nightweaver066]

It's probably because it's not taught properly, my own teacher made this same mistake last year when we were learning F=qvBsin(theta) but then I researched it and realised it was wrong. It's funny because he came up with a proof of it thinking theta was the angle between the current and the plane of the page somehow.

That's one reason, but i reckon after people learn it, they assume it's simple stuff (it really is) and so whenever they encounter a question like this, they see an angle, current + magnetic field and just blindly apply the formula. I lost a mark in one of my exams for this so i learnt this the hard way lol

 

[superSAIyan2]

thanks for the replies guys. and am i right in saying the force will be towards the bottom right?

 

[bleakarcher]

thanks for the replies guys. and am i right in saying the force will be towards the bottom right?

I'd draw an arrow to point out the direction of the force showing that it's perpendicular to the current but I'm not sure about this.

 

[superSAIyan2]

ok thanks

 

[AnimeX]

Hi guys, I'm still a bit confused, how is it 90 degrees?

For example in my diagram, would it still be 90 degrees? and how?

please define " plane of conductor"

 

[leaf-monkey]

if the question does not specify an angle, then it is always 90 degrees( perpendicular) which gives us the maximum force possible in that particular magnetic field.
yeha im pretyy sure B is directed there, but I'm not 100% sure

 

[leaf-monkey]

Yeah some diagrams can be quite confysing but it is perpendicular, if you kinds title your head; look at it in a 3D point of view. Hope this makes sense lol!

 

[Fizzy_Cyst]

Hi guys, I'm still a bit confused, how is it 90 degrees?

For example in my diagram, would it still be 90 degrees? and how?

please define " plane of conductor"

View attachment 27575

Your diagram it would not be 90 degrees as the conductor and the magnetic field lie in the same plane, both are running into/out of page and across page (this is the x/z plane)

Plane refers to the two dimensional slice in which something lies. Think about a classroom, you are facing the board.

Now think about a 3 dimensional graph, x-axis is across page, y-axis is up/down page and z-axis is in/out page.

Apply this to the classroom, the whiteboard runs up/down the wall and across it, hence we say it is in the x/y plane. The roof of the room comes out of the wall and runs across the room, hence it is the x/z plane. Now the sidewalls of the room come out of the front wall and run up/down, hence we say it is the y/z plane.

If the conductor and the magnetic field lie in the same plane, the angle must be used. What I say to my students is if you can replicate the diagram, using the RHP rule, without breaking your thumb, the angle does not matter and is 90deg. If you have to break your thumb, it does matter and don't sue me.