When doing a magnetic problem, when they say current do we assume positive or negative?

[sillyjoe]

I'm confused because I thought current was negative. I know the convention for fields etc. is designated for positive charges. However, I always assumed when they used the word current, they meant negative charge.

For example, EK physics 1001 Question 889 states:

It seems to me like they are assuming that current is positive? Any clarification of the conventions I should be using would be much appreciated.

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[lNVlNClBLE]

You can assume current is positive. Current flow is always opposite the direction of electron flow, which is just a standard convention made up a long time ago.

 

[sillyjoe]

You can assume current is positive. Current flow is always opposite the direction of electron flow, which is just a standard convention made up a long time ago.

So unless they specify, when they use the word current I should assume positive charge? What about when dealing with circuits?

 

[pepocho]

.

 

[sillyjoe]

Current is always dealing with the direction of positive to negative. current is easily confused with "direction of electron flow" Yes, you can technically say that current IS electron flow. But just because the guys who studied current said so, when they say current is where the positive go. So when they say the direction is counterclockwise. The positive is going counterclockwise. HOWEVER, electron flow is going the opposite way, in this case clockwise. It takes a while to get used to. hell I still catch myself forgetting that. Especially when the question tricks me and ask for the direction of the electrons.

So this applies in circuitry etc?

 

[pepocho]

.

 

[orangetea]

hmm that's weird I assumed it was just a single electron (negative) and got the same answer.

 

[sillyjoe]

hmm that's weird I assumed it was just a single electron (negative) and got the same answer.

How? If you use your left hand (electrons) the answer would have been B. Look at the picture and try the same motion for wire 1 with your left hand.

 

[orangetea]

How? If you use your left hand (electrons) the answer would have been B. Look at the picture and try the same motion for wire 1 with your left hand.

I use the "right hand rule" differently. my fingers are the current my palm is the magnetic field and my thumb is the electric field... so left hand fingers to the left thumb is pointing up and palm faces away from you right? that means magnetic field is going into the page.

 

[sillyjoe]

I use the "right hand rule" differently. my fingers are the current my palm is the electric field and my thumb is the electric field... so left hand fingers to the left thumb is pointing up and palm faces away from you right? that means magnetic field is going into the page.

Can you please edit your post? I think you made your palm and thumb the same vector quantity.

 

[orangetea]

okay better now?

 

[sillyjoe]

If you use your left hand the way described, I think your force vector is going in the wrong direction?

 

[orangetea]

poop

 

[sillyjoe]

poop

For these problems you should really modify your right hand rule since you need a circle. THIS IS THE BEST VIDEO FOR RIGHT HAND RULE I HAVE FOUND.

Make sure to watch the entire video because he discusses wires at the end:

 

[sillyjoe]

poop

And just in general it is an excellent channel. Really really good.