Direction of Current in a Sliding Bar

In summary, current goes from positive to negative because that is how the convention for current flow is established.
  • #1
patrickbotros
34
1
I'm studying for the Physics SAT Subject Test using The Princeton Review (2011-2012). There's this motional EMF problem about a rod sliding to the right along a u-shaped wire in a uniform magnetic field that's going into the page and the current moving counter clockwise. Problem is: I can't figure out why the current is going counter clockwise. It seems to me that the magnetic force would push electrons in the rod downwards, creating a negative end on the bottom. Therefore, current would go from positive to negative so it would be clockwise, right?
 
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  • #2
patrickbotros said:
Therefore, current would go from positive to negative so it would be clockwise, right?

current = electrons, go from negative to positiveDave
 
  • #3
If the electrons go down, the conventional current goes up, which means counter-clockwise for the complete circuit.

The current goes from plus to minus in the external circuit. In the source it goes from minus to plus, to close the loop. Here the moving bar is the source.
 
  • #4
nasu said:
If the electrons go down, the conventional current goes up, which means counter-clockwise for the complete circuit.

The current goes from plus to minus in the external circuit. In the source it goes from minus to plus, to close the loop. Here the moving bar is the source.
Why would the current go from positive to negative? Isn't current the motion of electrons? Why is it in the opposite direction elections go? Is this just a convention or is there a reason?
 
  • #5
Yes, it is a convention. Look up "conventional current".
 
  • #6
patrickbotros said:
Why would the current go from positive to negative?

you did state that in you opening post ...

patrickbotros said:
I can't figure out why the current is going counter clockwise. It seems to me that the magnetic force would push electrons in the rod downwards, creating a negative end on the bottom. Therefore, current would go from positive to negative so it would be clockwise, right?

when current flow was discovered, it was long before electrons were discovered and that they moved from neg to pos
As Nasu said do some googling on convention current flow and electron flow :smile:Dave
 

FAQ: Direction of Current in a Sliding Bar

What is the direction of current in a sliding bar?

The direction of current in a sliding bar depends on the direction of motion of the bar. If the bar is moving horizontally, the current will flow in the same direction as the motion of the bar. If the bar is moving vertically, the current will flow in the opposite direction of the motion of the bar.

How is the direction of current in a sliding bar determined?

The direction of current in a sliding bar is determined by the right-hand rule. This rule states that if you point your right thumb in the direction of the bar's motion, your fingers will curl in the direction of the current.

Does the direction of current in a sliding bar change if the bar is in a magnetic field?

Yes, the direction of current in a sliding bar can change if the bar is in a magnetic field. This is because the magnetic field can exert a force on the bar, causing it to move in a different direction and thus changing the direction of the current.

What factors can affect the direction of current in a sliding bar?

Besides the direction of motion and the presence of a magnetic field, other factors that can affect the direction of current in a sliding bar include the strength of the magnetic field, the speed of the bar's motion, and the material of the bar.

What is the significance of the direction of current in a sliding bar?

The direction of current in a sliding bar is important because it determines the polarity of the bar. This polarity can affect the behavior of the bar in a magnetic field and can also determine the direction of the force exerted on the bar. It is also important in understanding the principles of electromagnetism and the operation of devices such as electric motors and generators.

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