# Homework Help: Current reference direction confusion

1. Jun 7, 2013

### cytochrome

1. The problem statement, all variables and given/known data

I have two questions.

1) The ends of a length of wire are labeled a and b. If the current i from a to b is negative, are electrons moving toward a or b?

2) We have a circuit element with terminals a and b. The voltage and current from a to b are both positive. If electrons carry the charge, which terminal do they enter?

2. Relevant equations
None, this is a conceptual problem.

3. The attempt at a solution
For question 1), I concluded that a negative current from a to b means that electrons flow from a to b. This makes sense and is the correct answer.

For question 2), I concluded that electrons flow from b to a since the positive current goes from a to b, but this is not the answer in the book.

Is the book wrong? Or am I missing something?

2. Jun 7, 2013

### Staff: Mentor

I agree with your answers, since electrons move in the opposite direction of the "positive current". But question 2 is worded a bit loosely, so maybe that is where the disconnect lies.

The statement "The voltage and current from a to b are both positive." is not precise or correct. Voltage from a to b does not make sense. "Voltage drop from a to b" would be precise and correct. Maybe there is some strange voltage inversion because of the imprecise statement? Maybe it's a voltage source instead of a sink like a resistor?

3. Jun 7, 2013

### CWatters

For 2) I believe the circuit element must be a battery or voltage source.

If "b" is the +ve terminal of the source and "a" the negative then it makes sense.

The voltage a -> b is +ve.
The current flowing within the source/battery is also from a -> b.

..so I agree with your answer. Electrons flow from b to a.

Last edited: Jun 7, 2013