# Electric Potential Difference

1. Jun 7, 2013

### andy.tsang

1. The problem statement, all variables and given/known data
A generator has an output of 240V. It is intended to operate machinery some distance away. If the machinery has to operate on 25A and the cables carrying the current have a total resistance of 5.0Ω. find the PD across the ends of the cables. Will the machinery operate?

2. Relevant equations

3. The attempt at a solution
240 - PD = 5*25
PD= 240-125=115V

not sure if my answer is correct?

2. Jun 7, 2013

3. Jun 7, 2013

### anhnha

Hi,
I'd like to know what is inside the machine that make sure the machine operate at 25A?
I mean how can we assure that the machine will operate at 25A.

4. Jun 7, 2013

### Staff: Mentor

The question doesn't give enough information to specify precisely the makeup of the machinery. You have to "take it as given" that the machine draws 25A.

If you were to interpret the question to mean that the machinery is supposed to draw 25A at 240V, you might surmise that it is a resistive load of 240V/25A = 9.6Ω. But "machinery" often implies that there's a motor involved, which would imply that at least part of the load is inductive in nature (motors have windings to produce magnetic fields). If the load is purely inductive you could determine its impedance (reactance) if it is assumed to draw an apparent current of 25A at 240V.

How you interpret the given information depends upon the context of the coursework: course level and material covered in the course.

5. Jun 7, 2013

### anhnha

Thanks, I wanted to understand the meaning of these given information in reality.

6. Jun 7, 2013

### andy.tsang

Thanks Gneill and Anhnha.