Question

d) A rectangular wire loop is held in place near a long Straight wire that has an AC current. The current in the top wire alternates. The direction of Positive Current is indicated. Consider the times 0.25 % and Which of these times will have an induced current? For those that do, determine its direction. Which of these times have a net force on the loop? Which direction?

good reasons please

Answer 1

a) An anternating current creates an anternating voltage (EMF) in the closed circuit (rectangular loop):

$\Phi$ =magnetic flux through the closed area

emf varies opposite with I in time.

The first question is improperly asked. You cannot have an induced current as long as you don't have a changes in the flux (another varying current, varying surface, moving 'receptor' circuit, etc). In this case the varying linear current produces the emf in the rectangular loop (only in the webs parallel with the linear curent).

So, the only thing that can be said is:

Consider only the emf graph, and take time on 0x axis instead of angle. The emf graph is opposite with I: when Imax, emf is minim (-emf max), but 0 points are the same for these 2 parameters.

What is important is the observations made at the maximum and 0 points of emf:

- "most rapid rate of change at 0 point..."

- "most rapid rate of change at peak amplitude...."

b) When I increases (0-0.5sec) B increases, and induces a Bi that is opposite with it in the closest parallel web (with the linear I) of the rectangular wire.

The situation for (0.5-1) sec of I is opposite than that illustrated in the figure above.

As long as a varying current is present in the linear wire, we'll have forces on the parallel webs of the rectangular loop.