How Does Changing Resistance Affect Induced Current Direction in Nested Loops?

In summary, the direction of the current induced in the small circular loop inside the larger loop will be counterclockwise as the flux through the loop decreases. However, if the small loop is placed outside the larger one to the left, the direction of the current will be clockwise as the flux outside the loop is decreasing in that direction. The direction of the field and its change outside the loop is what determines the direction of the induced current.
  • #1
meganw
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Homework Statement



(a) If the resistance of the resistor in the figure below is slowly increased, what is the direction of the current induced in the small circular loop inside the larger loop?
(b) What would it be if the small loop were placed outside the larger one, to the left?

c0826c28da63693ccf1b08caed5fae05.jpg


Homework Equations



V = IR
E (emf) = d(flux)/dt
flux = B(perp.) * A

The Attempt at a Solution



I know we have to use the right hand rule, but I think I must be doing it wrong.

For a, we know that B must be decreasing becase I is decreasing (and B = u(o) * I(encl.)/dl)

According to Lentz's law, if the flux(B*A) is decreasing then the induced current will have the same field as the other. So in order for both fields to be pointing out as they are, the current must go in the counterclockwise direction in the inner loop.

for part b though, I use the right hand rule and get the same thing-counterclockwishe? But the answer says its clockwise. I don't understand. The flux of the large loop is still decreasing, so doesn't that mean the fields again point in the same direction? That would be both pointing outward. If I use my RHR that I know, in order for the B field to be pointing in the same direction of the induced current, it must go counterclockwise.

Is there something to be said for the fact that it is outside of the loop?

Thanks!
 
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  • #2
What matters is the flux through the small loop and how it is changing. In what direction does the field point just outside and to the left of the big loop? (That's where the small loop would be for part b.) How is it changing?
 

Related to How Does Changing Resistance Affect Induced Current Direction in Nested Loops?

1. What is a magnetic field?

A magnetic field is a region in space where a magnetic force can be detected. It is created by moving electric charges, such as electrons, and is represented by lines pointing from the north to the south pole.

2. How does the B field change?

The B field can change in several ways, including through the movement of electric charges, changes in temperature or pressure, and the presence of other magnetic fields.

3. What causes the B field to change?

The B field can change due to the movement of electric charges, which creates a magnetic field around them. It can also be influenced by the Earth's magnetic field, as well as external forces such as solar winds or magnetic storms.

4. How does the B field affect objects?

The B field can affect objects in various ways depending on their properties. It can cause objects to move, align or repel based on their magnetic properties. It can also protect objects from charged particles in space, such as those in the Earth's magnetosphere.

5. Can the B field be controlled or manipulated?

Yes, the B field can be controlled and manipulated through various techniques such as using electromagnets or changing the direction of electric currents. This is useful in many applications, such as in medical imaging and particle accelerators.

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