How Does Lenz's Law Affect Current in Adjacent Loops?

In summary: So, what direction around the loop does the change in current point? HINT: Right hand rule.If I curl my fingers in the right hand rule, my thumb points towards the side of my hand with the index finger. So the direction of the change in current is in a clockwise direction around the loop.4. Does this change in current increase or decrease the current in the lower loop?Decrease.
  • #1
Lokhtar
12
0

Homework Statement



Two conducting loops carry equal currents I in the same direction as shown in the figure. If the current in the upper loop suddenly drops to zero, what will happen to the current in the lower loop according to Lenz’s law?

(a) The current in the lower loop will decrease.
(b) The current in the lower loop will increase.
(c) The current in the lower loop will not change.
(d) The current in the lower loop will also drop to zero.
(e) The current in the lower loop will reverse its direction.
http://img21.imageshack.us/img21/8688/lenzrz5.jpg

Homework Equations



Lenz's law states "Induced emf resulting from a changing magnetic flux has a polarity that leads to an induced current whose direction is such that the induced magnetic field opposes the original flux change."

The Attempt at a Solution



I know that the answer is (b). I am just trying to figure out why.

Lenz's law is just conservation of energy, so if both currents are going in the same direction, than forces are going upwards? If the top one were removed, wouldn't the force acting on the bottom one decrease? I think I am confusing a bunch of things, but trying to understand how/what to approach this problem.
 
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  • #2
From your statement of lenz's law, the change in current in the top loop will induce an emf and thus a change in current in the lower loop. This change in current creates a magnetic field. The magnetic field will oppose the change in flux caused by the first loop.

So, to answer this question, you need to answer the following smaller questions:

1. What direction does the change in flux caused by the top loop point?

2. The field created from the change in current in the lower loop must point opposite the change in flux. What direction is this?

3. So, what direction around the loop does the change in current point? HINT: Right hand rule.

4. Does this change in current increase or decrease the current in the lower loop?

Can you answer these questions?
 
  • #3
G01 said:
1. What direction does the change in flux caused by the top loop point?

Well, if I use the right hand rule, and curl my fingers towards I, my thumb points straight up.

G01 said:
2. The field created from the change in current in the lower loop must point opposite the change in flux. What direction is this?

Counterclockwise?


G01 said:
3. So, what direction around the loop does the change in current point? HINT: Right hand rule.

Up?

G01 said:
4. Does this change in current increase or decrease the current in the lower loop?

Can you answer these questions?

I think I am missing something conceptually, perhaps with the application of RHR.
 
  • #4
I'm trying to look at the book and trying to visualize the forces, but I don't quite get it.
 
  • #5
G01 said:
1. What direction does the change in flux caused by the top loop point?
Lokhtar said:
Well, if I use the right hand rule, and curl my fingers towards I, my thumb points straight up.
That's the direction of the flux, but the question asks about the change in flux.

I is initially counterclockwise. If it drops to zero, it's change is in the opposite direction. So curl your fingers in that direction.

G01 said:
2. The field created from the change in current in the lower loop must point opposite the change in flux. What direction is this?
Lokhtar said:
Counterclockwise?
The question is about the magnetic field or flux. This will be either up or down. So the question is, what direction--up or down--is opposite to the change in flux you got for question #1?
 

Related to How Does Lenz's Law Affect Current in Adjacent Loops?

1. What is Current and Lenz's Law?

Current and Lenz's Law are two fundamental concepts in electromagnetism that describe the relationship between electric currents and magnetic fields. Current refers to the flow of electric charges through a conductor, while Lenz's Law states that the direction of an induced current will oppose the change that caused it.

2. How does Lenz's Law work?

Lenz's Law is based on the principle of conservation of energy. When a changing magnetic field passes through a conductor, it induces an electric current. This induced current creates a magnetic field that opposes the original change in the magnetic field, in accordance with the law of conservation of energy.

3. What is the significance of Lenz's Law?

Lenz's Law is important because it helps us understand the relationship between electric currents and magnetic fields. It also plays a crucial role in the design and operation of many devices such as generators, transformers, and motors.

4. How is Lenz's Law related to Faraday's Law?

Lenz's Law is a consequence of Faraday's Law, which states that a changing magnetic field will induce an electric field. Lenz's Law specifies the direction of the induced current in relation to the change in the magnetic field, while Faraday's Law quantifies the magnitude of the induced EMF.

5. Can Lenz's Law be violated?

No, Lenz's Law is a fundamental law of physics and cannot be violated. Any change in the magnetic field will always result in an induced current that opposes the change, in accordance with the law of conservation of energy.

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