# Are induced currents created by motion or change in flux?

• Kerrigoth
In summary, induced currents are caused by a change in magnetic flux, either through motion of the conductor in a magnetic field or a moving magnetic field. Emf is induced when there is a change in flux, and current only flows when the conductor is moved perpendicular to the magnetic field. Lenz's Law states that the direction of the induced current will oppose the change in magnetic flux.
Kerrigoth
The book I am working through is beginning to dive into induced currents and Lenz's Law.

When a conductor is moving perpendicular to a magnetic field, the charge carriers inside will experience a magnetic force; This causes the charges to move. Eventually, the electric field from the charge separation will be so strong that the electric forces on the charges will be equal and opposite to the magnetic force. The presence of an electric field implies an electric potential difference. The epd is commonly known as a motional emf for this specific type of scenario...Slap on some wires and you get a current.

So now let's say I drop a magnet through a loop of wire. The relative motion of the field lines and the charges inside the conductor are parallel; The charges should not be experiencing a magnetic force, hence no motional emf. But nonetheless an induced current occurs.

My book introduced induced currents by demonstrating motional emf. But now we have moved onto Lenz's Law and motion does not seem to matter. Only changes in magnetic flux seem to matter. Even by changing the strength of a stationary magnet, an induced current will occur in a stationary coil.

I'm having a hard time identifying the why the current occurs simply because of a change in flux. It seems like motion can explain it, but only when the conductor is moving perpendicular to the magnetic field.

Kerrigoth said:
So now let's say I drop a magnet through a loop of wire. The relative motion of the field lines and the charges inside the conductor are parallel; The charges should not be experiencing a magnetic force, hence no motional emf. But nonetheless an induced current occurs.

draw yourself a pic of your setup so you can see that the field lines and conductor are not always parallel
come to some conclusions about that

Kerrigoth said:
I'm having a hard time identifying the why the current occurs simply because of a change in flux. It seems like motion can explain it, but only when the conductor is moving perpendicular to the magnetic field.

The change in flux is going to be caused by motion, either ...
1) moving magnetic field or ...
2) moving conductor in a magnetic field

either way the conductor is going to experience a change in fluxDave

A change in the magnetic flux or motion of a conductor in a magnetic field does not induce current, but emf. Say you have a transformer with varying flux through the iron-core (through the secondary windings) and the secondary windings are not loaded by anything, no current will flow through the secondary windings, but you can measure voltage across the windings. Ohms law then states that if you close a loop ( loading the secondary windings by some resistor ) a current will flow: I = V / R. Current flows in closed loops.

Emf = dΨ/dt , where Ψ is the flux passing through a closed loop.

Now, say you have a closed loop formed as a rectangle ABCD. AB and CD are arranged parrallel, and so is BC and AD. If you move this rectangle in a homogeneous magnetic field, the sum of induced emf's in the four sides of the rectangle will be zero, emfAB = -emfCD and so on. Thus the current through the rectangle will be zero.

But if you move only one side of the rectangle perpendicular to the magnetic field, say AB, the sum of the emf's will not be zero and a current will flow. You may say this is due to the conductor AB being moved in the magnetic field, or you may say that when moving only one side (AB), the area of the rectangle must be increased/decreased and thus the flux through the rectangle.

Last edited:

## 1. What are induced currents?

Induced currents refer to the flow of electric charge within a material or an electrical circuit that is caused by a changing magnetic field. This can occur when there is relative motion between the magnetic field and the material or when there is a change in the magnetic flux through the material.

## 2. How are induced currents created?

Induced currents are created by either motion or change in flux. When there is relative motion between a magnetic field and a material, the magnetic flux through the material changes, which induces a current. Similarly, when there is a change in the magnetic flux through a material, it also induces a current.

## 3. What is the difference between induced currents created by motion and change in flux?

The main difference between induced currents created by motion and change in flux is the cause of the changing magnetic field. Motion-induced currents are caused by the relative motion between a magnetic field and a material, while flux-induced currents are caused by changes in the magnetic flux through a material.

## 4. What are some common examples of induced currents?

Some common examples of induced currents include generators, transformers, and electric motors. In these devices, the relative motion between a magnetic field and a conductor or a change in the magnetic flux through a conductor induces a current, which is then used to generate electricity or produce mechanical motion.

## 5. What is the significance of induced currents in everyday life?

Induced currents play a significant role in our everyday lives as they are essential for the functioning of many devices we use. Some examples include electricity generators, transformers, electric motors, and even wireless charging technology. They also play a crucial role in the production of electricity from renewable sources, such as hydroelectric power and wind turbines.

• Electromagnetism
Replies
9
Views
2K
• Electromagnetism
Replies
4
Views
1K
• Electromagnetism
Replies
7
Views
2K
• Electromagnetism
Replies
10
Views
3K
• Electromagnetism
Replies
1
Views
1K
• Electromagnetism
Replies
7
Views
1K
• Electromagnetism
Replies
4
Views
1K
• Electromagnetism
Replies
27
Views
1K
• Electromagnetism
Replies
20
Views
1K
• Electromagnetism
Replies
2
Views
872