# Transformers: Uniform magnetic filed in relation to current flow

• dba
In summary: Thanks!The direction of the change in flux is the direction opposite of the direction of the magnetic field.
dba

## Homework Statement

In our lab about transformers we have a question as follows:
Consider a loop in a uniform magnetic field. If the field is suddenly turned off, in which direction will the current flow in the wire?

## The Attempt at a Solution

My first thought was that if there is no current then there is no magnetic field but I am not sure. Thanks for any hint.

Currents are induced by the loop experiencing changes in the magnetic field, and in particular, changes in the magnetic flux within the area circumscribed by the loop.

Look up Faraday's law and Lenz's Law.

You will have to determine the direction of the change in flux that takes place when the field is switched off, and then determine the resulting direction of the induced current.

Can you explain a little better what you mean by the direction of the change in the flux? For the problem, there are no numbers. There is a vertical loop and the direction of the field is to the right. The flux is the integral of B*A since B and da are parallel and A is pi*r^2. Thanks!.

The flux is the integral of B*da, and in this case since B starts out at some constant value, and since A is also constant, the flux is B*A.

If you were to represent the original flux as a vector pointing through the loop plane, it would be pointing in the direction of the magnetic field B (to the right, since that's the direction that you said that B points). What happens when the whatever is supplying B field is switched off? The B field collapses to zero, right? What then will be the direction of the change in flux?

That is exactly what I do not understand. I do not know how to imagine a direction of a change. As I mentioned in the beginning, I would assume if my B goes to zero, then the flus will be zero and the current will be zero. therefore there would't be a direction.

dba said:
That is exactly what I do not understand. I do not know how to imagine a direction of a change. As I mentioned in the beginning, I would assume if my B goes to zero, then the flus will be zero and the current will be zero. therefore there would't be a direction.

Often the interesting stuff happens while things are changing, not after they've changed

Before the field's disappearance the flux is B*A and is comprised of magnetic field lines of B, which have a definite orientation while passing through the plane of the loop. So when the field collapses, it's as though you're adding a counter-flux to oppose and cancel the flux of the B field. That is to say, the flux change is in the direction opposite that of B. The magnitude of that flux change is B*A if the field goes to zero.

## 1. What is a uniform magnetic field?

A uniform magnetic field is a type of magnetic field where the strength and direction of the magnetic field is constant throughout the entire space. This means that there are no variations in the magnetic field's strength or direction at any point.

## 2. How is a uniform magnetic field created?

A uniform magnetic field can be created by passing an electric current through a straight wire or by using a permanent magnet. In both cases, the magnetic field lines will be parallel and equally spaced, resulting in a uniform magnetic field.

## 3. What is the relationship between current flow and a uniform magnetic field?

Current flow refers to the movement of electric charges, and when current flows through a conductor, it creates a magnetic field around the conductor. In a uniform magnetic field, the direction of the current flow is perpendicular to the direction of the magnetic field lines.

## 4. How does a uniform magnetic field affect objects within its space?

Objects that are placed in a uniform magnetic field will experience a force known as the Lorentz force. This force is perpendicular to both the direction of the current flow and the magnetic field lines, and it can cause objects to move or rotate.

## 5. What are some applications of uniform magnetic fields?

Uniform magnetic fields are used in a variety of technologies, including electric motors, generators, and particle accelerators. They are also used in medical devices such as MRI machines and in the study of magnetic materials and their properties.

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