# Magnetic force on a charge carrying wire

• thatgirlyouknow
In summary, when a wire is attached to the N surface of a very broad magnet, the current will keep the magnet rotating.
thatgirlyouknow
[SOLVED] Magnetic force on a charge carrying wire

## Homework Statement

A current carrying wire is in a magnetic field as shown below. The magnet is on a scale. Given this setup, does the scale read more or less weight? Explain using the Right Hand Rule and Newton's Third Law. Note: The apparatus depicted is a magnet sitting on the mass pan of a balance.

## Homework Equations

The RH rule is a bit long to explain here.. basically, the current is flowing W, and the magnetic force is N to S.

Newton's 3rd: For every action, there is an equal and opposite reaction.

## The Attempt at a Solution

The wire is carrying current, but the current is not given. Current must be positive, so therefore it has a charge of >0. Positive current exerts a force upward based on the drawing, so the magnet will weigh less. I don't know how to explain this in terms of the RH rule, though. My best guess:

With my thumb pointing in the direction of the current and fingers wrapped around the wire, the magnetic force flows N to S. My open palm would face left? right? up? down?, which corresponds to the force the magnet will feel. Because of Newton's Third Law, the weight will _____.

#### Attachments

• magnet.jpg
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So if the magnetic force on the wire is upward, then the magnet itself will push downward, resulting in a weight gain.

Right?

Right. If the magnet pushes the wire up, the wire pushes the magnet down--increasing its apparent weight.

Awesome. Thanks for the help!

Doc Al said:
Right. If the magnet pushes the wire up, the wire pushes the magnet down--increasing its apparent weight.

Hmm... What if a wire is attached to the N surface of a very broad magnet? Now if the current is switched on, and the whole setup is free to rotate on a wheel, what will happen? Will the BIL force continue to rotate the wire with the magnet for as long as the current flows?

## 1. What is the magnetic force on a charge carrying wire?

The magnetic force on a charge carrying wire is the force exerted on the wire by a magnetic field. This force is perpendicular to both the direction of the magnetic field and the direction of the current in the wire.

## 2. How is the magnetic force calculated?

The magnetic force on a charge carrying wire can be calculated using the formula F = qvBsinθ, where q is the charge of the particle, v is the velocity of the particle, B is the strength of the magnetic field, and θ is the angle between the velocity and the magnetic field.

## 3. What is the direction of the magnetic force?

The direction of the magnetic force on a charge carrying wire is determined by the right-hand rule. If the thumb of your right hand points in the direction of the current in the wire, and your fingers point in the direction of the magnetic field, then the palm of your hand will point in the direction of the magnetic force.

## 4. How does the magnetic force affect the motion of the wire?

The magnetic force on a charge carrying wire can cause the wire to move in a circular or helical path, depending on the angle between the wire and the magnetic field. If the wire is parallel to the magnetic field, there will be no magnetic force and the wire will not move.

## 5. What factors affect the strength of the magnetic force?

The strength of the magnetic force on a charge carrying wire depends on the strength of the magnetic field, the charge and velocity of the particle, and the angle between the velocity and the magnetic field. The magnetic force will increase if any of these factors increase.

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