# Understanding Magnetic Forces: Direction, Calculation, and Applications

• scorpa
In summary, the force on a current carrying wire in a magnetic field is down out of the palm of your hand.
scorpa
Hello,

I was doing some bonus homework questions and hit a few snags along the way. Any help would be appreciated!

1) What is the direction of the force on a current carrying wire in a magnetic field if the current is toward the left on a page and the magnetic field is down the page?

For this one I was thinking that the force was down out of the palm of your hand but I wasn't sure.

2) What is the force on a 3.5m long wire that is carrying a 12A current if the wire is perpendicular to Earth's magnetic field?

The thing that is screwing me up in this question is the lack of information given. I have the length and the current given, but to find the force magnetic I also need the magnetic field strength (B). I'm not quite sure how to figure it out without be given the three variables of magnetic force.

A galvanometer has a full-scale deflection when the current is 50.0 uA. If the galvanometer has a resistance of 1.0 kiloohms, what should the resistance of the multiplier resistor be to make a voltmeter with a full-scale deflection of 30.0V?

I thought that I was doing this one right but my answer didn't coincide with the one in the book. This is what I did:

V/I = R 30V / 50x10^-6 A = 6.0 x 10^5 ohms total

(1/Rtotal) - (1/R1) = (1/R2)

(1/600 Kohms) - (1/1 kohms) = 600/599 = (599/600ohms) which is wrong.

Problem 1)

Remember the magnetic force is defined as:

$$\vec{F}_{B} = q \vec{v} \times \vec{B}$$

Thus, by using the right hand rule, if the current is flowing on the left of the page then you must put your fingers pointing left and then close then towards the magnetic field, and then your thumb will point out of the page or on the Z positive axis, imagining the page is the xy plane.

Ok thanks, I'll give that one a try. Anyone got any ideas for the others?

## 1. What is the direction of magnetic forces?

The direction of magnetic forces is always perpendicular to the direction of the magnetic field lines. This means that the force will act at a right angle to the path of the charged particle or current carrying wire.

## 2. How do you calculate magnetic forces?

The formula for calculating magnetic forces is F = qvBsinθ, where F is the force, 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 particle's velocity and the direction of the magnetic field.

## 3. What are some of the applications of magnetic forces?

Magnetic forces have a wide range of applications in various fields such as electrical engineering, medicine, and transportation. Some examples include electric motors, MRI machines, and magnetic levitation trains.

## 4. Can magnetic forces be attractive or repulsive?

Yes, magnetic forces can be either attractive or repulsive depending on the direction of the charged particles or currents. If the particles or currents are moving in the same direction, the forces will be attractive. If they are moving in opposite directions, the forces will be repulsive.

## 5. How does distance affect the strength of magnetic forces?

The strength of magnetic forces decreases as the distance between the charged particles or currents and the magnetic field increases. This is because the magnetic field weakens as it spreads out, resulting in a weaker force acting on the particles or currents.

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