# Where Am I Going Wrong in Calculating the Force Between Two Bar Magnets?

• Mutaja
In summary, the conversation discusses the computation of the force between two bar magnets with a copper gap of 1mm thickness. The formula used is F = B∂ * H∂ * A∂, and the necessary values for B and H are calculated. The area is corrected from 2.5cm2 to 0.00025m2 and the equation is adjusted to include 1/2. The resulting force is 24.87N. The conversation also addresses the issue of inconsistent units and the importance of accuracy in calculations.
Mutaja

## Homework Statement

You're given two bar magnets as shown below. In the gap between the two bar magnets, there's a bit of copper that's 1mm thick. The area of the bar magnet is 2.5cm2, and the flux density is 0.5T. Compute the force between the two bar magnets.

## The Attempt at a Solution

So the force is given by this formula:

F = B * H * A

H = $\frac{B}{µ0}$ = $\frac{0.5T}{4∏ * 10^-7}$ = 397887

F = 0.5T * 397887 * ##2.5cm^2## = 497385.

The answer I get is about 20 000 times bigger than what I'm expecting.

Where am I going wrong?

F is the force.
B is the flux density in the air gap.
H is the field strength in the air gap.
A is the area in the air gap.

I'm sorry for the use of the wrong symbol, but ∂ was the closest I could get.

Also, I realized that I have a gap filled with copper instead of air, just as I was about to post this. I have no examples involving gaps with anything else than air as far as I'm aware. I will keep looking for this and update this post if I find anything.

Any input is appreciated.

#### Attachments

• bar magnets.PNG
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Well, for one thing, you are sloppy and inconsistent with the units of your calculation. Is area supposed to be in cm^2 or m^2? It makes a difference.

SteamKing said:
Well, for one thing, you are sloppy and inconsistent with the units of your calculation. Is area supposed to be in cm^2 or m^2? It makes a difference.

I'm sorry for this. 2.5cm2 should be 0.00025m2.

Also, I've overlooked the fact that my equation should contain 1/2.

I therefore get 24.87N, and that looks alright.

Thanks for your input, even if it's just to let me know I'm not doing my work properly.

## 1. What is the force between two bar magnets?

The force between two bar magnets is the attractive or repulsive force that exists between them due to their magnetic fields. This force is strongest when the magnets are placed close to each other, and it decreases as the distance between them increases.

## 2. How does the placement of the bar magnets affect the force between them?

The force between two bar magnets depends on their relative positions. If the magnets are placed with their opposite poles facing each other, they will experience an attractive force. However, if their like poles face each other, they will experience a repulsive force.

## 3. What factors affect the strength of the force between two bar magnets?

The strength of the force between two bar magnets depends on the strength of the magnetic field of each magnet, the distance between them, and the orientation of their poles. The stronger the magnetic fields and the closer the magnets are, the stronger the force will be.

## 4. Can the force between two bar magnets be increased?

Yes, the force between two bar magnets can be increased by increasing the strength of their magnetic fields or by decreasing the distance between them. This can be achieved by using stronger magnets or by bringing the magnets closer together.

## 5. How is the force between two bar magnets calculated?

The force between two bar magnets can be calculated using the inverse square law of magnetism, which states that the force is inversely proportional to the square of the distance between the magnets. This means that as the distance between the magnets decreases, the force between them increases exponentially.

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