# Currents and magnetic fields in a coil

• -_-'
In summary: There is a force on the bottom of the coil and a force on the top. The top force is greater because it is acting at a greater distance from the center of the magnet. So the magnitude of the magnetic force is 9.8 N. In summary, the magnetic field strength of a horseshoe magnet is 9.8 N.
-_-'

question: Use the following quantities to calculate the magnetic field strength of the horseshoe magnet.

Mass of coil: 20 grams
current in coil: 2.0 amps
length of bottom of coil: 10cm
angle coil makes with vertical: 30 degrees

Hint: Equate magnetic force on bottom of coil to the horizontal componen of the coils weight.

I've got a diagram
http://i122.photobucket.com/albums/o272/science_f/0000000000000coilandmagnet.jpg

I don't know where to start in the calculating process Can someone please help me with the starting point and i'll try and progress from there...this is the first time I've seen a problem like this

these are the formulas I know:
B=F/IL
F=BIL sin @
B=kI/r
B=2(pi)knI

Where k is Amperes constant (2x10^-7NA^-2), L is the length of wire, I is the current, r is the radius of the wire (but in some cases the distance between wires), and F is the force.

Here's another diagram with brainstorming but I'm not sure if i grasp the concept of this...I think it is all wrong

http://i122.photobucket.com/albums/o272/science_f/000000000000h.jpg

I actually think that there isn't enough information to do the problem unless it is as simple as:
F=mg=20x9.8=196
B=F/IL
B= 196/2.0x10
B=9.8
But i don't think that can be right

Last edited:
-_-' said:

question: Use the following quantities to calculate the magnetic field strength of the horseshoe magnet.

Mass of coil: 20 grams
current in coil: 2.0 amps
length of bottom of coil: 10cm
angle coil makes with vertical: 30 degrees

Hint: Equate magnetic force on bottom of coil to the horizontal componen of the coils weight.

I've got a diagram
http://i122.photobucket.com/albums/o272/science_f/0000000000000coilandmagnet.jpg

I don't know where to start in the calculating process Can someone please help me with the starting point and i'll try and progress from there...this is the first time I've seen a problem like this
What is a horizontal component of weight? I don't think they really mean that. The magnet will exert a force on the lower branch of the coil. You need to think about the direction of the magnetic force. You also need to think about what is keeping the coil in position. There has to be something besides the magnetic force. Something has to be keeping the top of the coil in position. What will be the direction and magnitude of the force on the top of the coil? It will help if you rotate the image so that the magnet is in the plane of the page, and the loop is perpendicular to the page so that the 30 degree tilt can be seen.

Last edited:
thanks for that every little bit of info helps

-_-' said:
thanks for that every little bit of info helps
Hopefully you will recognize that this becomes a statics problem where one of the forces involved is a magnetic force. Think forces and torques and all the usual things you use for statics problems.

## 1. What is the relationship between the direction of current and the direction of magnetic field in a coil?

The direction of current in a coil determines the direction of the magnetic field produced by the coil. The magnetic field lines around the coil are perpendicular to the direction of current flow.

## 2. How does the number of turns in a coil affect the strength of the magnetic field?

The more turns there are in a coil, the stronger the magnetic field will be. This is because each turn of the coil contributes to the overall magnetic field, and the more turns there are, the more magnetic field lines are produced.

## 3. What is the difference between an electromagnet and a permanent magnet?

An electromagnet is created by passing an electric current through a coil, while a permanent magnet is made of a material that naturally has a magnetic field. Electromagnets can be turned on and off by controlling the current flow, while permanent magnets have a constant magnetic field.

## 4. How does the shape of a coil affect the magnetic field it produces?

The shape of a coil can affect the strength and direction of the magnetic field it produces. For example, a tightly wound coil will have a stronger magnetic field than a loosely wound coil with the same number of turns. The shape of the coil also determines the direction of the magnetic field lines.

## 5. What is the significance of the direction of the magnetic field in a coil?

The direction of the magnetic field in a coil is important because it determines how the coil will interact with other magnetic fields. If the magnetic field in the coil is in the same direction as an external magnetic field, the two fields will reinforce each other, while opposite directions will cause them to cancel each other out.

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