Help Experiment determining the Earth's magnetic field strength

[Timbo17]

I am in my senior year of school and I have been given a research task to do on the Earth's magnetic field in a given place. I have to come up with a full method for the experiment to perform in class in a week or so and then I need to use equations to create a discussion and show how I found the magnetic field using equations. My teacher has given me a pointers however. He said the experiment can be done using simply a compass, magnetic dip needle, power supply, connecting leads, resistors, ruler to measure distances and an ammeter to measure the current values. I have been researching to find methods and have found several but mostly they use equipment we don't have. So I could really use some help to create a method using the equipment listed above. Any ideas..?

 

[DrClaude]

Do you understand what you can produce with the equipment mentioned?

 

[Timbo17]

Not exactly?
I understand that by using the power supply and some of the other equipment that an electrical current will be produced creating a magnetic field around the system. I am not really sure though how this coincides with calculating the Earth's magnetic field in a given area?

 

[DrClaude]

I don't want to give too much away, but could you try to find a way to produce a magnetic field that is equivalent to Earth's?

 

[Timbo17]

So... Create a magnetic field using the equipment that balances the Earth's magnetic field, or cancels it in a sense. And if i do this then the field i have created is equal to that of the Earth's magnetic field and then i have the stength of the Earth's magnetic field? And i do this by using the dip needle and compass?

 

[Crazymechanic]

No Timbo17 you don't have to create anything everything is in fact already here.
Do you know how me measure the body weight? We step on a device that measures it and the device shows how strongly we push on the device.

Now the Earth's magnetic field is a static one at a given place.It's not time varying like the one you get from AC wires and so on.
Now you have a static field the compass turns till it stops showing the right coordinates , but what if you hold it with your finger while it is in it's way to the right coordinates? Then you feel some resistance from it because the magnetic field is trying to align it but you are holding it back.Now you won't feel anything much with your finger because the Earth's field is actually pretty weak.The stronger a given magnetic field the more force it will exert on the compass needle the harder it will be for you to hold it back from going to it's stopping position.

Now while the compass needle will go to it's position you can have a wire wound coil around it and then let it go while spinning to align itself with the magnetic field it will produce a current in the coil as a moving magnetic field induces a current in a conductor.Now the stronger the magnetic field will be the faster the needle will find it's position the larger the induced current will be.
Well this would be a very basic way of measuring the field strength with given some simple tools like a compass some wires etc.
Also you can make a coil near the needle and then run current from a battery through it and see at what voltage levels the needle changes it's position and then use that to approximate the field strength.
Professional instruments use the more fundamental properties of atoms to measure the field strength just in case your interested.

http://en.wikipedia.org/wiki/Magnetometer

 

[Timbo17]

Experiement to determine Earth's Magnetic field

Ok, so i have been given a compass, magnetic dip needle, power supply, resistors, an ammeter and connecting leads. I need to set up an experiment using this expiment to measure the Earth's magnetic field, any ideas?

 

[BobG]

Two ways: the way you mentioned or crazymechanic's way (measure the current created by the magnet's motion). Both ways work, but you also need to make some measurements.

Your way, measuring the strength of an electromagnet that holds the needle stationary when the needle is pointing perpendicular to the Earth's field, is probably going to be the easiest.

And the strength of the electromagnet will be measurable by the current required for the magnet.

 

[xAxis]

I don't think you can wind coil around compas needle because it's to small. And even if he manage to do that, there will be magnetic field generated around the coil, and it will interact with Earth's magnetic field.

 

[jtbell]

any ideas?

A straight current-carrying wire produces a magnetic field. Do you know how to calculate the field at distance r from such a wire, carrying a current I?

 

[davenn]

I don't think you can wind coil around compass needle because it's to small. ...

you are taking that a bit incorrectly ;)

The compass is placed within a coil

Dave

 

[BobG]

I don't think you can wind coil around compas needle because it's to small. And even if he manage to do that, there will be magnetic field generated around the coil, and it will interact with Earth's magnetic field.

you are taking that a bit incorrectly ;)

The compass is placed within a coil

Dave

It would probably work best if the compass needle were between the North Pole and your electromagnet instead of turning your compass into an electromagnet.