What current is needed in the solenoid's wires?

Question

A researcher would like to perform an experiment in a zero magnetic field, which means that the field of the earth must be cancelled. Suppose the experiment is done inside a solenoid of diameter 1.5m, length 3.0m, with a total of 8000 turns of wire. The solenoid is oriented to produce a field that opposes and exactly cancels the field of the earth.

What current is needed in the solenoid's wires?

Answer 1

An the thickness of the wire?

Are these single or overlapped wires?

Are there gaps between the wires?

Why not just put a compass in the tube and increase the current until the compass drifts from North?

The strength of the earth's magnetic field is not the same everywhere rmember. Your question amounts to 'How long is a piece of string?'

Answer 2

There is no way to answer this without further specific detail, such as the voltage, wire resistance per unit length, physical shape of the core, whether there even IS a core, what the material of the core is made from, the strength of the Earth's field at the location of the coil. The magnetic field of the Earth is constantly changing, so how will you account for this constantly changing field strength? The only way would be to experimentally determine the current by making this coil and then using a magnetometer and adjusting the current flow until the magnetometer stopped working. A magnetometer is so sensitive that even something as small as a car 50 feet away will disrupt the magnetic field enough to see a response. You can make a magnetometer easily with a strand of dental floss, a small mirror and a small rare earth magnet. Glue the magnet to the bottom of the mirror. Split the dental floss into the smallest strands you can. Use this thread to suspend the magnet/mirror assembly. Use a clear plastic cover to prevent air currents from moving the mirror. Use a focused beam of light and shine it on the mirror at an angle so the beam reflects to a wall several feet away. The longer the path from the mirror to the wall, the more sensitive the device. Mark the spot after the mirror stabilizes and stops moving, which means it is aligned with the field. Now, as the field changes, the mirror will move slightly to stay aligned. You will see the spot of light move as the field changes, through regular cycles. There is a daily cycle because of our rotation about our axis so sometime during the day, you face the Sun and the magnetic field of the Earth is affected by that, and is not affected so much at night  There is a monthly cycle based on the position of the moon relative to the Earth and Sun. There is also a yearly cycle because of the tilt of the axis relative to the magnetic field of the Sun and because our orbit is elliptical and not circular. Once you account for all of the various regular cycles, only THEN can you use your coil to negate the field exactly, and then, it will be for only a few moments until your constant strength field reacts to the constantly changing field of the Earth. I have a working magnetometer in my living room. I use it to determine if the conditions are right to see an aurora. At 48 degrees north latitude, I can see the upper atmosphere above the north pole where an aurora is most likely to happen in the northern hemisphere. Particles from solar flares impinging on the atmosphere disrupt the magnetic field and when the field changes out of the regular cycles, it is possibly for an aurora because of ionized particles from the sun which means going outside and looking up and north. There is no way for me to give you a number which answers this question. From what you have given, the only way to determine the answer is by actually doing the experiment.