why a conductor does not produce e.m.f when rotated in earths magnetic field?

Question

we do not have terminal emf for a conductor rotated in earth magnetic field. why?

Answer 1

It does, but the Earth's magnetic field strength is very weak so the resulting emf is too small to be noticed.

The strength of the field at the Earth's surface ranges from less than 30 microteslas (0.3 gauss) in an area including most of South America and South Africa to over 60 microteslas (0.6 gauss) around the magnetic poles in northern Canada and south of Australia, and in part of Siberia.

So let's assume that we have a simple setup that can induce an EMF from Earth's magnetic field:

EMF = -dΦ/dt, where Φ is the magnetic flux

If we consider a very simple case where Φ = BA, where B is the magnetic field and A is the surface area. So let's assume that

B = 60 microTesla = 60 x 10^-6 Tesla or 0.00006 T
A = 1 square meters

and let the time duration of the manetic flux change be = 1 sec

Then EMF = |-dΦ/dt| = BA/t = (0.00006)(1)/(1) = 0.00006 Volts

As you can see, I had to let the area of the magnetic flux be rather large (1 square meters). To see any sizable effect, we would actually need to consider much much bigger area, maybe like a square kilometer.

Answer 2

EMF needs 3 things 1 a conductor
2 motion
3 a magnetic field

the earth displaces (negates magntic fields) that is why you need to induce EMF with a magnet.

Answer 3

1. It has to rotate -across- the field (like at a 90 degree angle)

2. Earth's magnetic field is VERY weak, unless the conductor was huge, it wouldn't be enough to measure

Answer 4

been a while since I learned physics... there are some conditions. conductor needs to for form a closed loop, there is no change in the magnetic field, the field must have some perpendicular component with relation to the loop. Or the magnetic field is too small to be measured.

Answer 5

Yes. In fact I remember a demonstration of this in my school physics class. It was a big coil that you could rotate very quickly. This has been proposed and tested as a means of generating power in space, if you have a long wire strung between two satellites, it will generate an electric current as it cuts through the earth's magnetic field. The return path for the current is through space, which conducts electricity quite well because of the ions in it (in the vicinity of the earth at least).

Answer 6

Indeed, we do! It is simply that the earth's magnetic field is so weak that it is difficult to detect the e.m.f. so generated.

Answer 7

the magnetic field of the earth is weak.. ok .