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can we generate electricity from earth magnetic field? As we know that earth behaves like magnet having two poles ..and according two Faraday law changing magnetic flilux causes emf ...what if I roate a coil in earth magnetic field ?

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closed as off-topic by Dmitry Grigoryev, winny, Maple, Voltage Spike, Sparky256 Aug 30 '18 at 22:33

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  • \$\begingroup\$ According to Faraday: yes. But is it practical? \$\endgroup\$ – Long Pham Aug 29 '18 at 14:48
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    \$\begingroup\$ It's an interesting question if you didn't know the answer to it but it's not a good source of energy... Otherwise, you'd see it more often in our society. The downvotes are likely due to uncertainty of trying to generate a massive of amount of "free" energy. \$\endgroup\$ – KingDuken Aug 29 '18 at 15:32
  • \$\begingroup\$ See "fluxgate compass principle". Coil is adjusted to no output, a deviation from curse will deflect an dc indicator one way or another. \$\endgroup\$ – Optionparty Aug 30 '18 at 2:50
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    \$\begingroup\$ I'm voting to close this question as off-topic because I believe such questions should be posted on Physics.SE. This site is about engineering. \$\endgroup\$ – Dmitry Grigoryev Aug 30 '18 at 11:14
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Yes, a properly-oriented rotating coil in a static magnetic field can generate electrical power.

That power comes from the mechanical power put into the system by rotating the coil. The power does NOT come from the magnetic field. If you were thinking this is some kind of free energy solution, then go back to high school physics.

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  • \$\begingroup\$ At these "power" levels, it might be usable as some kind of sensor. \$\endgroup\$ – gbarry Aug 29 '18 at 15:15
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Yes. Faraday’s law states:

emf = -dphi_B/dt

The strength of the earth’s magnetic field is approximately 25 microtesla. Let’s assume the coil has an area of 1m^2 and is rotating at 6000 RPM, or 100 revolutions per second. Then dphi_B/dt = d/dt 25 uT * 1m^2 * sin(100 * 2pi * t) = 16 mV * sin(100* 2pi * t), i.e. 16 millivolts 100hz AC. Maximum power is generated when the current in the coil generates an opposing flux of half the original.

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Yes you can. The theory is described in other answers and the initial experiment was done in 1996.

The space tether experiment called for a large, spherical satellite-to be deployed from the US space shuttle at the end of a conducting cable (tether) 20 km long. The idea was to let the shuttle drag the tether across the Earth's magnetic field, producing one part of a dynamo circuit. The return current, from the shuttle to the payload, would flow in the Earth's ionosphere, which also conducted electricity, even though not as well as the wire.

See https://www.space.com/521-electrodynamic-tethers-swing.html, https://en.wikipedia.org/wiki/STS-75 and there is even a video https://www.youtube.com/watch?v=As-wYmFYb3I

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