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The Alternating Current Generator
According to Faraday's law of electromagnetic induction, when there is a change in the magnetic flux Φ through a circuit (coil), an induced emf appears depending on the rate of change of magnetic flux:
εind = ΔΦ/Δt.
The magnetic flux Φ through the area S equals, by definition,
Φ = B?S?cosα,
Where B is the magnitude of the magnetic field, and α is the angle between B and the normal to the plane of the circuit.
If a rectangular frame with area S rotates at uniform angular velocity making f turns per second in a uniform magnetic field B, the magnetic flux through the frame is a periodic function of time:
Φ(t) = B?S?cos()2πft.
Thus, a periodic voltage that equals
εind = 2πfBSsin(2πft)
Appears between the ends of the frame. The amplitude of this voltage is proportional to the angular velocity of the frame. This frame is a model of an alternating current generator. If the terminals of the frame are connected to a special collector device, a direct current generator is created.
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