- #1
ellieee
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why does the current reverse when the coil is at this position in A.C generator ?
A.C. generator -> why does the current reverse?
In summary, the direction of the current in an A.C generator reverses when the coil is at a certain position because of the change in the number of field lines and the Lorentz force. This can also be explained by Lenz's law, where the current runs in a direction to oppose the change in magnetic flux. This results in a reversal of the current direction in the top wire, ensuring that the current always flows in a direction to reduce the flux lines through the loop.
why does the current reverse when the coil is at this position in A.C generator ?
- #2
BvU
Science Advisor
Homework Helper
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Because the number of field lines (the magnetic flux) moves away from a maximum (or towards it, depending on which way it's rotating).
So the time derivative changed sign (or will change, depending on which way it's rotating) .
A better way to look at this is to use the Lorentz force: The velocity with which the pink and blue conductors move through the B field changes sign.
##\ ##
So the time derivative changed sign (or will change, depending on which way it's rotating) .
A better way to look at this is to use the Lorentz force: The velocity with which the pink and blue conductors move through the B field changes sign.
##\ ##
- #3
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Here is an alternate explanation in terms of Lenz's law.
According to Lenz's law, the induced current will run in a direction that will oppose the proposed change in magnetic flux. Look at the picture. The direction of the current is such that it tends to reduce the flux lines through the loop. This means that the proposed change is to increase the field lines through the loop. For that to happen, the loop must be turning counterclockwise.
Having established the sense of rotation, note that the current in the top (pink) wire is into the screen. After the loop has rotated by 180o, the current in the top wire must be into the screen for the same reasons as before. But the top wire now is the blue wire. If the current in the blue wire did not reverse direction somewhere in between (specifically when the field lines are in the plane of the loop), the current in the top wire would be out of the loop and that would violate Lenz's law.
According to Lenz's law, the induced current will run in a direction that will oppose the proposed change in magnetic flux. Look at the picture. The direction of the current is such that it tends to reduce the flux lines through the loop. This means that the proposed change is to increase the field lines through the loop. For that to happen, the loop must be turning counterclockwise.
Having established the sense of rotation, note that the current in the top (pink) wire is into the screen. After the loop has rotated by 180o, the current in the top wire must be into the screen for the same reasons as before. But the top wire now is the blue wire. If the current in the blue wire did not reverse direction somewhere in between (specifically when the field lines are in the plane of the loop), the current in the top wire would be out of the loop and that would violate Lenz's law.
FAQ: A.C. generator -> why does the current reverse?
Why does an A.C. generator produce alternating current?
An A.C. generator produces alternating current because it uses a rotating magnetic field to induce a current in the stationary coils of wire. As the magnetic field rotates, it causes the direction of the current to reverse, resulting in an alternating current.
How does the direction of the current reverse in an A.C. generator?
The direction of the current in an A.C. generator reverses due to the principle of electromagnetic induction. As the magnetic field rotates, it creates a changing magnetic flux through the coils of wire, which in turn induces a current in the opposite direction.
What causes the magnetic field to rotate in an A.C. generator?
The magnetic field in an A.C. generator is created by the rotation of the rotor, which is typically a set of magnets or electromagnets. As the rotor spins, it creates a rotating magnetic field, which is essential for the generation of alternating current.
Why is alternating current preferred over direct current in certain applications?
Alternating current is preferred over direct current in certain applications because it can be easily transformed into different voltages using a transformer. This makes it more suitable for long-distance power transmission and distribution. Additionally, alternating current can be easily converted to direct current using a rectifier, making it versatile for different types of devices and equipment.
Can an A.C. generator also produce direct current?
Yes, an A.C. generator can also produce direct current by using a commutator, which is a mechanical switch that changes the direction of the current as the rotor rotates. This type of generator is known as a dynamo and was commonly used before the development of modern rectifiers.