That a moving magnetic field produces an electric field and conversely that a moving electric field produces a magnetic field is part of the reason electric and magnetic forces are now considered as different manifestations of the same force first noticed by Albert Einstein. This classic unification of electric and magnetic forces into what is called the electromagnetic force is the inspiration for contemporary efforts to unify other basic forces.
Explain the relationship between the motional electromotive force, eddy currents, and magnetic damping. Motors and generators are very similar. Furthermore, motors and generators have the same construction. The motor thus acts as a generator whenever its coil rotates. This will happen whether the shaft is turned by an external input, like a belt drive, or by the action of the motor itself.
That is, when a motor is doing work and its shaft is turning, an EMF is generated. If motional EMF can cause a current loop in the conductor, we refer to that current as an eddy current.
Eddy currents can produce significant drag, called magnetic damping, on the motion involved. Consider the apparatus shown in, which swings a pendulum bob between the poles of a strong magnet. If the bob is metal, there is significant drag on the bob as it enters and leaves the field, quickly damping the motion. If, however, the bob is a slotted metal plate, as shown in b , there is a much smaller effect due to the magnet.
There is no discernible effect on a bob made of an insulator. Device for Exploring Eddy Currents and Magnetic Damping : A common physics demonstration device for exploring eddy currents and magnetic damping. In both cases, it experiences a force opposing its motion. Only the right-hand side of the current loop is in the field, so that there is an unopposed force on it to the left right hand rule.
When the metal plate is completely inside the field, there is no eddy current if the field is uniform, since the flux remains constant in this region. But when the plate leaves the field on the right, flux decreases, causing an eddy current in the clockwise direction that, again, experiences a force to the left, further slowing the motion. A similar analysis of what happens when the plate swings from the right toward the left shows that its motion is also damped when entering and leaving the field.
Conducting Plate Passing Between the Poles of a Magnet : A more detailed look at the conducting plate passing between the poles of a magnet. As it enters and leaves the field, the change in flux produces an eddy current. Magnetic force on the current loop opposes the motion. There is no current and no magnetic drag when the plate is completely inside the uniform field. When a slotted metal plate enters the field, as shown in, an EMF is induced by the change in flux, but it is less effective because the slots limit the size of the current loops.
Moreover, adjacent loops have currents in opposite directions, and their effects cancel. When an insulating material is used, the eddy current is extremely small, and so magnetic damping on insulators is negligible. If eddy currents are to be avoided in conductors, then they can be slotted or constructed of thin layers of conducting material separated by insulating sheets.
Eddy Currents Induced in a Slotted Metal Plate : Eddy currents induced in a slotted metal plate entering a magnetic field form small loops, and the forces on them tend to cancel, thereby making magnetic drag almost zero.
We learned the relationship between induced electromotive force EMF and magnetic flux. The number of turns of coil is included can be incorporated in the magnetic flux, so the factor is optional. In this Atom, we will learn about an alternative mathematical expression of the law. When the coils are stationary, no current is induced. But when the small coil is moved in or out of the large coil B , the magnetic flux through the large coil changes, inducing a current which is detected by the galvanometer G.
A device that can maintain a potential difference, despite the flow of current is a source of electromotive force. Electric generators convert mechanical energy to electrical energy; they induce an EMF by rotating a coil in a magnetic field. Electric generators are devices that convert mechanical energy to electrical energy.
They induce an electromotive force EMF by rotating a coil in a magnetic field. It is a device that converts mechanical energy to electrical energy. A generator forces electric charge usually carried by electrons to flow through an external electrical circuit.
Possible sources of mechanical energy include: a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air, or any other source of mechanical energy.
Steam Turbine Generator : A modern steam turbine generator. Consider the setup shown in. Charges in the wires of the loop experience the magnetic force because they are moving in a magnetic field. Charges in the vertical wires experience forces parallel to the wire, causing currents. However, those in the top and bottom segments feel a force perpendicular to the wire; this force does not cause a current. We can thus find the induced EMF by considering only the side wires.
Diagram of an Electric Generator : A generator with a single rectangular coil rotated at constant angular velocity in a uniform magnetic field produces an emf that varies sinusoidally in time.
Note the generator is similar to a motor, except the shaft is rotated to produce a current rather than the other way around. This expression is valid, but it does not give EMF as a function of time. Generators illustrated in this Atom look very much like the motors illustrated previously.
This is not coincidental. In fact, a motor becomes a generator when its shaft rotates. The basic principles of operation for a motor are the same as those for a generator, except that a motor converts electrical energy into mechanical energy motion. Read our atom on electric generators first.
Most electric motors use the interaction of magnetic fields and current-carrying conductors to generate force. Electric motors are found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives. If you were to place a moving charged particle in a magnetic field, it would experience a force called the Lorentz force:. Right-Hand Rule : Right-hand rule showing the direction of the Lorentz force.
Current in a conductor consists of moving charges. Therefore, a current-carrying coil in a magnetic field will also feel the Lorentz force.
For a straight current carrying wire that is not moving, the Lorentz force is:. The direction of the Lorentz force is perpendicular to both the direction of the flow of current and the magnetic field and can be found using the right-hand rule, shown in. Using your right hand, point your thumb in the direction of the current, and point your first finger in the direction of the magnetic field.
Your third finger will now be pointing in the direction of the force. Torque : The force on opposite sides of the coil will be in opposite directions because the charges are moving in opposite directions. This means the coil will rotate.
Both motors and generators can be explained in terms of a coil that rotates in a magnetic field. In a generator the coil is attached to an external circuit that is then turned.
This results in a changing flux, which induces an electromagnetic field. In a motor, a current-carrying coil in a magnetic field experiences a force on both sides of the coil, which creates a twisting force called a torque that makes it turn. Any coil carrying current can feel a force in a magnetic field. This force is the Lorentz force on the moving charges in the conductor.
The force on opposite sides of the coil will be in opposite directions because the charges are moving in opposite directions. Inductance is the property of a device that tells how effectively it induces an emf in another device or on itself. Induction is the process in which an emf is induced by changing magnetic flux. The answer is yes, and that physical quantity is called inductance. See, where simple coils induce emfs in one another.
Mutual Inductance in Coils : These coils can induce emfs in one another like an inefficient transformer. Their mutual inductance M indicates the effectiveness of the coupling between them. Here a change in current in coil 1 is seen to induce an emf in coil 2.
In the many cases where the geometry of the devices is fixed, flux is changed by varying current. A change in the current I 1 in one device, coil 1, induces an EMF 2 in the other. Consider a transformer of N 1 turns in the primary winding and N 2 turns in the secondary winding. When voltage V, applied to the transformer, emf E 1 induced in the primary winding will induce another emf E 2 in the secondary winding by mutual induction as shown below.
The frequency of the induced emf will equal the supply frequency f, and the magnitude of both fluxes due to magnetizing current I m will be the same as supply magnitude, i. As the input given to the transformer will be a sinusoidal waveform. From the emf equation of transformer, if E 1 and E 2 are the emf induced in the primary and secondary winding.
Then the ratio of there turns N 1 and N 2 in the primary and secondary winding is given as,. Your email address will not be published.
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