Physics

Eddy current👼

An eddy current is a closed loop current that flows in a conductor. By Lenz's law the direction of that induced emf opposes the emf causing the motion of the armature. The current generated in the motor is an eddy current. The direction of the motor eddy current is such that it opposes the supply emf that produces the motion in the motor. The net emf applied to the coils equals the supply emf minus the back emf.

Lenz's Law🙏

Electric motors use an external emf applied to the coils to produce an electtric current in the coils positioned in an external magnetic field. This current produces a magnetic field that interacts with the external magnetic field. As the coils rotate in the external magnetic field, an emf is induced in the coils due to the constantly changing magnetic flux threading the coils. By Lenz's Law, this induced emf is in the opposite direction to the external supply emf causing the rotation, and it has the effect of reducing the net emf applied to the coils. Because the induced emf is in the opposite direction to the supply emf, it is known as the back emf.

Define magnetic field strength B as magnetic flux density

Magnetic flux density is a measure of the number of magnetic flux lines passing through a unit area (one metre squared) Magnetic field strength B at a point is defined to be the same as magnetic flux density.

Faraday's Law of electromagnetic induction🌑🌒🌓🌔🌕🌖🌗🌘🌚

Quantitatively, the potential difference or emf Epsilon induced in a conductor is the amount of flux cut Delta Phi divided by the time taken.

Lenz's law follows from the Law of Conservation of Energy👉👈

That law says energy cannot be created nor destroyed but can simply change form. In the case of the magnet and coil, energy must be transferred to the coil to produce the induced current flow (electrical energy). That energy is the work done in inserting the coil or withdrawing it. It is therefore necessary that work must be done against the magnet moving relative to the coil if it is to generate the emf in the coil. If it were not so, the induced magnetic field would accelerate the magnet, thus increasing the induced emf which, in turn would increase the strength of the induced field, further accelerating the magnet, and so on, contravening the Law of Conservation of Energy.

Magnetic flux In SI units, magnetic flux is measured in Webers (Wb) and magnetic flux density is measured in Webers per square metre (Wb m-2)

The amount of magnetic field threading or "flowing through" a certain area A, such as the area inside a flat coil of wire. flux = flux density × area

Why is back emf needed?👾👾👾

The back emf increases as the speed of the motor increases, until the net emf is just sufficient to provide the energy for the work the motor is doing, against its own internal friction and any load that is applied to it. If there were no back emf, the motor would continue to spin faster and faster indefinitely.

Back emf👾

The emf induced in the coils of a motor as they spin in the external magnetic field of the stator.

Rotor👦

The rotating part of an electrical rotating machine.-coils

Stator👨

The stationary part of an electrical rotating machine. -the sections that produce the magnetic fields (permanent magnets or electrical magnets)

Describe generated potential difference as the rate of change of magnetic flux through a circuit.😳

Whenever there is relative motion between a conductor in a circuit and a magnetic field, the circuit cuts the magnetic flux. It causes an increase in the current flowing in the circuit and therefore the potential difference. Thus the generated potential difference increases as the rate of change of flux in the circuit increases.

When a greater load is applied to the motor, the armature rotates😧---- and the back emf is---- 😾😿This allows a ----current to flow through the coils, resulting in an ----😬torque to match the extra load.

more slowly reduced greater increased

Define the rate of change of flux in the circuit. Quantitatively describe it.👶. What law is this?

👸The generated potential difference is called ---electromotive force (emf). 🌖The emf induced in a conductor is the amount of flux cut divided by the time taken. 🐼It is faraday's law of electromagnetic induction.

Four methods to increase the rate at which the flux is cut or emf.

💜decreasing the distance between the conductor and the magnetic field. 💛increasing the strength of the magnet. 💚increasing the speed of the relative motion between the conductor and the magnetic field. 💙increasing the angle between the direction of motion of the conductor and the direction of the magnetic field from near 0 towards 90 degrees.