Magnetism Alternating-Current Circuits

Alternating Current Generators

Alternating current motor

A coil of area A and N turns rotating with constant angular velocity in a uniform magnetic field produce a sinusoidal emf

Instead of mechanically rotating, we can apply an ac potential difference generated by other ac generator to the coil. This produces an ac current in the coil, and the magnetic field exerts forces on the wires producing a torque that rotaes the coil.

The magnetic field.

Magnetic forces on a moving charges.

Magnetic forces on a current element

Torques on current loops and magnets

The Magnetic FieldMagnets

The Earth is a natural magnet with magnetic poles near the north and south geographic poles.

The Magnetic Field

Magnets Does exist an isolated magnetic pole?

The SI units of magnetic field is the tesla [T]

Earth magnetic field is about 10-4 T

Powerful laboratory produce fields of 1 -2 T as maximum

1 Gauss [G] = 10-4 Tesla [T]

The Magnetic Field

The Magnetic Field. Magnetic force on a moving charge

A proton is moving in a region of crossed fields E = 2x105 N/C and B = 3000 G, as is showed in the figure. (a) What is the speed of the proton if it is no deflected. (b) If the electric field is disconnected, draw the path of the proton

The Magnetic Field. Magnetic force on a current element

In the case of a straight segment of length L

The Magnetic Field. Torques on Current loops and Magnets

A circular loop of radius 2 cm has 10 turns of wire and carries a current of 3 A. The axis of the loop makes an angle of 30º with a magnetic field of 8000 G. Find the magnitude of the torque on the loop.

BA current-carrying loop experiences no net force in a uniforme magnetic field, but it does experience a torque that tends to twist the loop

Sources of Magnetic Field

The Magnetic Field of Moving Charges

The Magnetic Field of Currents. The Biot-Savart Law

The Magnetic Field Due to a Current loop

Sources of Magnetic Field

Moving Point Charges are the source of Magnetic Field

Sources of Magnetic Field

A solenoid is a wire tightly wounded into a helix of closely space turns . A solenoid is used to produce a strong, unifrom magnetic field in the region surrounded by the loops

Inside a long solenoid

Find the magnetic field at the center of a solenoid of 600 turns that carries a current of 4 A

Sources of Magnetic Field: Solenoid and magnets

Left: Magnetic field lines of a solenoid; right Magnetic field lines of a bar magnet

Magnetic Induction

Magnetic Flux

Induced EMF and Faraday´s Law

Lenz´s Law

The induced emf is in such direction as to oppose, or tend to oppose, the change that produces it. Lenz´s Law

MAGNETIC INDUCTION

Alternating Current Generators

Alternating current motor

A coil of area A and N turns rotating with constant angular velocity in a uniform magnetic field produce a sinusoidal emf

Instead of mechanically rotating, we can apply an ac potential difference generated by other ac generator to the coil. This produces an ac current in the coil, and the magnetic field exerts forces on the wires producing a torque that rotaes the coil.

29-2Alternating Current in a Resistor

29-3Alternating Current Circuits

29-4Phasors

29-5LC and RLC Circuits Without

a Generator

29-6Driven RLC Circuits

29-7The Transformer

Problems