Electricity from Magnetism - (Physics 3)

Inducing a current in a circuit

Can be done without a battery or an electrical power supply

Electromagnetic induction

The process of inducing a current in a circuit by changing the magnetic field that passes through the circuit

Electromagnetic induction example

When a circuit loop crosses the lines of the magnetic field, a current is induced in the circuit as indicated by the movement of the galvanometer needle

Dependence of the polarity of the induced emf

The direction in which the wire is moved through the magnetic field

Magnitude of the induced emf and current

Depends partly on how the loop is oriented to the magnetic field

Magnetic field is perpendicular to…

Both the plane and the motion of the loop exerts a magnetic force on the charges in loop

If the area of the loop is moved parallel to the magnetic field…

There is no magnetic field component perpendicular to the plane of the loop (no induced emf to move the charges around the circuit)

Ways of inducing a current in a circuit

Circuit is moved into or out of the magnetic field

Circuit is rotated in the magnetic field (angle between area of the circuit and magnetic field changes)

Intensity and/or direction of magnetic field is varied

As a magnet approaches a coil,

The magnetic field passing through the coil increases in strength

Bar magnet moving away from a coil

The induced magnetic field is similar to the field of the bar magnet

Lenz’s law

The magnetic field of the induced current is in a direction to produce a field that opposes the change causing it

Faraday’s law of magnetic induction

How a changing magnetic field can induce an electric current in a circuit

Faraday’s law of magnetic induction equation

emf = -N(△Φ_M/△t)

-N symbol

Negative number of loops in the circuit

(△Φ_M/△t)

The time rate of change of the magnetic flux