Unit 5 : Magnetism and Electromagnetic Induction

The space surrounding a magnet is called a magnetic field.

• We use (x) when the magnetic field goes into the plane.

• We use (.) when the magnetic field goes out of the plane.

A permanent bar magnet creates a magnetic field that closely resembles the magnetic field produced by a circular loop of current-carrying wire.

$F = qv x B$ with magnitude: $F = qv B \sin{\theta}$

• F = force

• q = charge

• v = velocity

• B = magnetic field

Whenever you use the right-hand rule, follow these steps:

• Orient your hand so that your thumb points in the direction of the velocity v.

• If the charge is negative, turn your thumb by 180 degrees.

• Point your fingers in the direction of B.

• The direction of FB will then be perpendicular to your palm.

$F = ILB$ with magnitude: $F = BIL \sin{\theta}$

• F = force

• B = magnetic field

• I = current

• L = length of conductor

$B= \frac{\mu_o I}{2\pi r}$

• B = magnetic field

• I = applied current

• μo = permeability of free space

• r = the distance from the wire where the magnetic field is calculated

The induced current will always flow in the direction that opposes the change in magnetic flux that produced it.

$Emf = -N \frac{\Delta \Theta}{\Delta t}$

• ‘Emf’ = Induced voltage or electromotive force.

• ‘N’ = The number of loops.

• ‘Δϕ’ = Change within magnetic flux.

• ‘Δt’ = Change in time

Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced. If the conductor circuit is closed, a current is induced, which is called induced current.

The induced emf in a coil is equal to the rate of change of flux linkage.

$Emf = - \frac{\Delta \Theta}{\Delta t}$

• emf = electromotive force

• dΦ = change in magnetic flux

• dt = change in time

It is created in three ways:

• Changing the area of the loop of wire in a stationary magnetic field.

• Changing the magnetic field strength through a stationary circuit.

• Changing the angle between the magnetic field and the wire loop.

Motional emf is the electromotive force generated by the motion of a conductor through a magnetic field.

It is given by the equation emf = Blv, where

• B is the magnetic field strength

• l is the length of the conductor

• v is the velocity of the conductor

This phenomenon is used in various applications, such as electric generators and motors.

Solenoid is a device that is constructed by a series of coaxial wires through which a continuous current flow.

mutual induction

increase in strength

a magnetic field

a voltage is generated in that conductor

Any material that is attracted to a magnet and has magnetic domains.

A place on the magnet where the force of attraction is greatest.

a) like poles repel each other

b) unlike poles attract each other

From the north pole to the south pole.

Device that uses current flow through conductors around a core to create magnetism.

The total lines of force surrounding a magnetic material. The symbol is Φ.

The ability of a material to concentrate flux as compared to air. The symbol is μ.

a) The amount of current through the coil

b) The number of turns on the coil

c) The core material

a) flux density

b) the number of turns in a conductor

c) The rate at which lines of force are cut by the conductor which is determined by the velocity and the angle of cut

Mutual induction takes place when a change in current and one circuit causes a voltage to be induced into another separate circuit.

a) ignition coils

b) transformers

L, henry, H