Magnetic Fields

What do the magnetic field lines of a straight current carrying wire look like?

What do the magnetic field lines of a flat coil look like?

What do the magnetic fields lines of a solenoid look like?

How can you identify which pole a solenoid is?

What do the magnetic field lines look for two bar magnets attracting/repelling?

Fleming’s Left Hand Rule

• ThuMb = Motion

• First Finger = (Magnetic) field (N → S)

• SeCond finger = Current (+ → -)

What is the force experienced on a Current Carrying Conductor in a magnetic field equal to?

F = BILsinθ

B = Magnetic field strength

I = Current

L = Length

sinθ = angle it makes with the field lines

Tesla

• The unit where magnetic flux density is 1 tesla when a wire perpendicular to the field with a current of 1A experiences a force of 1N/m

• B = F/IL

Magnetic flux density

• A measure of how much magnetic flux is in an area

Magnetic flux

• Magnetic flux (Wb, weber= Magnetic flux density * area

Magnetic flux linkage

• Magnetic flux * number of turns on a coil

Galvanometer

• Used to measure extremely small currents

Electromagnetic induction

• “Cutting” field lines using a conductor, inducing a potential difference

Faraday’s Law

The magnitude of the induced EMF is directly proportional to the rate of change of magnetic flux linkage

• E = -ΔNϕ/Δt

Lenz’s Law

The direction of induced EMF always opposes the change that caused it

What is the difference between a motor and a generator?

• Motor takes electrical energy and outputs kinetic energy

• Generator takes kinetic energy and outputs electrical energy

Graph of magnetic flux against time in an AC generator

Sinoidal graph

Graph of EMF against time in an AC generator

Negative cosine graph (E = -dϕ/dt * N)

How can you increase the EMF producedby a generator?

• Increase magnetic field strength, area of coil, number of turns, speed of spin