# Magnetisim

Magnetisim

Magnetic field: Any region of space where magnetic force can be felt.

Magnetic field line: A line drawn in a magnetic field so that the tangent to it shows the direction of the field.

Show 1. Magnetic field lines = paper and iron fillings

2. Magnetic field = compass (deflects in magnetic field).

3. Plot of magnetic field in conductor = Thread card onto wire and use compass to plot the field.

Right hand grip rule: The right hand clasps a conductor with the thumb pointing in the direction of the current (ie. From positive to negative) then the fingers give the direction of the magnetic field.

Electro magnet: Soft iron core inside a solenoid with current passing through it. No current no magnetism.

Current in a magnetic field experiences a force which is perpendicular to the field.

Shown by: Strip of tin foil connected to a battery. Tin foil placed between the poles of a U magnet.

Magnetic forces between 2 current carrying conductors = Shown by: A loop of tinfoil connected at one end to the positive of a battery and at the other to the negative. The side of the loop will be attracted to each other.

Fleming's left hand rule: Thumb = Force, Index finger = magnetic field, Middle finger = Current. (FBI).

Magnetic flux density (B) = A Vector force with magnitude one Tesla when all else in F = BIL is also one.

If an electron enters a magnetic field it will move in a circle following Fleming's left hand law.

Electromagnetic Induction = A changing magnetic field in a coil produces an emf.

Faraday's Law = The size of the emf produced is directly proportional to the rate of change of flux.

Lenz's Law = The direction of the induced emf opposes the force producing it.

All the above are shown using a coil, magnet and galvanometer.

Electric generator = Device converting me chemical to electrical energy.

Mutual induction = Where a changing magnetic field in one coil causes an emf to appear in another nearby coil. (Induced emf will increase if: coils are close together, on the same iron core, have more turns)

Self Induction = Where a changing magnetic field causes a back emf in itself, which opposes the main flow of current through the coil. Shown by: Coil on iron core, battery, bulb. Close switch bulb takes a second to light.

Rms values. Value given to AC's DC equivalent. Eg: 5A rms in AC has the same effect as 5A DC..

A charged capacitor will not allow DC to flow but it will allow AC to flow.

Transformer:Device which can change the value of an alternating voltage.

Use two voltmeters to show this action. One measures input voltage and the other output voltage.