Aim: How can we explain the 1 st left hand rules of magnetism?

two Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing each other

Units for Magnetism •

Weber

: amount of magnetic flux (how many field lines are passing through a surface) – Symbol: Wb • Tesla: magnetic flux density (number of field lines per unit of area, Strength of B field) – Units: Wb/m 2 – Symbol: T

Right 3 Dimensional Directions Left Up Down xxxxx xxxxx xxxxx Into page • • • • • • • • • • • • • • • Out of page

In April of 1820, Danish physicist Hans Ørsted made a surprising observation while setting up for a lecture he was giving. He noticed that the compass needle was deflected from magnetic north when the electric current from the battery he was using was switched on and off.

He later went on to proved that a current carrying wire produces a magnetic field - and this makes sense, because it is the non-symmetrical movement of electrons.

Electromagnetism

• A wire carrying a current produces a magnetic field • ‘Left-Hand Rules’ are used to determine the direction of magnetic fields

1

st

Left-Hand Rule

• Used for determining the magnetic field in a straight wire • Grab the wire so your thumb points in the direction of the current flow - your curved fingers point in the direction of the magnetic field

Field coming into the page Field coming out of the page Current

x x x x x x x x x x

Current

2

nd

Left-hand Rule

• Curl left-hand fingers in direction of current on solenoid • Thumb will point in direction of North Pole

x x x x x x x x x x

Magnetic north is in the page

Solenoids • A number of loops coiled together

Electromagnets

• Strength of solenoid can be increased by: (1)Inserting a ferromagnetic material (e.g. iron) into center of coil (electromagnet) (2)Increasing the current in the coil (3)Increasing the number of turns of coil

The higher the magnetic permeability, the stronger the magnetic field.

The amount of current in a coil directly relates to magnetic field strength

The number of turns of wire directly relate to the strength of the magnetic field.

N Will these electromagnets attract or repel?

N + S S +

Repel

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Magnetic field into the page x x x x x x e  Magnetic field out of page Would these two wires attract or repel? Why?

e  x x x x x x