aim: how can we explain the 1 st two left hand rules of magnetism? do now: draw the magnetic field...

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Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing each other

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Page 1: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

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

Do Now:

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

Page 2: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

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/m2

– Symbol: T

Page 3: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

3 Dimensional Directions

Right Left Up Down Into Out of page page

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• • • • • • • • • • • • • • •

Page 4: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

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.

Page 5: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

Electromagnetism

• A wire carrying a current produces a magnetic field

• ‘Left-Hand Rules’ are used to determine the direction of magnetic fields

Page 6: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

1st 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

Page 7: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

Page 8: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

Page 9: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

x

x

x

x

x

x

x

x

x

x

Field coming into the page

Field coming out of the page

Current

Current

Page 10: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

2nd Left-hand Rule

• Curl left-hand fingers in direction of current on solenoid

• Thumb will point in direction of North Pole

Page 11: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

xxx

xx

x

xx x

x

Magnetic north is in the page

Page 12: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

• A number of loops coiled together

Solenoids

Page 13: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

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

Page 14: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

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

Page 15: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

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

Page 16: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

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

Page 17: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

Page 18: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

Page 19: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

+ + - -

Will these electromagnets attract or repel?

N NS S

Repel

Page 20: Aim: How can we explain the 1 st two left hand rules of magnetism? Do Now: Draw the magnetic field lines around two bar magnets with the north poles facing

x xxxxx

x xxxxx

e e

Magnetic fieldinto the page

Magnetic field out of page

Would these two wires attract or repel? Why?

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