P6 (L1)

MAGNET- a material that produces a magnetic field

• Comes in various shapes, sizes, and strengths

Facts about MAGNETISM:

1. Have 2 poles (North and South); always occur in pairs

2. Opposites attract, like poles repel

3. Magnets create a MAGNETIC FIELD around them

MAGNETIC FIELD

• Also called B-Field– “B” is the symbol for Magnetic Field with Tesla (T) as the unit

• A magnetic field is 3d in nature; represented by lines LEAVING north and ENTERING south

• Invisible but responsible for the most notable property of a magnet

• a force that pulls on other ferromagnetic materials (like iron, steel, nickel, cobalt)

HISTORY OF MAGNETS

• People have been aware of magnets and magnetism for thousands of years particularly in a region of Asia Minor called Magnesia.

Earth’s Magnetic Pole

• The geographic North Pole is a magnetic South Pole (inverse)

Earth’s Magnetic Field

• Aka geomagnetic field– a b-field that extends from the Earth's interior out into space

FERROMAGNETS AND ELECTROMAGNETS

• Only certain materials, such as iron, cobalt, nickel, and gadolinium, exhibit strong magnetic effects, called ferromagnetic (latin word for iron: ferrum)

Neodymium 

- the most widely used type of rare-earth magnet; a permanent magnet made from an alloy of neodymium, iron, and boron.

ELECTROMAGNETISM

• use of electric current to make magnets

Hans Christian Oersted- A compass needle was deflected by a current-carrying wire

Large Hadron Collider-  a giant magnetic particle accelerator

Properties of Magnetic Field Lines

1. The direction of the b-field is tangent to the field line 

2. The strength of the field = closeness of the lines; It is proportional to the number of lines per unit area perpendicular to the lines (areal density)

3. Never cross. The field is unique 

4. Are continuous; forming closed loops without beginning or end. From north to south pole

 THE HALL EFFECT

• discovered by Edwin Hall

• The Hall Effect is used to determine whether positive or negative charges carry current.

• The process involves creating a voltage difference across an electrical conductor, influenced by an electric current and an applied magnetic field perpendicular to the current.

Magnetic Force on a MOVING CHARGE

• A moving charge moving into B-Field will experience MAGNETIC FORCE; this deflection (a change in a moving object's velocity) is 3d

Conditions for the forces are:

1. Must have a magnetic field present

2. Charge must be moving

3. Charge must be + or -

4. Charge must be moving PERPENDICULAR to the field

RIGHT HAND RULE

Determining the direction of the force on a POSITIVE charge

• The Fingers = Direction of B-Field

• The Thumb = Direction of velocity

• The Palm = Direction of the Force

** Use LEFT HAND for NEGATIVE charges

Lorentz Force- the combination of the magnetic and electric force on a point charge due to electromagnetic fields.

MAGNETIC FORCE and CIRCULAR MOTION

• Magnetic force = Centripetal force; used to solve for the circular path

Charges moving in a wire

• If the wire had a current (moving charges), it’ll experience force when placed in a B-Field

• The B-Field is being produced by EXTERNAL LIGHT

Using Right Hand Rule

• The thumb will represent the direction of the CURRENT instead of the velocity

Why does the wire move?

• The wire itself is magnetic– has its own internal magnetic field that is attracted or repulsed by the EXTERNAL FIELD;

• The wires OWN internal magnetic field makes concentric circles round the wire 

The MAGNITUDE of the INTERNAL FIELD

• B-Field (B) is directly proportional to the Current (I), and inversely proportional to the circumference