Magnetism Chapter 36-37 LHS Physics Duke

Read Chapter 36 Page 562 – 574 Take at least two sentences for each section There are nine sections

Hewitt – Magnetism Video https://www.youtube.com/watch?v=0pGeOER_zB0

Hewitt – Electromagnetic Induction https://www. youtube. com/watch

Permanent Magnets Naturally occurring magnets (called lodestones) have been known for over 2000 years The Chinese were using magnets as compasses when the first Europeans visited. Magnets today are used in: motors, TVs, tape recorders, microphones

Magnets and Magnetic Fields Magnets have two poles North and South Like poles repel and unlike poles attract Magnetic fields by convention start at the north pole and go to south pole If you break a magnet each piece still has two poles; you never get an isolated magnetic pole.

Permanent Magnets Magnets are created due to small magnetic domains inside a material on the microscopic level. As the domains align, the material will exhibit the magnetic properties. Iron magnets are considered magnetically soft since they gain and lose magnetic fields easily. magnetic domain

More on Magnets Nickel and Cobalt magnets and ceramic magnets are considered hard magnets. Once the domains of hard magnets are aligned, the domains are not easily disordered.

General Properties of Magnets Magnets can temporarily polarize some conductors, making them magnets as well. Magnetic poles always come in pairs. No magnetic monopoles have been found. Can be made of exotic material combinations such as ALNICO (Aluminum, Nickel, and Cobalt) or rare-earth elements such as neodymium.

Magnetic Fields

Interaction between Magnetic Fields

Magnetic field is represented by the letter B and is measured in Tesla’s (T) In the plane of the page  Into the page x x x x x Out of the page (towards reader) ● ● ● ● ●   

Lets think about the Earth The GEOGRAPHIC North pole is the earth’s MAGNETIC south pole The GEOGRAPHIC South pole is the earth’s magnetic north pole WHY??? S N Because the north end of a compass has to point which direction? SOUTH!!

Variable Magnetic Fields Variable magnetic fields are produced by moving charges per time (Current = I) You will need to learn the three right hand rules For a current carrying wire, For a current carrying wire around a conductor, For current moving in a magnetic field.

Magnetic Fields Terms F = Force (measured in Newton’s) B = Magnetic field strength (measured in Tesla) I = Current (measured in amperes) L = Length of wire (measured in meters) q = Charge (measured in Coulombs) v = Velocity (measured in m/s)

Right Hand Rule for current in a wire – Use your right hand Point your thumb in the direction of positive current flow Fingers point the direction that is a magnetic South Pole – the direction of the field lines +

Electromagnet The magnetic field, B, around a wire with current, I, running through the wire creates a magnetic field that is circular in shape. In fact, the magnetic field is concentric circles never overlapping.

Right Hand Rule for a wire around a conductor Grab the coil with your thumb point in the direction of the current flow. Your fingers represent the Magnetic Field, B, and will point towards the South Pole.

How to create an electromagnet? A straight wire creates a coiled magnetic field. A coiled wire creates a straight magnetic field inside the coils. If you know the direction of the current you can determine the direction of the field.

Right Hand Rule for charges moving in a magnetic field The palm represents the direction of the Magnetic Force, FB. The thumb pointed in the direction for positive current; which is v, I, or q. The fingers point in the direction of the magnetic field, B. All the vectors are perpendicular for maximum force.

Right Hand Rule for charges moving in a magnetic field Correlation image is pg 774 B = FB/(qv) (THEORY) B = Magnetic field measured in Teslas (T) FB = Magnetic Force q = charge v = velocity FB = qvB equation on page 773

Force Caused by Magnetic Fields Ampere noted that an electric current creates a magnetic field like a permanent magnet. Since a magnet field exerts a force on a permanent magnet a current carrying wire should experience a force when placed in a magnetic field

Force due to a wire B = FB/(Il) FB = Force (measured in Newtons, N) B = Magnetic field strength (measured in Tesla, T) I = current (measured in Amperes, A) l = length of wire (measured in Meters, m) L instead of a script l FB = B I l or FB = B I L

Tesla The unit, Tesla, measures how strong the magnetic field is at a point. Earth’s Magnetic Field ~ 5 x 10-5 T = 50mT Small bar magnet ~ 0.01 T Strong Lab Magnet ~ 10 T