Magnetism Chapter 36

What is a Magnet? Material or object that produces a magnetic field. Two types:  Permanent  Electromagnet

What causes Magnetism? In order to create a magnetic field, a charged particle must be moving. Moving and spinning electrons cause magnetic fields in every object.

Domains A small region of space where the magnetic fields produced by moving electrons are aligned together. Often, the directions of the domains cancel each other out. Ferromagnetic material  Cancellations do not occur, resulting in a net magnetic field

Domains

Magnetism Opposites poles attract Like poles Repel Magnetic Poles can not be separated  Every object that has a north pole has a south pole

Magnetism

Magnetic Field Region around a moving charged particle through which a force is exerted on another moving charged particle Similar to Electric Fields

Magnetic Field Lines Lines are not real North  South (outside magnet) Can not cross Closer lines mean stronger field

Magnetic Field Lines

Magnetic Field Magnetic Field is a region around a moving charged object through which a force is exerted on another moving charged particle Motion of particle must be perpendicular to the magnetic field

Magnetic Fields Magnetic Fields are often illustrated using arrows

Magnetic Fields What about into the page or out of the page? Out of Page Into Page

Magnetic Hand Rules To determine the direction of the force, we use hand rules. Different hands for different charges  Right hand for Positive charges  Left hand for Negative charges

Conventional Current Conventional Current follows the old “convention” that positive charges are the charges that are moving in current Use Right Hand Rule

Electron Current Electron Current is the reality that negative charges are the charges that are moving in current Use Left Hand Rule

Magnetic Hand Rules Point index finger in direction of motion Point palm or other fingers in direction of magnetic field Point thumb in direction of Magnetic Force

Example An electron is moving through a magnetic field as shown below. In what direction will the magnetic force be? Out of page e

Another Example An electron is moving through a magnetic field as shown below. In what direction will the magnetic force be? Down e

Force on Wire Still use hand rule to determine the direction of the magnetic force Index finger is the direction of the current

Magnetic Fields produced by Currents A current carrying wire also produces a magnetic field Direction follows second Hand Rule

Magnetic Fields produced by Currents Second Hand Rule Thumb in direction of current Curl fingers around wire Curled fingers show direction of magnetic field

Example What is the direction of the magnetic force exerted on wire 2 by the magnetic field produced by wire 1? I-I- I-I- 1 2 Down

Example What is the direction of the magnetic force exerted on wire 1 by the magnetic field produced by wire 2? I-I- I-I- 1 2 Down

Magnetic Fields produced by current carrying loops Imagine current flowing through the loop below In what direction will the magnetic field be produced inside the loop? Into Page I-I-

Electromagnets Temporary magnet caused by an induced magnetic field from current carrying wires.

Electromagnets Current carrying wire produces a magnetic field Coiling the wire bunches up the magnetic field inside the coil

Electromagnets Increasing the strength of the electromagnet:  Increase Current in wire  Increase number of coils  Add an iron core

Electromagnetic Induction If charged particle moving through a magnetic field feels a force, shouldn’t a moving magnetic field exert a force on a charged particle?

Electromagnetic Induction A voltage can be “induced” in a wire by moving a magnet near the wire.  often a coil of wire is used Faraday’s Law  Induced voltage is directly proportional to the number of coils, cross-sectional area of the coils, and rate of change of magnetic field

Electromagnetic Induction

Inducing a current in a coil of wire creates its own magnetic field

Electromagnetic Induction Changing direction of magnetic field changes direction of induced voltage  Creating an alternating current (AC)

Alternating Current  Current alternates direction at a regular rate Electrical Outlets Direct Current  Current flows in one direction only Batteries Sim

Generators & Motors Device to convert between Electrical and Mechanical Energy Generator  Converts Mechanical Energy to Electrical Energy Motor  Converts Electrical energy to Mechanical Energy

Generator

Motor

Electromagnetic Induction Current flowing through a coil wires produces a magnetic field A changing magnetic field induces a current in an adjacent coil

Electromagnetic Induction Using AC produces a consistent changing magnetic field Adding an iron core strengthens the magnetic field

Transformer Device used to increase or decrease voltage using electromagnetic induction

Transformer Complete loop is more efficient

Transformers V = voltage N = number of coils

Transformers Step Up Transformer  Secondary has more coils than primary  Resulting Voltage is larger Step Down Transformer  Secondary has less coils than primary  Resulting voltage is lower

Conservation of Energy Energy transferred must be equal  Power is equal

Electric Field An electric field is produced by a charged particle A changing electric field can be produced by a moving charged particle A changing electric field produces a magnetic field

Electromagnetic Induction A changing magnetic field also induces an electric field When magnetic fields and electric fields are produced they are at right angles to each other

Electromagnetic Wave Oscillating electric and magnetic fields that regenerate each other (light) No medium is required

Electromagnetic Radiation Only one speed can preserve this regeneration Speed of Light is 300,000,000 m/s  3 x 10 8 m/s Discovered by James Clerk Maxwell

Maxwell’s Equations