Magnetism and Electromagnetic Induction PHYSICS 1-2 MR. CHUMBLEY CHAPTER 19: MAGNETISM CHAPTER 20: ELECTROMAGNETIC INDUCTION

Magnets and Magnetic Fields CHAPTER 19, SECTION 1 P

Early Magnets  The term magnet comes from the Latin magnetum, which means “lodestone”  Lodestone (leading stone) was used to help indicate direction because it could be used to build early compasses

Early Magnets

Magnetic Domains  The cause for magnetism is the motion of electric charge  In naturally occurring magnetic materials this is due to the fact that the electron moves in two ways:  Revolution around the nucleus  Rotation about its own axis  When there is a net spin of multiple electrons in a direction, then the atoms of that material gain magnetic properties, and are called ferromagnetic

Magnetic Domains  As large groups of ferromagnetic atoms group together they can form areas where their magnetic properties align  A magnetic domain is a region composed of a group of atoms whose magnetic fields are aligned in the same direction

Magnetic Domains

Magnetic Fields  Like in electricity, there also exists a magnetic field  A magnetic field is a region in which a magnetic force can be detected  As with electric fields, magnetic fields can be indicated using magnetic field lines

Magnetic Fields

Magnetism and Electricity CHAPTER 20, SECTION 2 P

Magnetic Field and Current  In 1820, Hans Christian Ørsted demonstrated that when a compass was brought near a current carrying wire, there was a deflection in the needle of the compass  The magnetic field here is circular and in a plane perpendicular to the wire

Right-Hand Rule #1  The direction of the magnetic field produced by an electric current is also described as a right-hand rule  Thumb points to the direction of current  Fingers wrap around the wire indicating the direction of the magnetic field

Sample  Determine the direction of the magnetic field if wire is carrying a current from:  Left to right  Right to left  Top to bottom  Back to front

Solenoids  A solenoid is a long, helically wound coil of insulated wire  Since there are many loops of wire, the strength of the magnetic field intensifies

Homework!  P. 668 #1-3  P. 672 #1-2

Magnetic Force CHAPTER 19, SECTION 3 P

Charged Particles in a Magnetic Field

Right-Hand Rule #2  The direction of the force is determined by a right hand rule  Fingers point in direction of the magnetic field  Thumb points to the direction of motion  Palm points to the direction of magnetic force acting on a positive charge

Sample Problem 19A (p. 675) A proton moving eastward experiences a force of 8.8 × N upward due to the Earth’s magnetic field. At this location, the field has a magnitude of 55 μT to the north. Find the speed of this particle. Given: q = 1.60 × C B = 5.5 × T F = 8.8 × N Unknown: v = ?

Current-Carrying Conductor in a Magnetic Field

Right-hand Rule #3  There is another right-hand rule that describes the force acting on a current carrying wire the moves through a magnetic field  Fingers point in the direction of the magnetic field  Thumb points in the direction of conventional current  Palm points to the direction of magnetic force

Sample Problem 19b (p. 678) A wire 36 m long carries a current of 22 A from east to west. If the magnetic force due to Earth’s magnetic field is downward (toward Earth) and has a magnitude of 4.0 × N, find the magnitude and direction of the magnetic field at this location. Given: l = 36 m I = 22 A F = 4.0 × N Unknown: B = ?

Magnetic Force of Parallel Wires

Homework!  Practice A (p. 675)  #1-3  Practice B (p. 678)  # 2, 4

Electricity from Magnetism CHAPTER 20, SECTION 1 P

Electromagnetic Induction  In 1831 Michael Faraday discovered that an electric current could be created by moving a conductor through a changing magnetic field  Electromagnetic induction is the process of creating a current in a circuit loop by changing the magnetic flux in the loop  Magnetic flux ( Φ M )is the number of field lines that cross a certain area perpendicularly

Ways to Induce a Current  A circuit can be moved in and out of a magnetic field  A circuit can be rotated in a magnetic field  The intensity and/or direction of a field is varied  All of these create a change in magnetic flux acting through the conductor

Lenz’s Law  When a magnetic field induces a current in a conductor, that current also produces a magnetic field  The nature of the induced magnetic field was described by Heinrich Lenz  Lenz’s Law states:  The magnetic field of the induced current is in a direction to produce a field that opposes the change causing it

Faraday’s Law of Electromagnetic Induction

Generators, Motors, and Mutual Inductance CHAPTER 20, SECTION 2 P

Generators and Alternating Current  An electric generator is a machine that converts mechanical energy into electrical energy using electromagnetic induction  Generators can produce both alternating and direct current, but generally are used to produce AC  Alternating current is an electric current that changes direction at regular intervals

Motors  And electric motor is a machine that converts electrical energy into mechanical energy

AC Circuits and Transformers CHAPTER 20, SECTION 3 P. 707 – 714

Alternating Current  Since alternating current is a constantly fluctuating value, determining the amount of current, voltage, and resistance in a circuit can be difficult  For AC circuits, the effective current is used rather than the constantly changing values  The rms current (root-mean-square) is the value of alternating current that gives the same heating effect that the corresponding value of direct current does

AC versus DC

RMS Current

Transformers

 The primary coil is where the current comes from initially  The secondary coil is where the voltage is changed and then transmitted  Increasing the voltage is called stepping-up  Decreasing the voltage is called stepping-down

Sample 20C (p. 712)  A step-up transformer is used on a 120 V line to provide a potential difference of 2400 V. If the primary has 75 turns, how many turns does the secondary have?

Electricity Transmission

Homework!  Practice C (p. 713) #1-5