Download Electricity and Magnetism Pt 2

Electricity and
Magnetism
Ch 17-18 Objective:
Describe how electricity and magnets do
work.
1/9 Bell Work
• What is one thing you can do differently to be
better in school? Explain.
1/9 Schedule
• Review Circuits
• Notes Ch 18.1 “Magnets and Magnetic Fields”
• Investigating Magnets Activities
If you drop this class, turn in your book!
Assignments:
Review Circuits and
Diagrams
• Series
Ibattery = I1 = I2 = I3 = ...
ΔVbattery = ΔV1 + ΔV2 + ΔV3 + ...
Rtotal = R1 + R2 + R3 + ...
• Parallel
Vbattery = V1 = V2 = V3 = ...
Itotal = I1 + I2 + I3 + ...
1/Rtotal = (1/R1) + (1/R2) + (1/R3) + ...
Review Circuits and
Diagrams
Draw a quick circuit diagram and solve the following
problems.
• Calculate the total resistance for 650, 350, and 1000
ohm resistors connected in series.
• A 10, 20, and 100 ohm resistor are connected in
parallel. Calculate the total resistance.
Ch 18.1 “Magnets and
Magnetic Fields”
Objectives:
〉Explain what causes a magnet to attract or
repel another.
〉Describe Earth’s magnetic field orientation.
Magnets in Everyday Life
1. Name five uses for magnets.
2. Why is a compass a useful tool for navigation?
Magnets in Everyday Life
3. Earth has magnetic N pole and the
geographic North Pole. Are they located at
the same geographic location?
4. Where do you think the magnetic S pole is
located?
Magnets
Magnetic pole: one of two points that have
opposing magnetic qualities
o All magnets have at least one pair of poles, a north pole and a south
pole.
Magnets
Some materials can be made into magnets.
• Iron is a soft magnetic material.
• Easily magnetized.
• Tends to lose its magnetic properties easily.
•
• Cobalt is a hard magnetic material.
• More difficult to magnetize.
• Once magnetized, it doesn’t lose magnetism easily.
Temporary paperclip magnet
Magnetic Fields
Magnets repel or attract because of the
interaction of their magnetic fields.
• magnetic field: a region where a magnetic force
can be detected
• Magnets
• Moving charges (aka electric current) create
magnetic fields.
Magnetic Fields
• Field lines are used to represent a magnetic field.
o Field lines always form closed loops from N to S.
o The magnetic field gets weaker with distance.
o Lines close together indicate a strong field.
o Field lines farther apart indicate a weaker field.
Magnetic Fields
• Compasses align with Earth’s magnetic field.
o The compass points in the direction that lies along the
magnetic field line at a given point.
o By convention, the pole of a magnet that points north
is often painted red.
Earth’s Magnetic Field
ALERT!!
Earth’s magnetic field lines run from
geographic south to north.
• Antarctica is a magnetic north pole.
• Northern Canada is magnetic south pole.
Earth’s Magnetic Field
Earth’s magnetic field has both direction and
strength.
• The source is not yet fully understood.
o The iron in the core is too hot to retain any magnetic properties.
o The circulation of charged particles in the liquid layer of the core may
be the source.
• The sun also has a magnetic field and ejects
charged particles into space.
Investigating Magnets
Activities
Bar Magnet
o Hang a taped magnet parallel to the counter.
o Determine how to figure out which end is N and S.
o Could you determine N and S if both magnets were
covered?
Compass
• Hold compass parallel to ground.
• Determine if the colored part of the needle is attracted
to N or S of a bar magnet.
• What kinds of objects shift the needle towards them?
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Tatianna
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1/10 Bell Work
Knowledge is knowing a tomato is a fruit. Wisdom is
not putting it in a fruit salad.
- Peter Kay, English comedian
• What is the difference between knowledge and
wisdom?
1/10 Schedule
• Notes Ch 18.2 “Magnetism from Electric Current”
• Start Electromagnet and Compass Lab
o Wear goggles
o Disconnect the wire when not in use, gets HOT!
If you drop this class, turn in your book!
Assignments:
Ch 18.2 “Magnetism from
Electric Current”
Objectives:
〉Explain what happens to a compass near
electric current.
〉Describe how electric motors function.
Electromagnetism
Electric currents produce magnetic fields.
〉Strong, steady current moves the compass
needles to align with the magnetic field.
〉A “Right Hand Rule” determines magnetic
field direction.
〉 By convention, current is the flow of positive charges.
〉 Flows from + end of battery, through wire toward negative end.
Current Right-Hand Rule
1. The thumb points in the
direction of the current.
2. Fingers point in the direction
of the magnetic field.
Ex: The magnetic field runs
counterclockwise.
Current Right-Hand Rule
Practice:
1. Point thumb towards I+.
2. Curl fingers for magnetic field.
I
Show field direction.
• Arrows = direction on page
• Dot = point out of page
• X = point into page
Electromagnetism
• Moving charges cause magnetism.
• All matter is made of atoms.
o Negative electrons moving around the nuclei of atoms.
o Electrons spin.
o Protons (+) move.
•
Circuits connected to batteries, outlets, etc. create
magnetic fields.
Polarity Right-Hand Rule
Used to find N/S in an electromagnet.
1. Curl fingers on right hand in direction of current.
2. Thumb points at North pole.
N
Electromagnetism
• Solenoids and bar magnets have similar magnetic
fields.
• solenoid: a coil of wire with an electric current in it
o The field of each loop of wire adds to the strength of the magnetic field.
o More loops OR more current creates a stronger magnetic field.
• electromagnet: a coil that has an iron core and that
acts as a magnet when an electric current is in the
coil
o The magnetic field of the rod adds to the coil’s field.
Electromagnetic Devices
Electric motor = Electromagnet
• electric motor: a device that converts electrical
energy to mechanical energy
• Galvanometers can detect, measure, and
determines direction of current.
Electric Motor
Ch 18.3 Electric Currents
from Magnetism
Objectives:
〉Explain what happens when a magnet is
moved into or out of a coil of wire.
〉Relate electricity and magnetism.
Linking Batteries and
Outlets
1. List as many items as you can that use DC
current/batteries.
2. List as many items as you can that use AC
current/outlets.
3. What is the function of the AC wall adapters like
cell phone chargers?
4. Electric power that goes into a neighborhood
must decrease in voltage before it goes into a
home. Explain why this is necessary.
Electromagnetic
Induction
Electromagnetic induction: the process of
creating a current in a circuit by changing
a magnetic field
〉Moving a magnet causes charges in the
wire to move.
〉aka Faraday’s law
Electromagnetic
Induction
• Other induction options:
o Rotate the circuit
o Changing the strength of the magnetic field
• Electromagnetic induction obeys Law of
Conservation of Energy.
o Pushing a loop through a magnetic field requires work.
Electromagnetic
Induction
Electromagnetic
Induction, continued
• Magnetic force acts on moving electric charges.
o The force maximum value when the charge moves perpendicularly
to the field.
o As the angle between the charge’s direction the magnetic field
decreases, the force on the charge decreases.
• The magnetic force acts on wires carrying a
current.
Electromagnetic
Induction
Charges move = current
Charges stationary = no current
Electromagnetic
Induction
Generators convert mechanical energy into
electrical.
• generator: a machine that converts mechanical
energy to electrical energy
• alternating current (AC): an electric current that
changes direction at regular intervals
o For each half rotation of the loop, the current produced by the
generator reverses direction.
• AC generators produce the electrical energy
you use in your home.
AC Generator
Induced Current
The Electromagnetic Force
Electricity + Magnetism = Electromagnetism
〉2 parts of the same force
〉 The energy that from these two forces is called
electromagnetic (EM) energy.
o EX: Light, radio, microwaves, ultraviolet
o Made up of oscillating electric and magnetic fields that are
perpendicular to each other.
Slinky Lab
Define – amplitude, transverse wave, longitudinal
wave, crest, trough
• Stretch slinky, but don’t break it.
• What is a pulse?
• What is the equation for speed?