PHY 102 S08

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• Activity B1-WA due by 4 pm Friday 03/28
• Chapter 5 Mallard HW quiz Due by 12 AM
  Thursday 03/27
• Chapter 5 quiz in class on Thursday 03/27

Tuesday, March 25 Spring 2008
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Electricity and Magnetism

• Chapter 5

Great Idea Electricity and magnetism are two
different aspects of one forcethe
electromagnetic force
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Batteries and Electrical Current

• Electrical current
• Flow of charged particles
• Symbol I
• Units Coulombs/second (C/s)
• Voltage
• the difference in electrical charge between two
  points in a circuit (electrical pressure)
• Symbol V
• Units volts (V)
• Battery
• Converts chemical energy to kinetic energy
  (energy of flowing charges)

4
Electric Circuits

• Electric circuit
• Unbroken path of material carrying electricity
• Circuit components
• 1. Source
• 2. Closed path
• 3. Device to use electrical energy
• Ohms Law
• Current is directly proportional to voltage V and
  inversely proportional to resistance R
• In symbols I V / R
• Electric Power P I V

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Magnetic Effects from Electricity

• Oersted
• Magnetic field created by motion of electrical
  charges
• Magnetic Monopole
• Does not exist
• Magnetism is related to arrangement of electrical
  charges in atoms
• Electromagnet

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Electric Motors Magnetism
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Electrical Effects from Magnetism

• Faraday
• Electromagnetic induction
• Electrical fields and currents can be produced by
  changing magnetic fields
• Electric Generator

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Maxwells Equations

• Coulombs Law
• No magnetic monopoles
• Magnetic phenomena produced by electrical effects
• Electrical phenomena produced by magnetic effects

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Waves Electromagnetic Radiation

• Chapter 6

Great Idea Whenever an electrically charged
object is accelerated, it produces
electromagnetic radiationwaves of energy that
travel at the speed of light
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Waves
A wave is a traveling disturbance that transports
energy from one place to another without
transporting matter across the intervening
distance.
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Simple Oscillations

• Oscillation back-and-forth motion about an
  equilibrium position
• Cycle one complete oscillation or repetition of
  a periodic motion
• Period, T the length of time required for one
  cycle
• Frequency, f number of cycles that occur during
  a unit of time f 1 / T
• Amplitude distance traveled above or below
  equilibrium position

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Properties of Periodic Waves
A periodic wave is a wave made of a series of
pulses separated by equal time intervals.
l
f
v
time between wave crests
Speed of wave v f l
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Sample Exercise
Suppose that water waves have a wavelength of 1.4
m and a period of 0.8 s. What is the frequency
of these waves? What is the velocity of these
waves?
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Sample Exercise
A wave on a rope is shown in the diagram. a.
What is the wavelength of this wave? b. If the
speed of the wave is 6 m/s, what is its frequency?
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Two Basic Wave Types

• Longitudinal wave motion in same direction as
  wave
• Transverse wave motion perpendicular to wave
  direction

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Sound Waves
A sound wave is a periodic longitudinal wave of
pressure variations propagating through a medium.
http//electronics.howstuffworks.com/speaker5.htm
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Sound Waves
The shapes of instruments and the materials
theyre made of influence the pitch and timbre of
the sound they create...

• Pitch of sound is determined by its frequency and
  speed
• High frequency high pitch low frequency low
  pitch

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Sound Waves

• Sound waves travel at about 340 m/s ( 760 mi/h)
  in air

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Doppler Effect
Apparent shift in frequency of a wave emitted
from or received by a moving source
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Wave Interference

• Constructive Interference
• Add together
• Destructive Interference
• Cancellation

wave addition
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Electromagnetic Waves
Self-propagating radiant energy Energy
transferred by oscillating electric and magnetic
fields created by accelerated charges
Electromagnetic waves continue through internal
mechanisms and transfer energy as they travel
they do not require a medium to travel.
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Speed of Light
All electromagnetic waves travel at the same
speed
v f l c
c 3 108 m/s 186,000 mi/s
Energy of wave E hf (h is Plancks constant
6.626 10-34 m2kg/s)

• Higher frequency visible light blue color
• Lower frequency visible light red color

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Interaction of EM Waves Matter

• Transmission
• wave passes through matter
• refraction dispersion
• Absorption
• wave energy are absorbed
• Scattering
• wave energy absorbed and reemitted
• diffuse scattering
• reflection

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The Blue Sky Light Scattering
Molecules in the air preferentially scatter high
frequency blue light waves sky appears blue
when viewed away from direct sunlight
http//math.ucr.edu/home/baez/physics/General/Blue
Sky/blue_sky.html
Sky appears white around the Sun
yellow/orange/red when light traverses long
distances through the atmosphere
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Electromagnetic Waves the Doppler Effect
Apparent shift in frequency of a wave emitted
from or received by a moving source

• Higher frequency light blueshifted
• Lower frequency light redshifted