Transcript T 03/25 Week 11, Chapter 5/6

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
Electricity and Magnetism
Chapter 5
Great Idea:
Electricity and magnetism are two different
aspects of one force—the electromagnetic force
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)
Electric Circuits
• Electric circuit
– Unbroken path of material carrying electricity
• Circuit components
1. Source
2. Closed path
3. Device to use electrical energy
• Ohm’s Law
– Current is directly proportional to voltage V and
inversely proportional to resistance R
– In symbols: I = V / R
• Electric Power: P = I × V
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
Electric Motors & Magnetism
Electrical Effects
from Magnetism
• Faraday
– Electromagnetic induction
– Electrical fields and currents
can be produced by
changing magnetic fields
• Electric Generator
Maxwell’s Equations
• Coulomb’s Law
• No magnetic monopoles
• Magnetic phenomena produced by
electrical effects
• Electrical phenomena produced by
magnetic effects
Chapter 6
Waves & Electromagnetic
Radiation
Great Idea:
Whenever an electrically charged object is
accelerated, it produces electromagnetic
radiation—waves of energy that travel at the
speed of light
Waves
A wave is a traveling disturbance that transports energy from
one place to another without transporting matter across the
intervening distance.
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
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
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?
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?
Two Basic Wave Types
Longitudinal wave –
motion in same direction
as wave
Transverse wave –
motion perpendicular to
wave direction
Sound Waves
A sound wave is a periodic longitudinal wave of pressure
variations propagating through a medium.
http://electronics.howstuffworks.com/speaker5.htm
Sound Waves
The shapes of instruments and the materials they’re 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
Sound Waves
L=½l
Sound waves travel at about 340 m/s (≈ 760 mi/h) in air
Doppler Effect
Apparent shift in frequency of a wave emitted from
or received by a moving source
Wave Interference
– Constructive Interference
• Add together
– Destructive Interference
• Cancellation
wave addition
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.
Speed of Light
All electromagnetic waves
travel at the same speed
v=f l=c
c = 3 × 108 m/s = 186,000
Energy of wave:
E = hf
mi/s
(h is Planck’s constant
= 6.626 × 10-34 m2·kg/s)
Higher frequency visible light = blue color
Lower frequency visible light = red color
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
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/
BlueSky/blue_sky.html
Sky appears white around the Sun
– yellow/orange/red when light traverses
long distances through the atmosphere
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”