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 components1. Source2. Closed path3. 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

Waves & Electromagnetic Radiation

Chapter 6

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.

• 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

Simple Oscillations

Properties of Periodic Waves

Speed of wave: v = f

f

v

time between wave crests

A periodic wave is a wave made of a series of pulses separated by equal time intervals.

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?

Longitudinal wave –

motion in same direction

as wave

Transverse wave –

motion perpendicular to

wave direction

Two Basic Wave Types

A sound wave is a periodic longitudinal wave of pressure variations propagating through a medium.

Sound Waves

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 = ½

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

– Constructive Interference• Add together

– Destructive Interference• Cancellation

Wave Interference

wave addition

Electromagnetic Waves

Self-propagating radiant energyEnergy 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

Higher frequency visible light = blue color

Lower frequency visible light = red color

c = 3 × 108 m/s = 186,000 mi/s

v = f = c

All electromagnetic waves travel at the same speed

Energy of wave: E = hf (h is Planck’s constant

= 6.626 × 10-34 m2·kg/s)

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

Sky appears white around the Sun – yellow/orange/red when light traverses long distances through the atmosphere

http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html

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”