HNRT 227 Fall 2015 Chapter 6 Wave Motion, Sound and Electromagnetism 17 September 2015 presented by Prof. Geller.

HNRT 227 Fall 2015Chapter 6

Wave Motion, Sound andElectromagnetism17 September 2015presented by Prof. Geller

Recall from Chapters 1-5 Units of length, mass and time, and metric Prefixes Density and its units The Scientific Method Speed, velocity, acceleration Forces Falling objects, Newton’s Laws of Motion and Gravity Work, Potential Energy and Kinetic Energy Conservation of Energy, Types/Sources of Energy Kinetic Molecular Theory, Temperature and Heat Phases of matter and Thermodynamics Electricity Magnetism

Forces and Vibrations Vibration

back and forth motion Amplitude

extent of displacement from the equilibrium position Cycle

one complete vibration Period

time required to complete one cycle Frequency

number of cycles per second Relationship between period and frequency

T = 1 / f f = 1 / T

WavesLongitudinal

disturbance that causes particles to move closer together or farther apart IN THE SAME DIRECTION the wave is moving

Transverse disturbance that causes motion PERPENDICULAR

to the direction that the wave is movingIn general, liquids carry longitudinal waves

but not transverse waves Transverse waves, such as water waves, dissipate

all their energy at the phase interfaceWe use same terms as vibrations, for wavesv =* f

Sound WavesSound does not travel in a vacuumSound moves through solids faster

than any gasVelocity of sound is effected by

composition and temperature of gas

Reflection, Refraction and InterferenceReflection

waves bouncing back off of a boundaryRefraction

change in direction of wave crossing a boundary

Interference interaction of waves

destructive interferenceconstructive interference

ResonanceNatural frequency

frequency of vibration determined by the object’s composition and shape

Resonance when frequency of external force

matches natural frequency

Doppler Effect and Sonic Boom

Doppler Effect Apparent change in frequency of a

wave caused by the relative motion of the source or observerpitch of train approaching, departing

Sonic boom shock wave caused by object

moving at speed of sound or faster

ElectromagnetismMagnetic Fields

generated by electric currentEnergy conversion

electric motors electric generators speakers

Maxwell’s Equations summary of electromagnetic laws and

interactions…

WavesTypes of waves

longitudinale.g. sound

transversee.g. electromagnetic waves

Velocity, frequency and wavelength wave velocity = wavelength times

frequencywatch your units

ElectromagnetismElectricity according

to Gauss relates electricity to

electric chargeFaraday’s Law

relates electric fields to magnetic fields

Magnetism according to Gauss relates magnetism to

electricity

Maxwell’s EquationsAmpere-Maxwell Law

relates magnetic field to electricity

Maxwell unifies electricity and

magnetism into electromagnetism

Electromagnetic InteractionsTransmission vs. opacityAbsorption vs. emissionScattering

refraction reflection diffraction interference

Electromagnetic Spectrum Visible

Red (~7000 A or 700 nm) Orange, Yellow, Green,

Blue, Indigo Violet (~4000 A or 400 nm)

More than meets the eye radio, microwave, infrared,

ROYGBIV (visible), ultraviolet, X-rays, gamma rays

from lowest energy to highest energy

from longest to shortest wavelength

from lowest to highest frequency

Reflection and Refraction (not all in text)Reflection

the angle of incidence is equal to the angle of reflection

i = r

Virtual image light rays appear to originate from

Real image light rays really do meet here

Refraction change of direction of light n = c / v [defines index of refraction]

Diffraction, Interference and Polarization (not all in text)Diffraction

light rays appear to bend around the edge of an object

Interference light rays interacting with other light

rays causing reinforcement or canceling or some combination of the two

Polarization vibrates/oscillates in a single plane

Doppler ShiftA change in measured frequency caused by

the motion of the observer or the source classical example of pitch of train coming towards

you and moving away wrt light it is either red-shifted (away) or blue-

shifted (towards)