Physics 2 Unit 5 Waves, Light, & Sound

Polarization

blocks TRANVERSE waves of a certain axis of oscillation. Two polarizers in 90 degree = no light. Any angle between will have less intensity/energy going through

Phase difference

Constructive = 0 or 360 degrees, whole # of wavelengths.

Destructive = 180 or any multiple. .5, 1.5, 2.5 wavelengths

Standing waves

When waves with the same amplitude and frequency but opposite propagation. interfere with each other creating the appearance of a wave that isn’t moving set antinodes and nodes.

v=f*lambda, and its amplicatiosn

v depends on the medium, not the wave

f is a property of the wave.

Lambda depends on speed (and thus medium too)

Two types of waves

electromagnetic+tranverse, longitudinal+mechanical (needs medium, like sound).

Waves transfer…

Energy and momentum but not mass.

Pulse vs wave

Pulse is a single oscillation. Wave has to be PERIODIC, repeated pulses.

Longitundal waves

require medium, compressions and rarefractions, movement is parallel to propagation.

v = sqrt(F_T/(m/L))

velocity depends on the force on the medium/string (tension) and the mass density (mass divided by length). Tighter, thinner string has most speed.

Temperature

Sound travels fast when warmer bc it is mechanical and particles are moving faster with more energy/collisions

what is always true of two waves in the same medium?

They are traveling at the same speed.

Graphing a longitudinal wave

time vs pressure, amplitude is loudness. Use sin, -sin, cos, -cos.

Graphing E&M graph

time or position vs electric field or magnetic field strength. Formula is Atrig(2πx/T) substitute x and T as necessary

Types of reflection

Soft reflection, to lower index, no phase change

Hard reflection: from lower to higher index, phase change

Intensity of light can be measured by

Power/Area. Amplitude is proportional to Intensity but no the same. Intensity decreases as you move away from source because more area.

What can you find from an A vs x graph?

wavelength, amplitude. NOT period/frequency bc not in terms of time.

What happens as a wave reaches a boundary?

Reflection, transmission, and absorption. Refraction

How does a particle behave with higher wavelengths

Higher wavelength means lower f (if light), meaning less particle-like and more wave-like, lower energy and momentum. Less diffraction

Experimental design for wave tension/velocity

pulse generator, taut rope, atwood and block to vary F_T. or if its wave, measure the # of sec/# of cycles and do multiple trials.

Harmonic/Sound Exp. Design

Ruben’s tube (gas holes). Tone generator, meter stick, frequency detector (to verify), thermometer. Graph λ = v*T

Dopppler Effect

Closer waves bunch up, so frequency goes up when wavelength goes down, blue shift. Red shift is farther away. Based on relative motion. Nonconstant change in frequency if there’s acceleration. Rapid change in “percieved velocity” as object passes you. Rest frequency

Beats

superposition/interference of waves that are slightly out of phase. The more offset the waves, the quicker and louder the beat/standing wave. Note: only made from wave not pulses

Harmonics

Sound, longitudinal vibrations of air molecules

Differ based on if the ends are fixed or closed.

Both ends fixed/open: λ = 2/(harmonic #*L), or f = (harmonic #)f

One end open: λ = 4/(odd # * L)

Single Slit Diffraction

Fraunhofer diffraction: far enoguh away si that lines from the source can be considered parallel (theta is same)
Wave spreads out because of interference of individual particles. Pattern of constructive/destructive based on phase differences of particles.

y_min (distance from center to first node) = m*λ*D/a

where m is order (which node), D is distance from source to screen, a is width of slit

the shorter part of the slit is the one that spreads out.

Single center dot is width of TWO maxima

What can be said in diffraction if the angle is small?

sintheta = tantheta = theta. So therefore,

x= mλL/d

What affects diffraction

More diffraction with larger λ, smaller opening

Double Slit Diffraction

Typically one brigh spot with gradient on the sides. Rainbowing caused by different in wavelengths.

Further sits = less distance between maxima. Closer λ to object (within a factor of ten, more diffraction)

y_max = mλD/d, where d is distance between slits, D is screen to slits, y is distance between antinodes. Single center dot is width of ONE maxima, not two.

What is ∆D

∆D is the path difference between the particles from each slit. If it is an integer multiple of λ, or where m is an integer 0,±1,±2, then constructive. If .5s then destructive.

Values of m

remember that m measures ANTINODES in double slit, but NODES in single slit. To find the other, you need to take .5’s of m

Experimental Design for Diffraction

Diffraction grating, shine lasers, calculate distance, use distance to find angle, then you know the m to find λ

Resonance

When an external force or vibration matches an objects’ resonant frequency, defined as the frequency that generates the maximum amplitude response in the system

Thin Flim Interference

Things like water drops have reflection at both their inner and outer surfaces that interfere, causing some λs that are brighter/dimmer. Be careful with phase changes at each interface. Film is a THIN layer that is close in thickness to λ. The interference depends on n, λ, and thickness.

Film inteference with 0 or 2 phase changes

λ_film = 4T/(even #) if constructive, odd # if destructive

T is thickness

Film Interference for 1 phase change

λ_film = 4T/(odd #) if constructive, even # if destructive

T is thickness