Light & Sound BRHS- Physics 2012

Electromagnetic Radiation Energy that has properties of both particles and waves Particles – have mass and occupy space Waves – no mass but carry energy

Electromagnetic Radiation – ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/nature.h tm

Wave properties Amplitude – the height of the waves

Wave properties Frequency ( ) – the number of waves that pass a given point per unit of time units of hertz (Hz or s –1 ) Low High

Wave properties Wavelength ( ) – the distance between a crest and a crest or a trough and a trough in m or nm

Relationship of frequency and wavelength Frequency x wavelength = speed = c (speed of light) c = x 10 8 m/s

1. Lasers used with DVD players have a wavelength of 650 nm. What is the frequency of this light in hertz (Hz)?

2. Calculate the frequency of yellow light that has a wavelength of 584 nm. 3. Calculate the wavelength in nm of violet light having a frequency of 7.32 x Hz.

Electromagnetic Radiation Figure 7.10 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

Electromagnetic Radiation Fig 3.3

Continuous Spectra White light passed through a prism produces a spectrum – colors in continuous form. ~ 650 nm ~ 575 nm ~ 500 nm ~ 480 nm ~ 450 nm The different colors of light correspond to different wavelengths and frequencies Fig 7.11 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

Line Spectra Fig 7.12 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

Line Spectra The pattern of lines emitted by excited atoms of an element is unique = atomic emission spectrum Fig 7.13 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

Fig 7.17 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry ΔE level = h

Demonstration with light items

1905 Albert Einstein – photons  energy packets explained the photoelectric effect E = h h = x 10 –34 joules (J) Planck’s constant

Fig 7.15 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

Sound moves in waves through a medium (air) having a random arrangement of molecules in a constant rate that is recognized by the ear

If sound hits a soft surface, the wave moves around the object, but if it hits a rigid surface, 1. a wave is set up within the material and is a function of the composition of the material 2. rest of the energy is reflected in waves like light off a mirror as a function of distance

If sound hits a surface with a small hole, the wave moves through the hole in waves, If 2 or more holes are present, diffraction occurs

diffraction  when waves add (reinforce or constructive interference) or subtract (nulls or destructive interference)

constructive interference – sound gets louder destructive interference – sound gets softer Sound effects easily observed by the ear

Intensity = Energy Time x Area Intensity = Power Area OR

Sound Ranges Humans can hear sounds between 20Hz Hz Ultrasonic waves are waves above 20000Hz; Infrasonic waves are waves below 20Hz Most bat and dog communication is ultrasonic while elephants and whales are infrasonic s&safety_mode=true&persist_safety_mode=1 &safe=active

Pitch How the brain interprets the frequency of an emitted sound. higher the frequency, the higher the pitch. lower the frequency, the lower the pitch Frequency is in 1 Hertz = 1 vibration/sec

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Demonstration with tuning forks Smaller forks have higher pitch Larger forks have lower pitch

Demonstration with Physics of Music Experiencing pitch

Doppler Effect Christian Doppler ( ): An Austrian physicist who conducted experiments with musicians on railway trains playing instruments as the train approached them and receded from them.

Doppler Effect The Doppler Effect is a change in pitch, due to the relative motion between a source of sound and the receiver. common example: change in pitch as a car horn or siren on a vehicle moves past us

Doppler Effect Illustrated

Doppler Effect Applications Radar Gun Measure the speed at which a pitcher throws Catch speeder Track the motion of precipitation caused by storm clouds Ultrasound Measure the rate of blood flow in the arteries or the heart. Light “Red-shift”-calculate galaxy speeds As other galaxies move away from us, the light has a lower frequency than if it were at rest.