light & sound brhs- physics 2012. electromagnetic radiation energy that has properties of both...

Light & SoundBRHS- 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 – www.google.images

http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/nature.htm

Wave propertiesAmplitude – the height of the waves

Wave propertiesFrequency () – 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 = 2.998 x 108 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 1014 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 SpectraFig 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



ΔElevel= h

Demonstration with light itemshttp://www.hsphys.com/light_and_optics.ht

ml

1905 Albert Einstein – photons energy packets explained the photoelectric effect

E = hh = 6.626 x 10–34 joules (J)

Planck’s constant

http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html

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

http://www.mrfizzix.com/instruments/basics.html

http://www.mrfizzix.com/instruments/basics.html

Intensity = Energy

Time x Area

Intensity = Power

Area

OR

Sound Ranges

www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc

Humans can hear sounds between 20Hz- 20000Hz

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

http://www.youtube.com/watch?v=iWfjcdOcwRs&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

tonie3c.blogspot.com

www.healthinformation.nhs.uk

scienceblogs.com

Demonstration with tuning forks

Smaller forks have higher pitch

Larger forks have lower pitch

Demonstration with Physics of Music

Experiencing pitch

Doppler EffectChristian Doppler (1805-1853): 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

http://boomeria.org/physicslectures/secondsemester/light/astronomy/doppler.jpg

http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/pics/bt2lf0615_a.jpg

Doppler Effect ApplicationsRadar Gun

Measure the speed at which a pitcher throwsCatch speederTrack the motion of precipitation caused by storm cloudsUltrasoundMeasure 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.

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