Section 3 Sound and Light How do dolphins

Section 3: Sound and Light How do dolphins detect objects in murky water?

Sound waves are produced by compression and rarefaction of vibrating objects: Compression: forward movement. Creates regions of high density Rarefaction: backward movement. Creates region of low density.

Sound and Us: We hear frequencies from 20 to 20, 000 Hz • Below 20 Hz is infrasonic • Above 20, 000 Hz is ultrasonic

Speed of sound in various objects: Higher density objects tend to have a higher speed of sound.

Parts of a sound Wave: 1) Wave front: area of compression 2) Wave length: distance from one compression to the next 3) Ray: Arrow indicating the direction of wave

Doppler Effect: Q: Does the speed of a sound wave depend on the pitch or frequency? Q: What will happens to the distance between the waves in front of the source as it moves forward? How about behind? Results: Check the following web site http: //landau 1. phys. virginia. edu/classes/109 N/more_stuff/flashlets/doppler. htm

Doppler effect continue… • Waves in front of source become closer because waves cannot get away. • Waves in back of source get longer. • Shock waves are produced when source is traveling faster than speed of sound

Resonance: Natural frequency: Frequency an object vibrates at. Swing/desk/ jar/ guitar/ • • Demo: Music Demo: Spring Demo: Tacoma bridge Demo: Electric guitar and wine glass How to break a tree Designing cars Designing engines

Standing wave in pipes open at both ends: Node: Regions of high and low compression that form within a pipe. Anti-node: Regions where the pressure remain unchanged. Fundamental frequency: natural frequency of pipe. Longer pipes have lower frequencies.

Fn = n v / (4 L) Fn: fundamental frequency or frequency of pipe (hz) n: number of nodes L: length of pipe v: speed of sound wave (343 m/s for air)

Problem: Find the frequency given off by a 2. 03 meter pipe, for nodes 1 through 3. Frequency Nodes Frequency

Light: Has alternating electric and magnetic fields and travels at 3 x 108 m/s.

Electromagnetic Spectrum: Range of all of the frequencies of light.

Visible Spectrum: Range of visible frequencies of light

More properties of waves: Refraction: The bending of light as it passes from one medium to the other

Diffraction: The bending of a wave around an object.

Polarization: When all of the directions of the light waves are aligned.