Unformatted text preview:

11.2 Waves• Wave properties– speed– wavelength• Example wave on a string• Superposition of waves• Reflection of waves at an interfaceWaves• A wave is a disturbance that propagates through distance with a certain speed. (traveling waves)• The disturbance carries energy but does not carry mass. • Mechanical Waves- water wave, sound –propagate through matter.• Electromagnetic Waves – radio, x-ray, light – can propagate through a vacuum.Wave on a stringincreasing timeTransverse Wave - The displacement is perpendicular to the direction of propagation – No displacement in direction of propagation.Longitudinal Wave- The displacement is parallel to the direction of propagation –Pressure wave.Transverse and Longitudinal WavesTransverse and Longitudinal Waves• The transverse and longitudinal waves depend on different mechanical properties of the material.• Two polarizations of transverse waves. Longitudinal waves are unpolarized.• The speed of the transverse and longitudinal waves are different.• Longitudinal waves but not transverse waves can propagate in a fluid.Examples• Transverse waves– Transverse wave on a string– Electromagnetic waves (speed = 3.00x108m/s)• Longitudinal waves– Sound waves in air (speed = 340 m/s)2Seismic waves are transverse and longitudinalP waves- longitudinalfasterv~ 5000 m/s (granite)S waves – transverseslowerv~ 3000 m/s (granite)Seismograph record after an earthquake.Time →Which one is transverse and which is longitudinal?Simple Harmonic WavesPeriodic displacement vs distanceHarmonic oscillationsWavelength - Spatial PeriodWave travels distance λ during one period TWave velocityvfTλ==λThe wave travel at a velocity of one wavelength in one period.ExampleA radio station transmits at a frequency of 100 MHz. Find the wavelength of the electromagnetic waves. (speed of light =3.0x108m/s)vf=λvfλ=863.0x103.0m100x10==3Transverse wave on a stringv ->uv is the wave speedu is the speed of the string perpendicular to direction of v.The mass at P undergoes simple harmonic motion.Transverse wave simulationtransverse wavehttp://www.surendranath.org/applets/waves/Twave01A/Twave01AApplet.htmlSpeed of the transverse wave on a string.FFV ->x∆m∆mx∆µ=∆mass densityFv =µspeed of transverse wave on a string depends on the tension onthe string and the mass densityExampleA transverse wave with a speed of 50 m/s is to be produced on a stretched spring. If the string has a length of 5.0 m and a mass of 0.060 kg, what tension on the string is required.Fvm/L=2vmFL=2(50m / s) (0.060kg)30N5.0m==Superposition Principle• When two waves overlap in space the displacement of the wave is the sum of the individual displacements. Interference• Superposition of harmonic waves depends on the relative phase of the two waves• Can lead to– Constructive Interference– Destructive Interference4Constructive Interferencedistance →Wave 1Wave 2SuperpositionThe two waves have the same phaseDestructive InterferenceWave 1Wave 2SuperpositionThe two waves are out of phase (by 180o, or π)Distance ->Other Interference EffectsMany other effects arise from superposition of harmonic waves – discussed later.Standing waves. two waves traveling in opposite directions.Beats. two waves with different frequencies.Diffraction. Interference in wave patterns in space.Reflection and Transmission.• When a wave reaches a boundary, part of the wave is reflected and part of the wave is transmitted. • The amount reflected and transmitted depends on how well the media is matched at the boundary.• The sign of the reflected wave depends on the “resistance” at the boundary.Mis-match at the boundaryBoundarymatchmis-matchmis-matchpart of the wave will be reflected at the boundaryReflectionFixed End-InversionFree End-No Inversionstrong


View Full Document

UCSD PHYS 1C - Waves

Download Waves
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Waves and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Waves 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?