 Waves and Energy Transfer Chapter 15 pages 250-265.

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Waves and Energy Transfer Chapter 15 pages 250-265

Brief Review or Quick Introduction n Transverse wave- wave moves perpendicular to the medium. –Examples: surface water waves, light waves n Longitudinal waves- wave moves parallel to the medium. –Examples: deep water waves, sound waves, seismic waves

The Shape of a Wave wavelength crest trough wavelength amplitude wavelength Rest position

Frequency and Period n The frequency is the number of vibrations per second. –Abbreviated “ f ” –Measured in Hertz (Hz) = 1/s n The period is the amount of time between each crest. –Abbreviated “ T ” –Measured in seconds f = 1 T T= 1 f

Velocity Velocity = distance time n In this case the distance between each crest is equal to the wavelength. n The distance between each crest is the period. Velocity = wavelength period V = T

Velocity ctd. Velocity = wavelength period But frequency = 1 period = wavelength x 1 period So… Velocity = wavelength x frequency

Example n A sound wave with frequency 262 Hz has a wavelength of 1.29 m. What is the velocity of the sound wave? = 338 m/s Velocity = wavelength x frequency Velocity = 1.29 m x 262 Hz

Example n A radio wave has a frequency of 99.5 MHz (99.5 x 10 6 Hz). What is its wavelength? (speed = 3 x 10 8 m/s) 3.02 m Velocity = wavelength x frequency frequency Velocity = wavelength frequency 3 x 10 8 m/s = 99.5 x 10 6 Hz

Example n A typical light wave has a wavelength of 580 nm. (speed = 3 x 10 8 m/s) What is its frequency? 5.2 x 10 14 Hz Velocity = wavelength x frequency wavelength Velocity = frequency wavelength 3 x 10 8 m/s = 580 x 10 -9 m

Summary n Speed = wavelength x frequency n Frequency = 1 / Period n Speed = wavelength / Period n Wavelength = Speed / frequency n Frequency = Speed / wavelength n Period = wavelength / speed

Interference n Result of the superposition of two or more waves. n Principal of Superposition says that two or more waves that are in the same medium add together algebraically.

Interference n Result of the superposition of two or more waves. n Principal of Superposition says that two or more waves that are in the same medium add together algebraically. CONSTRUCTIVE INTERFERENCE

Interference n Result of the superposition of two or more waves. n Principal of Superposition says that two or more waves that are in the same medium add together algebraically.

Interference n Result of the superposition of two or more waves. n Principal of Superposition says that two or more waves that are in the same medium add together algebraically. DESTRUCTIVE INTERFERENCE

Waves meeting walls n Reflection –Waves bounce of a wall at the same angle n Refraction –Waves bend when they pass through a barrier n Diffraction –Waves spread out when they go through an opening.

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