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Waves

Waves. Sending energy at different wavelengths. Outline. Waves and Solar Energy Definitions and Descriptions Sources and disturbances Velocity and the medium Frequency and Wavelength. Solar Energy. What is Solar Energy? Nuclear fusion in the Sun’s core.

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Waves

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  1. Waves Sending energy at different wavelengths

  2. Outline • Waves and Solar Energy • Definitions and Descriptions • Sources and disturbances • Velocity and the medium • Frequency and Wavelength

  3. Solar Energy • What is Solar Energy? • Nuclear fusion in the Sun’s core. • Heating up the core to 40,000 K, and the surface to 6,000 K. • How does Solar Energy get here? • Conduction? – heat transfer through contact • Convection? – through transport of matter • Radiation! – through the emission of electromagnetic waves • EM waves can transport energy through a vacuum and over billions of miles!

  4. Waves • -- A disturbance in a medium which carries energy but not matter. • Disturbance – can be a single pulse or a repeated (periodic) vibration. • Medium – Something through which waves can travel (water, air, strings, etc.) • Transverse waves – the disturbance of the medium is perpendicular to the motion of the wave. • Longitudinal waves – motion of the medium is in the direction of the motion of the wave.

  5. Characteristics of Waves velocity A λ • A = amplitude is the displacement of the medium from equilibrium. • λ = wavelength is the distance along the direction of motion between repeating points on the wave. • T = period is the time it takes for the wave to repeat itself. • v = velocity is the rate at which the wave is moving through the medium.

  6. Wave velocity and the medium • The velocity of a regular or periodic wave is just • v = λ / T • Example: λ = 2 m and T = 4 seconds. • v = 2m / 4s = .5 m/s. • The velocity of waves is primarily a function of the medium. • vsound in air = 340 m/s • vsound in water = 1500 m/s • vsurface water waves = 2 m/s • vlight = 3 x 108 m/s

  7. Wave Speed: a comparison • Certain events produce both light and sound simultaneously. • We detect them at different times because of the different wave speeds in the media. • You’re a distance of 1 mile (1.6km) away. • v = d / t --- so, t = d / v. • tsound = 1600 m ÷ 340 m/s = 5 sec • tlight = 1600 m ÷ 3 x 108 m/s = 5 x 10-6 s

  8. Wave frequency • Frequency, f, is the inverse of the period, T. • f = 1 / T. • Period is the time it takes for a wave to repeat itself – frequency is the number of times a wave repeats itself in one second • Measured in Hertz: 1 Hz = 1 cycle per sec. • Now, v = λ / T = λ f

  9. v = λf; λ = v/f; f = v/λ • Example 1: • AM radio 1000 has f =1000 kHz or 1 MHz. • Since v = 3 x 108 m/s, • λ = 3 x 108 m/s ÷ 1 x 106 Hz = 300 m! • Example 2: • The highest frequency we can hear is 20,000 Hz. • λ = 340 m/s ÷ 20,000 Hz = .017 m = 1.7 cm

  10. The Audible Spectrum C above C above

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