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Waves and Radiation

Waves and Radiation. Wave Parameters and Behaviours. Learning Outcomes. Energy can be transferred as waves. Determination of frequency, wavelength, amplitude and wave speed for transverse and longitudinal waves.

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Waves and Radiation

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  1. Waves and Radiation Wave Parameters and Behaviours

  2. Learning Outcomes • Energy can be transferred as waves. • Determination of frequency, wavelength, amplitude and wave speed for transverse and longitudinal waves. • Use of the relationship between wave speed, frequency, wavelength, distance and time. • Diffraction and practical limitations. • Comparison of long wave and short wave diffraction.

  3. Energy can be transferred as waves Imagine trying to lift someone up a distance of 5m. It is actually hard work. You need lots of energy to do it. Now think about how the waves lift up ships in the ocean. Where is the energy coming from to lift these massive ships? See Virtual Nation 5 Physics – Waves Introduction

  4. Energy in Waves • All waves transfer energy from one location to the other. • Waves may be transverse – water waves, radio waves, etc or longitudinal like sound waves. See Virtual Nation 5 Physics – Transverse and Longitudinal Waves

  5. Speed of Sound in Air

  6. The speed of sound in air is less than the speed of light in air. This can be seen, for example, during a thunderstorm. You can see the lightning before you hear the thunder (unless the storm is overhead).

  7. Speed of sound = 340 m/s Speed of light = 300 000 000 m/s = 3 x 108 m/s Speed of light is MUCH FASTER.

  8. Methods for Measuring the Speed of Sound in Air

  9. When measuring the speed of sound we need a DISTANCE and a TIME.

  10. Method 1 • A pupil with a source of sound (e.g. cymbals) stands at one end of a field. • At the other end is a pupil with a stop-watch. • The length of the field is measured in metres. • The timekeeper starts the watch when they see the cymbals coming together. • When the timekeeper hears the sound, the watch is stopped and the time noted in seconds.

  11. Pupil with cymbals Pupil with stop-watch There will always be an uncertainty with this – so repeat experiment and take an average (mean) time. Then use d = vt to calculate speed of sound. Distance

  12. Method 2 A more accurate method uses a computer and timer interface to measure the time interval. Timer / Computer Hammer Microphone X Microphone Y Metal Plate Distance

  13. The distance between the microphones is measured with a metre stick. • Hitting a metal plate with the hammer makes a loud sound. • When the sound reaches microphone X, the timer starts timing. • When the sound reaches microphone Y, the timer stops timing.

  14. Typical Results • Distance between microphones = 1.0 m • Time on timer = 3 ms = 0.003 s (ms is a millisecond which is 1/1000 s) • Speed of sound = distance / time = 1 / 0.003 = 330 m/s

  15. 2005 Q15

  16. Video – Calculating Speed • http://www.bbc.co.uk/scotland/learning/learningzone/clips/23

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