1. Force, Energy & Communication Lesson 13 & 14 WAVES

2. Lesson objectives Re-establish that all sound is caused by vibrations (waves) Revise the links between pitch and wavelength; volume and amplitude. Know a method for calculating the speed of sound Learn the basic wave equation Measure the critical angle for a glass block

3. WAVES – the basics Turn to p 158 of PHYSICS text book

4. WAVES – the basics Waves vibrate in a regular fashion.

5. WAVES – the basics All sound waves are caused by vibrations.

6. WAVES – the basics Waves can transfer energy or information from one place to another.

7. WAVES – the basics While the wave may transfer information or energy, it does not transfer matter.

8. WAVES – the basics Nearly all the information we transfer is done by waves e.g. sound, radio, mobile phones, tv, etc

12. Measuring the speed of sound using the echo method

14. Speed = distance / time

15. Measuring the speed of sound using the echo method Expt. no.Distance from wall (m) No. of claps Total distance travelled Time (s)Speed of sound (m/s) 14910 24910 34910 44910

16. Measuring the speed of sound using the echo method Expt. no.Distance from wall (m) No. of claps Total distance travelled (m) Time (s)Speed of sound (m/s) 149109803.62 249109803.31 349109804.01 449109803.54

17. Measuring the speed of sound using the echo method Text book value for the speed of sound through air is…..

18. Measuring the speed of sound using the echo method Text book value for the speed of sound through air is…..330 m / s

19. The Wave Equation A formula you are expected to KNOW!!

20. The Wave Equation Turn to page 171 in the text book.

21. The Wave Equation The wavelength ( )of a wave depends on two things: 1the frequency of the wave 2the speed of the wave

22. The Wave Equation This can be expressed by the wave equation

23. The Wave Equation This can be expressed by the wave equation speed (m/s) = frequency (Hz) X wavelength (m)

24. The Wave Equation This can be expressed by the wave equation speed (m/s) = frequency (Hz) X wavelength (m) N.B. frequency is measured in Hertz (or kilohertz). Hertz is another way of saying the number of waves in a second. E.g. 30 Hz = 30 waves every second

25. The Wave Equation Copy out the example calculation off p171

26. Total Internal Reflection Refraction happens when light is coming out of something dense like glass or water. If the angle of the light is shallow enough, the light ray won’t come out at all but reflects back into the dense substance. This is called total internal reflection because all the light reflects back in. The angle over which total internal reflection occurs is called the critical angle.

27. The Wave Equation

28. Measuring the critical angle Follow the instructions on your experiment sheet.

29. HOMEWORK Complete all questions on the sheet on “Sound waves”. Due in next Thursday