2. Light & Sound Wave nature of light Transverse wave with a speed of 300,000,000 m/s Next Slide Reflection, refraction and diffraction of light Interference of light : Young’s double slit experiment Diagram Introduction

3. Light & Sound Electromagnetic waves Light is a kind of electromagnetic waves Next Slide Electromagnetic spectrum Diagram EM Wave

4. Light & Sound Introduction Sound is a longitudinal wave which transmits energy Next Slide Properties of sound Diagram Interference of sound Diagram Diffraction of sound Diagram Clap-echo method Diagram Refraction of sound Diagram Sound 1

5. Light & Sound Travelling of sound wave Next Slide Compression and rarefaction Diagram Note and Noise Pitch (frequency), loudness (amplitude) and different patterns of sound wave shown on a CRO Diagram Fundamental frequency, overtones and quality of sound Diagram Sound 2

6. END of Light and Sound

7. Light & Sound Next Slide A compact monochromatic source of light (filament of a lamp) is placed behind a double slit as shown below. The two slits become 2 compact sources of light which emit light waves with same wavelength, frequency and speed. screendouble slit Interference Bright (constructive interference) and dark (destructive interference) fringes are formed on the screen. Introduction

8. Light & Sound Click Back to The wavelength of light is very small. The separation and the width of the slits must be small enough to be comparable with the wavelength of light, otherwise fringes (interference pattern) will not appear on the screen. Back to Introduction

9. Light & Sound Next Slide The complete electromagnetic wave spectrum is shown below (in descending order of wavelength) : WavesSourcesDetectorsUses Radio & TV Waves Radio & TV transmitter Radio set & TV set Broadcasting of TV and radio programs Microwaves Microwave transmitter & oven Microwave receiver Broadcasting of TV programs, oven, radar, satellite communication Infra-red Sun, objects with medium or high temperatures Thermometer, skin, Phototransistor, film Medical IR photography, solar oven, IR navigation system Visible light Sun, objects with high temperatures Eyes, film, Photocell EM Waves

10. Light & Sound Next Slide WavesSourcesDetectorsUses Ultraviolet Waves Sun, objects with very high temperature Film, Fluorescent materials Sterilisation, checking of banknote, producing fluorescent light X-raysX-ray tubeFilm,Medical use Gamma raysRadioactive nuclei Film, GM counter Medical use, thickness gauge, dating process EM Waves

11. Light & Sound Click Back to The wavelengths and frequencies of different kinds of EM waves are shown below : Back to Gamma rays X-rays Ultraviolet Visible light Infra-red 3  10 10 Hz Microwave 10 3  10 -2 m3  10 5  10 10 Hz Radio & TV wave Wavelength Frequency EM Waves 3  10 12 Hz 4  10 14  8  10 14 Hz 3  10 16 Hz 3  10 18 Hz 3  10 21 Hz 10 -2 m 10 -4 m 4  10 -7  7  10 -8 m 10 -8 m 10 -10 m 10 -13 m EM Waves

12. Light & Sound Next Slide Sound wave is a longitudinal wave which travels in gas, liquid or solid. Sound wave is the vibration of particles in matter. Therefore, it cannot travel in vacuum. In a longitudinal wave, the vibration of particles is always parallel to the direction of travel of the wave. Sound 1

13. Light & Sound Click Back to A longitudinal wave is shown below : Back to Sound 1

14. Light & Sound Click Back to Two loudspeakers are connected to the same signal generator. If a person walks as shown, he will hear a sound of varying intensity. Back to Interference of sound happens and hence the man passes through maxima and minima of the sound wave successively. signal generator person Sound 1

15. Light & Sound Click Back to Someone can hear another even when he is behind a doorway. It is due to the diffraction of sound wave. Back to Wavelength of sound wave is comparable to the size of the barrier. person wall sound wave Sound 1

16. Light & Sound Next Slide Since sound wave is reflected by a straight barrier, we can use the so-called clap-echo method to find the speed of sound. A person stands facing a wall which is at least 100 m away. He claps his hand at a constant rate. Echoes would be heard. He should adjust his clapping rate so that the echoes are always heard exactly mid-way between the claps. Since the clapping rate and the distance between the person and the wall is known, we can calculate the speed of sound. Sound 1

17. Light & Sound Click Back to Back to person wall echo d frequency : f Sound 1

18. Light & Sound Click Back to Back to Since the speed of sound in carbon dioxide is much smaller than that in air, we can observe the refraction of sound as sound travels from air to carbon dioxide. A balloon with carbon dioxide can be thought as a convex lens which converges the sound wave to microphone. signal generator CRO speaker microphone balloon with carbon dioxide Sound 1

19. Light & Sound Click Back to Back to At certain parts of sound wave, the particles are close to each other. These parts are called compression. At other parts, the particles are far away from each other. These parts are called rarefaction. Distance between successive compressions or rarefactions is equal to a wavelength. compression rarefaction CCCCCCCCRRRRRRR Sound 2

20. Light & Sound Next Slide A CRO is shown below : A sound can be shown as a transverse wave pattern on a CRO. Sound 2

21. Light & Sound Click Back to Note : sound wave with regular vibrations. For example, a tuning fork (shown on the right ) or a musical instrument can produce a note. Noise : sound wave with irregular vibrations. Back to Sound 2

22. Light & Sound Next Slide Sound with a high pitch has a larger frequency than sound with a low pitch. The audible frequency range for human beings is 20 Hz to 20000 Hz. Sound with large loudness has a larger amplitude than sound with small loudness. Sound 2

23. Light & Sound Next Slide Different patterns on CRO for various kinds of sound waves are shown below : sound with high pitch (large f and small T) sound with low pitch (small f and large T) Sound 2

24. Light & Sound Click Back to sound with large loudness (large A) sound with small loudness (small A) Back to Sound 2

25. Light & Sound Next Slide If a sound wave produces a sine curve on a CRO, than the sound is a pure note. Different musical instruments produce sound waves of different regular patterns even though they play the same note. We say that each of these sounds has its own quality. The sound waves produced by different kinds of musical instrument have complex regular patterns which are not sine curves. Sound 2

26. Light & Sound Next Slide Various patterns of sound waves on a CRO are shown : tuning folk violin piano All sound waves shown have the same period (frequency) but different quality. Sound 2

27. Light & Sound Next Slide The complex pattern is formed from the sum of a primary sine wave and a number of smaller sine waves. The smaller sine waves have frequencies which are multiples of that of the primary sine wave. The primary sine wave with a chosen frequency is called the fundamental, while the smaller sine waves with multiples of the chosen frequency are called overtones. The proportion of overtones in a sound wave depends on the kind of musical instrument. Therefore, different musical instruments produce sound waves of different qualities. Sound 2

28. Light & Sound Click Back to The combination of fundamental and overtones is shown below : Fundamental Overtone (2 times the frequency of the fundamental) Resultant Back to Sound 2