Introduction

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

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

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

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

5. END of Light and Sound

6. Interference double slit screen Light & Sound Introduction 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. • Bright (constructive interference) and dark (destructive interference) fringes are formed on the screen.

7. Back to Light & Sound Introduction 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.

8. Waves Sources Detectors Uses 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 Light & Sound EM Waves Next Slide • The complete electromagnetic wave spectrum is shown below (in descending order of wavelength) :

9. Waves Sources Detectors Uses Ultraviolet Waves Sun, objects with very high temperature Film, Fluorescent materials Sterilisation, checking of banknote, producing fluorescent light X-rays X-ray tube Film, Medical use Gamma rays Radioactive nuclei Film, GM counter Medical use, thickness gauge, dating process Light & Sound EM Waves Next Slide

10. Frequency Wavelength EM Waves 3  105 -1010Hz 103 -10-2 m Radio & TV wave Microwave 3  1010Hz 10-2 m 3  1012Hz 10-4 m Infra-red 4  1014 -8 1014Hz 4  10-7 -7 10-8m Visible light Ultraviolet 3  1016Hz 10-8 m X-rays 3  1018Hz 10-10 m Gamma rays 3  1021Hz 10-13 m Back to Light & Sound EM Waves Click Back to • The wavelengths and frequencies of different kinds of EM waves are shown below :

11. Light & Sound Sound 1 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.

12. direction of travel at rest position t = 0 t =1/8 T t =1/4 T t =3/8 T t =1/2 T t =5/8 T t =3/4 T t =7/8 T t =1 T Back to Light & Sound Sound 1 Click Back to • A longitudinal wave is shown below :

13. person signal generator Back to Light & Sound Sound 1 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. • Interference of sound happens and hence the man passes through maxima and minima of the sound wave successively.

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

15. Light & Sound Sound 1 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.

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

17. CRO speaker microphone signal generator balloon with carbon dioxide Back to Light & Sound Sound 1 Click 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.

18. rarefaction compression C R C R C R C R C R C R C R C   Back to Light & Sound Sound 2 Click 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.

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

20. Back to Light & Sound Sound 2 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.

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

22. Light & Sound Sound 2 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)

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

24. Light & Sound Sound 2 Next Slide • If a sound wave produces a sine curve on a CRO, than the sound is a pure note. • The sound waves produced by different kinds of musical instrument have complex regular patterns which are not sine curves. • 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.

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

26. Light & Sound Sound 2 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.

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