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SOUND, , 8, , Eperiment, , Introduction..., , Wavesat, Waves are vibratory disturbance in a medium which carries energy from one point, to another without there, , being a direct contact between the two points., , The wave which travels along a spring (or slinky) when it is pushed or pulled at an, end, are longitudinal waves., , Sound is a sequence of wave which propagates in a medium., When a wave of sound energy travelling in a medium strikes another medium, , called the refilecting surface), it bounces offin another direction in the first medium, in which it was travelling. This is called the reflection of sound wave., Sound waves are longitudinal waves i.e., in which particles of the medium vibrate, back and forth in the same direction in which wave is moving., , To verify the laws of reflection of sound., , THEORY:, The laws of reflection of sound state:, 1. The angle of incidence is always equal to the angle of reflection., 2. The incident sound wave, the normal at the point of incidence, and the reflected sound wave lie in the, same plane., , MATERIALS REQUIRED:, Acellotape, a large drawing sheet, geometry box, wooden board, two toothpicks, two metal tubes each of length, about 30 cm and 2 cm in diameter, which are polished from inside and are very smooth, a stopwatch., , METHOD:, 1. Fix a drawing sheet on the laboratory table using a cellotape., , 2. Draw a line PQ, towards the upper edge ofthe drawing sheet. Marka point O on it, in the middle. Draw, a perpendicular NO to meet the line PQ at O., 3. Keep the wooden board (reflecting surface) on the line PQ. It should be in vertical position, with the, , help of plasticine, or keeping a, , block of wood behind it., , 4. Fix a toothpick A using cellotape to the inner side of one metal tube. Similarly, fix toothpick B on the, inner side of the other metal tube., 5., , Place the metal tube with toothpick A on the drawing sheet, on the left side of the normal, such that, , it makes an angle of about 30" to 40 with the normal No. Make sure that the end of the toothpick A, meets the, , 6., , point O., , Similarly, place the other metal tube with toothpick B on the drawing sheet, on the right side ofthe normal, , AR AMenIel IY, , E
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toothpicks, , flat metal plate held, in vertical position, , plasticine, , -, , plasticine, , K-----, , Q, , toothpick held, , hollow metal tube, , with cellotape, , C, , N, normal, , stopwatch, , ear, , Figure 8.1, , such that the end of the toothpick B meets the point O. Make sure that the end of the second tho ., , the metal, , tube projects out from the table edge, so that you can place your ear comfortably at the end of the ha, , e tube., , 7. Place, , a, , cardboard sheet, , vertically along NO, , to, , prevent sound from, , source, , to, , 8. Place a ticking stopwatch close to the end of the metal tube on left hand side., 9. Place your, , directly reach your eaear, , of the metal tube on right hand side. Gently move the tube sidewavs, till the sound of the stopwatch is heard clearly., Using a sharp pencil, mark the lines of the toothpicks A and B. Extend the lines, as shown in, figure 8.1, Measure the angle of incidence (left side of nomal, NO) and angle of reflection (right side of the nomal NO, With angle of incidence 35°, 40°, 45°,, repeat the same procedure. Measure the angle of reflection in, , 10., , 11., , ear, , close to the end, , each case., , OBSERVATION, S. No, , Angle of incidence, , Angle of reflection, , 1., , 2, 3., 4, , CONCLUSION, 1., , The, , angle, , of incidence is, , equal to the angle of reflection within, experimental limits., 2. Since the incident sound, wave, the reflected sound, wave and the normal lie on the same, sheet, hence they lie in the same, plane., 3. Thus, the laws of reflection of, sound are, verified., , draw
