Physics Chapter 1 Form 5

1. Chapter 1: Waves Form 5 1 Physics Next > The study of matter

2. Objectives: ( what you will learn ) 1) understanding Waves 2) reflection of waves 3) refraction of waves 4) diffraction of waves 5) interference of waves 6) analysing sound waves 7) analysing electromagnetic waves Physics: Chapter 1 2 < Back Next >

3. Understanding Waves: Physics 3 1. A wave is a traveling disturbance from a vibrating or oscillating source. 2. A wave carries energy along with it in the direction of its propagation. 3. A wave is a mean of energy transfer through vibration. < Back Next >

4. Transverse Wave Waves 4 Particles in the medium vibrate in a direction perpendicular to the direction of wave propagation. Perpendicular = 90 o to the line of direction. Examples : wave in a rope water waves light waves < Back Next >

5. Longitudinal Wave 5 Particles in the medium vibrate in a direction parallel (0 o to line of direction) to the direction of wave propagation. Examples : wave in a slinky spring sound wave Waves < Back Next >

6. Surface Waves 6 Waves This is both transverse waves & longitudinal waves mixed in one medium. Examples : earthquake or seismic wave shear wave in a slinky spring < Back Next > Wavefront A surface on the wave where all particles vibrate in phase (coming together to the same level). Oscillations Vibration or oscillation of particles in a medium is like oscillation of simple pendulum or loaded spring.

7. 7 Waves Complete Oscillation Complete cycle; e.g. motion from A to B & back to A. Amplitude, a Maximum displacement from equilibrium position that is halfway between crest (high) & trough (low). Period, T Time taken for a complete oscillation. Frequency, f Number of complete oscillation in one second; f = 1/T < Back Next >

8. 8 Waves < Back Next > Speed of wave, v Distance traveled by wave per second, v = f λ Free Oscillation Occurs when a system oscillates without any external force acting on it. Natural Frequency, f n Frequency of a free oscillation. Simple pendulum l = length, g = gravity Loaded vertical spring m = mass, k = constant

9. 9 Waves Damped Oscillation An oscillation whose amplitude decreases due to energy loss from the system (as heat to air resistance). Forced Oscillation An oscillation produced when a system is forced into oscillation by an external periodic force. Resonance Occurs when a system which is forced into oscillation oscillates with large amplitude ; the condition being that the frequencies of both systems are equal to each other. < Back Next >

10. 10 Reflection of Waves Angle of reflection = angle of incidence Reflected wave has same speed, frequency, & wavelength as the incident wave. Angle of reflection , r = Angle of incidence , i < Back Next > λ λ i r v v

11. 11 Refraction of Waves Refraction of wave The change in velocity of wave when it travels from one medium to another. Water & light waves are refracted towards Normal when moving into shallower or denser region (frequency unchanged, speed & wavelength decrease), and away from Normal the other way round. But sound waves behave in the opposite way. (Try relate it to the resistances of medium) < Back Next >

12. 12 Diffraction of Waves Diffraction is the spreading of waves after passing a narrow slit or an obstacle. Waves are diffracted more if: a. the slit is narrower b. the wavelength is longer Light has very short wavelengths, diffraction occurs only for slits with width of 10 -4 m or less. Sound has long wavelengths, diffraction of sound waves enable sound to go around corners . < Back Next >

13. 13 Interference of Waves Principle of superposition of waves Displacement y, produced by 2 waves at a point is the vector sum of displacements y 1 & y 2 produced by each of the waves. y = y 1 + y 2 Interference = effect produced by superposition of waves from 2 coherent sources. Coherent sources = if they oscillate in phase, or antiphase, or with same phase difference & they have the same frequency. < Back Next >

14. 14 Interference of Waves antinode : constructive superposition from 2 crests or troughs node : destructive superposition from crest & trough Separation between 2 consecutive antinodal or nodal lines at distance D from the 2 sources: Young’s double-slit experiment < Back Next > x a D antinodal line nodal line λ D a x =

15. 15 Sound Waves Sound waves are produced by vibrating sources. They are longitudinal waves requiring a medium for propagation. It cannot travel in vacuum. Applications of reflection of sound wave: a. sonar or high frequency sound waves used to determine depth of ocean b. Ultrasonography uses ultrasound waves to examine condition of fetus , the reflected waves used to form an image on a monitor. c. Ultrasound is also used to detect tumour in the body d. Reflection of ultrasound from rocks used in geological survey . < Back Next >

16. 16 Electromagnetic Waves Common properties: a. Need no medium, can travel in vacuum . b. Travels at constant speed of light , c = 3 x 10 8 m s -1 in vacuum. c. Transverse waves. d. Wave properties like reflection, refraction, diffraction & interference. < Back Next > Radiotherapy, sterilizer Radioactive nuclei Gamma rays X-ray photography, radiotherapy, detection of cracks X-ray tube X-rays Fluorescent lamp, sterilizer, sun bed Very hot bodies, Sun, tubes Ultraviolet Photography, fibre optics Sun, lamps Visible light Heating, remote control, night vision Hot objects, Sun Infra-red Radio, radar Inductor-capacitor circuit Radio waves, microwaves Applications Sources Name