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Introduction to Waves Auto slide change for this page, WAIT…..

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2 Introduction to Waves Auto slide change for this page, WAIT…..

3 Part A : Definition - Definition of waves. - Basic Properties of waves. Part B : Types of Waves and Terminology. - Mechanical waves : Transverse and Longitudinal waves. - Electromagnetic waves. - Terminology of waves. Part C : The Wave Equation. Part D : Common Characteristic of Waves. Part E : Revision The basics

4 PART A Definition of wave PART A Definition of wave A periodic disturbance which travels through a medium from one point in space to the others. Wave motion means the propagation of waves through a medium. Wave motion appears in almost every branch of Physics.

5 Basic properties of waves Basic properties of waves : Energy is transferred from one place to another in a wave motion. Motion of the medium (particles of the medium) is usually periodically vibratory. Only the shape or form of wave travels, not the medium. Remember to take notes

6 PART B TYPES OF WAVES Waves PART B TYPES OF WAVES Waves are classified into different types according to their natures :

7 1. Mechanical Waves A material medium is necessary for the transmission for mechanical waves. Mechanical waves cannot travel through vacuum. Due to elastic forces on adjacent layers of medium, disturbance is transmitted from one layer to the next through the medium. according to the direction of vibration, waves are also classified into : (a) Transverse wave; (b) Longitudinal waves. click And... Click for examples Water waves, sound, vibration of spring, etc.

8 Transverse Waves 1.1 Transverse Waves The waveform appears in the shape of sine curve. A wave in which the motions of the matter particles are perpendicular to the direction of propagation of the wave itself. Water waves, pulse in a stretched string,transverse wave demonstrator. Examples

9 Longitudinal Waves 1.2 Longitudinal Waves A wave in which the motions of the matter particles are in the same direction as the wave propagation. Examples Sound, or a spring oscillating up and down, etc.Show magnetic longitudinal demonstrator

10 2. Electromagnetic Waves Material medium is not essential for propagation. e/m waves travel through vacuum. Disturbance of electric and magnetic fields travelling through space. All electromagnetic waves are transverse waves. X-rays, radio waves, micro-waves,etc. examples

11 Terminology of a Wave Amplitude Wavelength ( ) Frequency (f) Period (T) Wave velocity (v) A wave is usually described by the following terms : Each term will be explained….

12 The amplitude is the maximum displacement of the medium from its equilibrium position. The wavelength ( ) is the minimum distance between two points which are in phase. The frequency (ƒ) is the number of complete oscillations made in one second. Unit : Hz The period (T) is the time taken for one complete oscillation. It is related to frequency by T = 1/ƒ Unit : s Table of Contents

13 The Wave Equation The wave velocity is the displacement traveled by the wave in one second …….... The wave velocity (v) is related to frequency and wavelength by -- v = ƒ The Wave Equation PART C Click to explore

14 Using the Wave Equation Using the Wave Equation Example : A travelling wave of wavelength 0.6m moves at a speed of 3.0 m/s. What is the period of this wave ? Click to see the answer Then the period of this wave is ??? Period T = 1/ƒ T = 1/5.0 or 0.2 s Now you know = 0.6 m, v = 3.0 m/s Can you find the frequency of this wave…… Table of Contents By using the wave equation, v = ƒ 3.0 = ƒ(0.6) i.e ƒ = 5.0 Hz

15 Transmission of energyTransmission of energy ReflectionReflection RefractionRefraction DiffractionDiffraction InterferenceInterference Click to see PART D

16 Let ’ s take water waves as an example to study the characteristics of waves…. The behavior of water waves demonstrates all these characteristics…….. characteristics

17 Reflection of Waves reflected A travelling wave is reflected when it hits a barrier. This phenomenon can easily be observed when a travelling water wave hits a reflector in the ripple tank. Reflection of Waves Reflected waves Reflecto r

18 Refraction of Waves refraction - The speed of a water wave increases with depth. This change in speed is accompanied by refraction. This effect is a consequence of the wave equation, v = ƒ. Since ƒ is constant, a decrease in v produces a decrease in.

19 Diffraction of Waves. When a travelling water wave hits an obstacle, the wavefronts spreads out round the edge and becomes curved. This phenomenon refers to diffraction. The wavelength of the wave is not changed in diffraction.

20 Interference of Waves interference When two or more waves propagating in the same medium meet at the same point, interference is said to occur. A stable interference pattern can be observed when two water waves of same frequency meet one another in a ripple tank. + = Click for example

21 We have seen that mechanical waves (water waves in our example) well demonstrate these characteristics. Electromagnetic waves show all these characteristics as well. It is known that light demonstrates all these five characteristics of waves, do you think that light exists in the form of wave ? it is an electromagnetic wave. Think Click for answer All kinds of waves demonstrate these 5 characteristics All kinds of waves demonstrate these 5 characteristics. Yes --

22 PART E After this lecture, you should be able to answer the following questions : Now you have learned the basic Waves concepts of Waves. Are you ready ? Click here to go back to table of contents --> Next page End the slide show

23 1. What is the difference between mechanical and electromagnetic waves ? 2. Can you give some examples of electromagnetic waves ? 3. What is the direction of the particle motion in a transverse wave ? 4. Is sound a transverse or longitudinal wave ? More questions 5. Is it correct that water waves do not transmit energy from one point to another ? If you do not have all 5 questions answered correctly, click here and back to part B again if necessary ---->>

24 1. In a wave diagram, can you identify the following terms ? (a) wavelength (b) amplitude. 2. Write down the wave equation. 3. What are the 5 common characteristics of waves ? If you miss any of this questions, go back to the lesson by clicking this button -->>

25 Now we come to the conclusion of introducing waves. You should be able to tell the nature of waves, and identify different types of waves after this lecture. The study of waves is important in Physics. From the motion of water to the structure of atoms, study of waves applies almost in every category. THE END OF LECTURE

26 Constructive Interference

27 Destructive Interference

28 Reflected Waves

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