Wave Motion Science Prep.2 Lesson - PDF

Here is the converted text into a markdown format # Science Mr. Ahmed Elbasha ## Prep.2 ## Second Term ## Unit One – Lesson Two # Wave Motion Name : \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ## In this lesson, we will study: 1. The role of waves in tr...

Here is the converted text into a markdown format # Science Mr. Ahmed Elbasha ## Prep.2 ## Second Term ## Unit One – Lesson Two # Wave Motion Name : \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ## In this lesson, we will study: 1. The role of waves in transferring energy. 2. The concept of wave motion. 3. Types of waves. 4. Some concepts related to wave motion and their properties. ### ◉ The role of waves in transferring energy: #### Activity 1 Defining the concept of wave and its role in energy transfer : * **Observation:** The pieces fall one after the other, as well as they don't change their positions after falling. * **Explanation:** 1. When the first domino piece falls, it will transfer its energy to the second piece, which falls transferring its energy to the third one and so on. 2. The transfer of energy continues and the pieces do not change their positions in the row. * **Conclusion:** The disturbance that propagates and transfers energy in the direction of propagation is known as the wave. * **The wave:** It is the disturbance that propagates and transfers energy in the direction of propagation. ### ② The concept of wave motion: #### Activity 2 To conclude the concept of wave motion : * **Observation:** 1. The flame of the candle vibrates. 2. The vapor of burning incense stick does not enter the tube which indicates that air molecules do not move with the sound waves through the tube. * **Explanation:** 1. Energy is generated when the tuning fork vibrates. This energy is transferred in the form of sound waves. 2. The medium particles (air and smoke particles) vibrate without moving from their places during the propagation of sound waves, which carry energy to the candle flame. * **Conclusion:** The movement resulting from the vibration of the medium particles at a certain moment in a specific direction is known as wave motion and the direction of progression of the wave is known as the line of wave propagation. ### Wave motion: It is periodic motion produced as a result of the vibration of medium particles at a certain moment and in a definite direction ### The line of wave propagation: It is the direction through which the wave propagates. ## ③ Types of waves: Waves are classified according to * **The direction of vibration of medium particles relative to the direction of propagation into:** * Transverse waves * Longitudinal * **The ability to propagate and transfer energy into:** * Mechanical waves * Electromagnetic ### Transverse and Longitudinal waves: #### Activity 3 To show the nature of transverse and longitudinal waves : * **Observation** * The coloured tape vibrates in its place in a direction perpendicular to the direction of the vibration of rings of spring which move up and down forming crests and troughs. * The coloured tape vibrates in its place along the direction of the vibration of rings of spring which are too close to each other in some areas forming **compressions** and are faraway from each other in some areas forming **rarefactions.** * **Explanation:** If we considered that the vibration of spring represents wave propagation. * **So:** vibration of rings of spring represents the direction of wave propagation. vibration of coloured tape represents the direction of vibration of medium particles. * **Conclusion:** * During the wave propagation, the medium particles vibrate around their rest positions without transferring. * The wave at which the medium particles vibrate in a direction perpendicular to the direction of wave propagation is called transverse waves as in the first case. * The wave at which the medium particles vibrate along the direction of wave propagation is called longitudinal waves as in the second case. We can compare between transverse and longitudinal waves as follows: | | Transverse wave | Longitudinal wave | | :-------------------- | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :---------------------------------------------------------------------------------------------------------- | | | **Transverse wave:**It is a disturbance in which the particles of the medium vibrate perpendicular to the direction of wave propagation. | **Longitudinal wave:**It is a disturbance in which the particles of the medium vibrate along the direction of wave propagation. | | **Illustrating figure** | Includes a description of direction of vibration of medium particles and direction of wave propagation. | Includes a description of direction of vibration of medium particles and direction of wave propagation. | | **Formation** | includes a description of: Direction of vibration of medium particles, Crest, Direction of wave propagation, Trough.It is formed from :crests and troughs. **Crest:**It is the highest point of the particles of the medium is transverse wave. **Trough:** It is the lowest point of the particles of the medium in the transverse wave. | It is formed from :compressions and rarefactions. Compression:It is the area in the longitudinal wave at which the particles of the medium are of the highest density and pressure. Rarefaction:It is the area in the longitudinal wave at which the medium particles are of the lowest density and pressure. | ### In the wave motion curve: * The crest of the transverse wave is equivalent to the center of compression of the longitudinal wave. * The trough of the transverse wave is equivalent to the center of rarefaction of the longitudinal wave. ### Real Life application * **Idea of work** * Jacuzzi is found in most health clubs and it is a tub where water moves in the form of circular waves. * **Uses of Jacuzzi** * It is used to treat: 1. Sprains and cramps by using hot water. 2. Nervous tension by using cold water. ### Electromagnetic and mechanical waves: | Electromagnetic waves : | Mechanical waves : | | :--------------------------------------------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------- | | They are waves which do not need a medium to propagate, where they propagate through vacuum. **Types:** | They are waves which need a medium to propagate, where they do not propagate through vacuum. **Types:** | | * They are all transverse waves, such as : ** Light waves. ** Infrared waves. ** Radio waves (used in radars). | * **Transverse waves:** as water waves. * **Longitudinal waves:** as sound waves. ### Velocity of propagation * They propagate by a velocity $3 \times 10^8$ m/sec. in vacuum but their velocity decreases when they transfer in media. * They propagate with a velocity is much less than the velocity of electromagnetic waves in media. ### Radio waves are transverse electromagnetic waves. They are transverse because the particles of the medium vibrate perpendicular to the direction of wave propagation forming crests and troughs and electromagnetic because they propagate through vacuum. ### Sound waves are longitudinal mechanical waves. They are longitudinal because the particles of the medium vibrate along the direction of wave propagation forming compressions and rarefactions and mechanical because they need a medium to propagate through. #### G.R * Hearing thunder after seeing lightning although they both happen at the same time. Because the light of lightning is from electromagnetic waves, while the sound of thunder is mechanical waves, where the velocity of electromagnetic waves is much greater than the velocity of mechanical waves. * We can't hear the sound of solar explosions occurring on the Sun, but we can see the light coming out of it. Because the sound is mechanical waves, which need a medium to propagate through, while the light is electromagnetic waves, which can propagate through vacuum. ## ✔ Some concepts related to wave motion and its properties: 1. Wavelength. 2. Wave amplitude. 3. Wave velocity. 4. Wave frequency. ## 1 Wavelength ($\lambda$): ### The wavelength ($\lambda$) of the transverse wave : It is the distance between two successive crests or troughs ### The wavelength ($\lambda$) of the longitudinal wave : It is the distance between the centres of two successive compressions or rarefactions * The measuring unit of wavelength ($\lambda$) is "metre". * Laws used for determination the wavelength ($\lambda$) : | | | | :-------------------------------------- | :---------------------------------------------------------------------------------------------------------------- | | 1. Wavelength of a transverse wave | = 2 x the horizontal distance between the successive crest and trough. | | 2. Wavelength of a longitudinal wave | = 2x the distance between the centres of successive compression and rarefaction. | | 3. Wavelength | = $\frac{ The distance covered by waves}{Number of waves}$ | ## 2 Wave amplitude: It is the maximum displacement achieved by the medium particles away from their rest positions. * The measuring unit of wave amplitude is "meter". ### Law used for determination the wave amplitude: * The vertical distance between the crest and the trough of a wave = 2 $\times$ Wave amplitude Wave amplitude = $\frac{The vertical distance between the crest and the trough of a wave}{2}$ ## 3 Wave velocity (V): The velocity of the transfer of the energy carried by the wave is represented by wave velocity. ## Wave velocity (V): It is the distance covered by the wave in one second. * The measuring unit of wave velocity is "metre per second (m/s)". * Wave velocity can be determined by the relation : V = $\frac{Distance covered by the wave in meters (m)}{Time in seconds (s)}$ * Wave velocity is constant through the same medium, but it changes from one medium to another, as follows: * The velocity of sound waves through air = 340 m/s * The velocity of sound waves through water = 1500 m/s * The velocity of sound waves through wood = 1830 m/s i.e. The velocity of sound through solids $>$ The velocity of sound through liquids $>$ The velocity of sound through gases (air). ## 4 Wave frequency (F): We have learned in the first lesson, the meaning of the frequency of an oscillating (vibrating) body, now we can define the frequency of the wave as follows : ## Wave frequency : It is the number of complete waves produced from the source in one second. * The measuring unit of frequency is "Hertz". * Wave frequency can be determined by the relation : F= $\frac{Number of complete waves}{Time in seconds(s)}$ So, Periodic time of the wave (T)= $\frac{1}{Frequency (F)}$ *The periodic time of the wave is the time taken to make one wave.* ## Law of wave propagation : It is the relation between the wave velocity (V), its frequency (F) and wavelength ($\lambda$) in the wave motion. From the figure : The distance covered by the wave in one second = $\frac{Number of complete waves in one second}{* The length of a complete wave}$ Therefore, $ V =f\times \lambda$ This relation is known as the law of wave propagation and it can be applied for all types of waves. ### To calculate the wave velocity, wavelength and frequency : V = f$\times \lambda$ $\lambda = \frac{V}{f}$ $f=\frac{V}{\lambda}$ ### Notice that * Frequency (F) is inversely proportional to wavelength ($\lambda$) in the same medium. * Wave velocity (V) is directly proportional to frequency (F) at constant wavelength ($\lambda$). * Wave velocity (V) is directly proportional to wavelength ($\lambda$) at constant frequency (F).