bac1-lebanon-ch1-Vibrations and waves.pptx

This is a physics course for grade 11 Scientific section in lebanese curriculum, chapter 1: waves and Vibrations

1. Waves Grade 11 Sc | Chapter 1

2. Objectives: After watching this video, the student should be able to: Distinguish between a vibration and a wave. Know that waves transport energy but not matter. Know the characteristics of a traveling wave. Distinguish between mechanical and electromagnetic waves. Hussein H. Harb

3. 1.1. Periodic Motion Is a motion that repeats itself every constant interval of time called period. Hussein H. Harb

4. 1.2. Vibrations Vibrations or oscillations are regular to-and-fro motions of an object between two extreme positions. to fro Extreme position Extreme position to fro Extreme position Extreme position Hussein H. Harb

5. 1.3. Characteristics of a vibration Time for 10 oscillations=20.2s  Time for one oscillation=2.02s and It is constant. Hussein H. Harb

6. 1. Period Symbol: Unit in SI: Definition: Expression: Seconds [s] is the constant interval of time a vibrating object takes to make one vibration.     1 oscillation  T N oscillations  t Hussein H. Harb

7. 2. Frequency Symbol: Unit in SI: Definition: Expression:     Is the number of oscillations a vibrating object completes in one second.   N oscillations  t f  1 sec Thus, is the inverse of :     Hussein H. Harb

8. 3 . Amplitude Symbol: Unit in SI: Definition: or or   Meters [m] or degrees [ ]   is the maximum displacement of the vibrating object in either direction measured from the equilibrium position . Equilibrium position     Extreme position Extreme position     Equilibrium position Extreme position Extreme position Hussein H. Harb

9. 4. Average Speed Symbol: Unit in SI: Expression:   m/s   Hussein H. Harb

10. App 1.1 . 20 cm 40 oscillations in 20 seconds a=? f =? T =?   The amplitude is equal to half of the described segment : The frequency is the ratio of the number of cycles and the time taken : The period is the inverse of the frequency :       Hussein H. Harb  

11. 1.4. Progressive Waves In the first case, the traveling hump is called a signal or a pulse . In the second case, the series of traveling humps is called a wave train , or simply a wave .

12. Properties: To produce waves , we need a source of vibrations. The source causes disturbances in the medium, which travel away from the source, progressing from point to point in the medium . This is called a traveling or progressive wave . The particles of the medium do not propagate from point to point as the wave does but oscillate around their equilibrium positions. This means that, while it propagates, a progressive wave transports energy but does not transport matter . Hussein H. Harb

13. 1.5. Characteristics of a wave Period Frequency Amplitude (same as mentioned before) Hussein H. Harb

14. 4. Wavelength Symbol: Unit in SI: Definition: is the distance traveled during a period T of the vibrating source   Meters [m]             Hussein H. Harb

15. 5. Speed of propagation Symbol: Unit in SI: Definition: Expression:   Meters per seconds [m/s] Is the distance covered by the wave per a time interval In a homogeneous medium, a traveling wave has a constant speed of propagation Thus,   But   Then,     Hussein H. Harb

16. Application 1.2 . 5.4 m         Hussein H. Harb

17. App 1.3 . 15cm               Hussein H. Harb

18. 1.6. Types of waves displacement of particles is perpendicular to the direction of propagation of wave. displacement of particles is parallel to the propagation of wave. transverse longitudinal Direction of propagation displacement of particles displacement of particles Hussein H. Harb

19. App 1.4 . Transverse or longitudinal? Hussein H. Harb

20. 1.7. Electromagnetic waves Whenever an electron falls from an energy level to a lower one , it emits an electromagnetic wave. In general, when charges oscillate , electromagnetic waves are produced . These waves, unlike mechanical waves, do not need a material medium to propagate: they can travel in vacuum . T heir speed is always the same , equal to c = 300000km/s = 3xl0 8 m/s in vacuum. It is different in other mediums. For electromagnetic waves in vacuum, . Electromagnetic waves are transverse waves.   Hussein H. Harb

21. (3.75x10 14 Hz) (7.5x10 14 Hz) Electromagnetic waves differ by their frequencies Increasing frequency Hussein H. Harb

22. App 1.5 . Give two differences between Mechanical waves and Electromagnetic waves Mechanical waves Electromagnetic waves Need a material medium to propagate. Do not need a material medium to propagate: they can travel in vacuum. Could be transverse or longitudinal. They are transverse waves. Hussein H. Harb