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Waves. Activity  In your notebook, make a list of some things you know about waves. Include examples of waves, and any terms that you know that apply.

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Presentation on theme: "Waves. Activity  In your notebook, make a list of some things you know about waves. Include examples of waves, and any terms that you know that apply."— Presentation transcript:

1 Waves

2 Activity  In your notebook, make a list of some things you know about waves. Include examples of waves, and any terms that you know that apply to waves.

3 Waves  Waves are repeated disturbances that move along in a certain direction.

4 Wave Motion  Below is a picture of water waves. What is the direction of motion for water waves?

5 Wave Motion  Water waves travel in a horizontal direction. The parts of the waves that travel in a horizontal direction are called the wavefronts. Wavefronts

6 Wave Motion  If you are floating in water, what is your direction of motion?  Objects floating in water move in a vertical direction as the wavefronts pass by.

7 Measuring Waves  The highest point of a wave is called the crest or the peak.  The lowest point is called the trough. crest or peak trough

8 Measuring Waves  Speed – the distance traveled by a crest or a trough every second.  Symbol – v  Unit – meters/second or m/s v

9 Measuring Waves  Speed – the distance traveled by a crest or a trough every second.  The speed of sound in air is 340m/s. The speed of light in a vacuum is 300,000,000m/s. v

10 Measuring Waves  Wavelength – the distance from one wave crest to the next.  Symbol – λ(Greek letter pronounced “lambda”)  Unit – meters or m (or in cm, mm, or nm) wavelength

11 Measuring Waves  Amplitude – the height of the wave crest from the middle.  Symbol – none  Unit – meters or m (or in cm, mm, or nm) amplitude

12 Measuring Waves  Frequency – the amount of complete waves passing a point in one second.  Symbol – f  Unit – hertz (Hz)

13 The Wave Equation  speed = frequency x wavelength v = fλ  v – the speed of the wave in m/s  f – the frequency of the wave in Hz  λ – the wavelength of the wave in m

14 Summary Tasks  Copy Figure from your textbook on page 105.  Use the glossary of your textbook and write the definitions for the following key words: wavefront, frequency, wavelength, and amplitude.  Answer questions 1 and 2 on page 105.

15 Transverse and Longitudinal Waves

16 Transverse Waves  Recall that the direction a wave is moving is the direction the wavefront is traveling.  In transverse waves the vibrations are perpendicular to the direction in which the waves are traveling.

17 Polarised Waves  Transverse waves are polarised if the vibrations are always along the same line.  The following diagram shows two different polarised waves.

18 Polarised Waves  If we use an object that only allows one direction of wave to pass through, we can turn unpolarised waves into polarised waves.

19 Polarised Waves  Light waves from a lamp are unpolarised transverse waves.  A Polaroid material only allows light waves that vibrate in the same direction.

20 Polarised Waves  If a second Polaroid filter is place at a right angle to the first one, the polarised waves will not be able to pass the second one.

21 Longitudinal Waves  The vibrations of a longitudinal wave are parallel to the direction in which the waves are traveling.  Sound waves are created when an object vibrates. The vibration repeatedly pushes and pulls the air. As each layer of air

22 Comparing Transverse and Longitudinal Waves  On transverse waves the high point is the crest and the low point is the trough.  On longitudinal waves, the high density point is called a compression and the low density point is a rarefaction.

23 Summary  Transverse waves vibrate at right angles to the direction of travel of the waves.  Longitudinal waves vibrate parallel to the direction of travel of the waves.  Light waves and waves on a rope are transverse waves.  Sound waves are longitudinal.  Transverse waves are polarised if the vibrations are always along the same line.  Pg. 107 #1,2

24 Reflection and Refraction

25 Reflection  Waves travelling towards a barrier will be reflected. The waves moving towards the barrier are called incident waves and the waves travelling away are called reflected waves.  The reflected waves are at the same angle from the barrier as the incident waves.

26 Reflection

27 Refraction  Refraction occurs when  Waves change from one medium to another, which changes the speed  The waves approach the barrier at a non- zero angle

28 Refraction

29 Diffraction

30  Diffraction is the spreading of waves when they pass through a gap or move past an obstacle.

31 Gap Size  A narrow gap makes the wave spread out more.  A wider gap makes the waves spread out less.

32 Note:  For diffraction to be noticeable the gap must be similar in width to the wavelength of the waves.  The wavelength does not change when diffraction occurs.

33 Summary  Diffraction is the spreading of waves when they pass through a gap or round an obstacle. For noticeable diffraction the gap must be similar in size to the wavelength.  The wavelength does not change on diffraction.  The narrower the gap, the more the waves spread out.


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