1. Waves and Energy Transfer
AP Physics
Waves and Energy Transfer

2. TEKS Objective: 8A
The student knows the characteristics and behavior of waves. The student is expected to:
(A) Examine and describe waves propagated in various types of media and describe wave characteristics such as velocity, frequency, amplitude, and behaviors such as reflection, refraction, and interference.

3. Two Main Topics
Wave properties
Wave behavior

4. Waves transfer energy
A wave pulse is a single disturbance
A repeated disturbance is a continuous wave pattern

5. Wave properties
Mechanical Waves – transfer energy, require a medium and obey Newton’s Laws of Motion
What is a medium?
Sound waves – called compressional or longitudinal waves
Transverse wave – move through the medium, making an “s” shape

6. 2. Measuring Waves Speed – how fast the wave is moving Unit: m/s
Formula:

7. 2. Measuring waves continued:
Amplitude – maximum displacement from equilibrium
Wavelength – the distance need to make one complete cycle or wave, usually measured from crest to crest (λ), usually measured in meters.

8. 2. Measuring waves continued:
Period – the time needed to make one complete wave or cycle
(T) unit is usually the second
Frequency – the number of waves or cycles in a time unit (usually one second)
(f) Unit is the Hertz (Hz)

9. 2. Measuring Waves continued:
Period and frequency have an inverse relationship

10. 3. Parts of a Wave Crest – highest point of a wave
Trough – lowest point of a wave
Amplitude – maximum displacement from line of equilibrium
Wavelength – λ the distance needed to complete one wave or cycle

11. Parts of a Transverse Wave

12. 4. Two types of waves:
Transverse – particles vibrate perpendicular to the direction of the wave motion

13. Longitudinal or compressional – particles vibrate parallel to the direction the wave motion. Examples: sound waves, primary earthquake waves

15. Example Problem
A sound wave has a frequency of 262 Hz and a wavelength of 1.29 m.
What is the speed of the wave?
How long will it take the wave to travel the length of a football field (91.4m)?
What is the period of the wave?

16. Homework
Page 335 #1-7

17. Wave Behavior When waves interact with boundaries they can: Reflect
Refract
Diffract
Interfere

18. Reflection
Is when a wave bounces back off a boundary or barrier

20. Parts of Reflection
Normal – the imaginary line perpendicular to the barrier at the point of reflection
Angle of incidence – angle between the incident ray and the normal
Angle of reflection – angle between the normal and the reflected ray

21. Parts of reflection continued:
Law of Reflection – for a smooth surface, the angle of incidence equal the angle of reflection

28. Refraction
Bending of a wave at the boundary between two media as the wave moves from one medium to another, velocity and wavelength change, but period and frequency remain constant

31. Diffraction Waves moving around a barrier. Examples: sunset, mirage

32. Diffraction continued:

33. Interference
The superposition of waves, waves pass through each other unchanged, it is only a displacement of matter

34. Two types: Constructive and Destructive interference

35. Constructive Interference
When two waves combine to produce a wave with a larger amplitude, the meet crest to crest

38. Destructive Interference
When two waves combine to produce a wave with a smaller amplitude, they meet crest to trough

39. Total destructive interference

40. Standing Waves When two waves meet with equal and opposite amplitudes
Parts of a standing wave: node and antinode
Node is the area of no apparent motion
Antinode is the area of maximum displacement

44. Homework
Page 337 #8-10
Review problems page 346 #32-47