1 Wave Behavior Physics: Chapter 14 Section 2 Mrs. Warren

Let us Recap Shall We? Parts of Wave Types of Waves Frequency Velocity Period 2

3 Waves are everywhere in nature Sound waves, visible light waves, radio waves, microwaves, water waves, sine waves, telephone chord waves, stadium waves, earthquake waves, waves on a string, slinky waves

4 Wave Behavior Now we know all about waves. How to describe them, measure them and analyze them. But how do they interact?

5 Wave Behavior We know that waves travel through mediums. But what happens when that medium runs out?

6 Boundary Behavior The behavior of a wave when it reaches the end of its medium is called the wave’s BOUNDARY BEHAVIOR. When one medium ends and another begins, that is called a boundary. The speed of a mechanical wave depends only on the properties of the medium it passes through.

7 Fixed End One type of boundary that a wave may encounter is that it may be attached to a fixed end. In this case, the end of the medium will not be able to move. What is going to happen if a wave pulse goes down this string and encounters the fixed end?

8 Fixed End Here the incident pulse is an upward pulse. The incident pulse is a wave that strikes the boundary. The energy that the incident pulse has when it reaches the boundary has to be REFLECTED. Why?

9 Fixed End In this instance, the reflected pulse is upside-down. It is inverted. The reflected pulse has the same speed, wavelength, and amplitude as the incident pulse. The reflected pulse can be upward or downward (inverted)…this will depend upon the thickness of the medium and the boundary situation.

10 Free End Another boundary type is when a wave’s medium is attached to a stationary object as a free end. In this situation, the end of the medium is allowed to slide up and down. What would happen in this case?

11 Free End Here the reflected pulse is not inverted. It is identical to the incident pulse, except it is moving in the opposite direction. The speed, wavelength, and amplitude are the same as the incident pulse.

Examples of Reflected Waves Two types of Reflected Waves Two types of Reflected Waves The picture to the right is an example of an incident wave reflecting upwardly from its boundary. 12

Junction of Two Springs 13

14 Change in Medium Our third boundary condition is when the medium of a wave changes. [There are 2 types] Think of a thin rope attached to a thicker rope. The point where the two ropes are attached is the boundary. At this point, a wave pulse will transfer from one medium to another. What will happen here?

15 Change in Medium In this situation part of the wave is reflected, and part of the wave is transmitted. Part of the wave energy is transferred to the more dense medium, and part is reflected. The transmitted pulse is upright, while the reflected pulse is inverted.

16 Change in Medium The speed and wavelength of the reflected wave remain the same, but the amplitude decreases. The speed, wavelength, and amplitude of the transmitted pulse are all smaller than in the incident pulse.

Change in Medium What happens to the pulses when energy is transferred from a more dense medium to a less dense medium? What happens to the speed, wavelength, and amplitude of the transmitted pulse? What happens to the speed, wavelength, and amplitude of the reflected pulse? 17

18 Wave Interaction Suppose a pulse traveling down a spring meets a reflected pulse coming back. In this case, 2 waves exist in the same place in the medium at the same time. Principle of Superposition

19 Constructive Interference When two waves meet while traveling along the same medium it is called INTERFERENCE. [This is a result of superposition of 2 or more waves] Let’s consider two waves moving towards each other, both having a positive upward amplitude. What will happen when they meet?

20 Constructive Interference They will ADD together to produce a greater amplitude. This is known as CONSTRUCTIVE INTERFERENCE.

21 Destructive Interference Now let’s consider the opposite, two waves moving towards each other, one having a positive (upward) and one a negative (downward) amplitude. What will happen when they meet?

22 Destructive Interference This time when they add together they will produce a smaller amplitude. This is know as DESTRUCTIVE INTERFERENCE.

23 Check Your Understanding Which points will produce constructive interference and which will produce destructive interference? Constructive G, J, M, N Destructive H, I, K, L, O

Continuous Waves 24

Continuous Waves 25

Standing Waves What is a standing wave? A wave that appears to be standing still. Generating a wave, but the wave doesn't propagate. Examples: Vibrating a string or cord. Standing Wave vs. Moving Wave We need to look at what a node and antinode are. 26

Standing Waves 27

Standing Wave Examples 28

Problem 29

Solution 30

Waves in 2 Dimensions Behavior of waves on a rope or string. 1 dimensional But what if the wave is traveling in a two- dimensional medium? Or what if the wave is traveling in a three-dimensional medium? What types of behaviors can be expected of these waves? 31

Reflection in 2-D Waves 32

Law of Reflection 33

Law of Reflection 34

Refraction Reflection involves a change in direction of waves when they bounce off a barrier. Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. 35

Refraction 36

Comparing Reflection and Refraction 37

Diffraction If particles are thrown at a barrier with holes, the particles will either reflect off the barrier or pass straight through the holes. However, they do not pass straight through. What happens? 38

Diffraction The spreading of waves around the edge of a barrier is called diffraction. A more scientific definition: Diffraction refers to various phenomena which occur when a wave encounters an obstacle. 39

Diffraction 40

Diffraction What happens when you have two slits for water or another medium to pass through? 41

Diffraction 42

Diffraction 43