Waves

 

 

Resources: The Physics Classroom; http://www.phy.ntnu.edu

 

8.1 Waves

a. Describe transverse and longitudinal waves
b. Compare the characteristics of sound, light and seismic waves (e.g., transverse/longitudinal, travel through various media, relative speed)
c. Explain that energy is transferred by waves without mass transfer and provide examples
d. Diagram the relative positions in the electromagnetic spectrum of radio, microwave, infrared, visible spectrum, ultraviolet and X-rays This has already been accomplished under section b). It need not be repeated.
e. Explain how lenses are used in simple optical systems, including the camera, telescope, microscope, and the eye
f. Explain and apply the laws of reflection and refraction
g. Calculate quantities involving wavelength, wave speed, and frequency
i. Explain the Doppler effect and provide examples

 

 

Study all animations carefully

Describe transverse and longitudinal waves

Waves and wavelike motions

What is a wave?

Categories of waves

PROPERTIES OF WAVES

Anatomy of waves

Frequency and period of a wave

Energy transport and amplitude of a wave

Speed of a wave

The wave equation

 

 

Compare the characteristics of sound, light and seismic waves (e.g., transverse/longitudinal, travel through various media, relative speed)

P and S Wave Animations- Earthquakes

Details about P, S, Love and Rayleigh waves - EARTHQUAKES: Click on View and Text Size and increase the size of the text to be able to distinguish it from its background.

Electromagnetic Waves

Description of Electromagnetic Waves

Regions of the Electromagnetic Spectrum

 

SOUND WAVES

OCEAN WAVES

SOUND PROPERTIES AND THEIR PERCEPTION

BEHAVIOR OF WAVES

Reflection, refraction and diffraction-1 Applications of activities 1 and 2 are found in the activities below:

Reflection, refraction and diffraction-2

STANDING WAVES

 

 

Explain that energy is transferred by waves without mass transfer and provide examples

All waves move through the air, water, and land as energy waves. The individual molecules of the different media do not move. This is shown in the section above. The only exception are electromagnetic waves that have the capability of transferring energy through the vacuum of outer space (without a medium).

 

 

Explain how lenses are used in simple optical systems, including the camera, telescope, microscope, and the eye

How do we know light behaves as a wave?

Wavelike behaviors of light

Interference

Interference using water waves

Movie

Interference using laser light

ACTIVITIES

Superposition of two wave pulses

What is constructive interference and destructive interference when two waves are transmitted through a medium?

1. When you open the link above, you will see two blue wave pulses approaching each other. As they get close to each other put the mouse arrow over the right wave pulse and push the left mouse button down and hold it down (DON'T LET IT GO). Then slowly drag the right pulse to the left. When the pulse begins to pass through the other a black line will appear to show how putting two identical waves on top of each other will affect the wave. NOTE WHAT HAPPENS. Continue dragging the left wave until it completely passes through the other wave.

2. Reset the waves by double right clicking on the java applet. Then click underneath the right wave so it will switch the right wave pulse to the bottom of the string or spring.. Again, put the mouse arrow under the right wave pulse and when it gets close to the pulse coming from the other direction, push down on the mouse button and don't let go. IN YOUR MIND PREDICT WHAT WILL HAPPEN TO THE BLACK LINE REPRESENTING THE RESULT OF THE MIXTURE OF THE TWO WAVES AS they pass through each other. Now watch carefully what happens to the black line as the waves pass through each other.

3. Answer the following questions AS PART OF THE FIRST PART OF THE ACTIVITY: a) What is destructive interference and which of the trials (1 or 2) represents this kind of behavior for waves. b) What is constructive interference and which of the trials (1 or 2) represents this kind of behavior for waves?

4. An example of destructive interference comes when you are listening to a radio station and are near mountains. The radio signal disappears and then reappears once again. For EXTRA CREDIT, predict from what you now know WHY THIS KIND OF INTERFERENCE HAPPENS.

Superposition of MULTIPLE waves

  • SECOND HALF OF SUPERPOSITION ACTIVITY

1. When you open the link above MULTIPLE waves will be approaching each other, blue ones from the left and black ones from the right. The waves that appear as a result of their superposition WILL BE RED IN COLOR. As the waves pass through each other left mouse click until you can see what is happening to the SUPERIMPOSED waves (red line) as compared to the position of the red and blue waves. DESCRIBE WHAT YOU SEE.

2. COMPLETE THE SUPERPOSITION REPORT BY DESCRIBING YOUR FINDINGS in 1) in terms of constructive and destructive interference. Your lab for this unit deals with this phenomena.

 

Color and Vision

ACTIVITIES

Review: Electromagnetic Spectrum

Dispersion: The spreading of white light into its individual colors through refraction of the different colors of light. (Done through a prism, raindrops, ornate window glass.)

Light absorption, reflection and transmission

Color addition

Color by Addition Activity

1. When you open the link above, you will see three circles or ovals of colors of red, blue and green LIGHT If your background is NOT already black, double right click the mouse and the black background will appear. This means you are in the applet simulating visible light.)

2. Place the mouse pointer in each color alone and look up at the red, blue and green boxes (THESE BOXES REPORT WHICH OF THE COLORS WE ARE SEEING WITH OUR EYES [255]AND WHICH COLOR WE ARE NOT SEEING [0]) and write down what color the circle/oval is and what color of light is entering our eyes AND WHICH COLOR(S) IS/ARE NOT ENTERING OUR EYES. (255 means entering and 0 means not enterring.) You will need to write it down in table form so you can have a record of your learning or so you can hand it to your instructor when you are completed all of the activities.

3. Now, drag the three colors so that in the middle you see all three colors mixed and outside of the center you see the result of the mixture in combinations of two. Place the mouse into the mixture of the three at the center, the combinations of colors mixed outside of that... and in the individual colors outside of that. Record the COLOR YOU SEE IN EACH AREA AND WHICH OF THE COLORS IN EACH AREA ARE ENTERING YOUR EYES (255) AND WHICH ARE NOT ENTERING YOUR EYES (0).

4. Answer the following question: Why is the mixing of LIGHT considered to be "color by addition? To help you look at the result of the mixture of all three colors of visible light."

 

Color subtraction

Color by Subtraction Activity - If you see a white backgoround after opening the link above, you are in the pigments section. The three colored circles are magenta, purple and yellow. If it is a black background then double click right mouse button and a WHITE background will appear.

1. Drag the three ovals together so that in the middle you have the mixture of all three of the pigments and in the combinations of two outside that and in the single colors outside that (THESE BOXES REPORT WHICH OF THE COLORS FROM REFLECTED LIGHT ARE ENTERING OUR EYES [255] AND WHICH COLORS OF REFLECTED LIGHT ARE NOT ENTERING OUR EYES[0]). Write down what color each circle/oval is and what color of light is entering our eyes (255) from the pigments AND WHICH COLOR(S) OF REFLECTED LIGHT IS/ARE NOT ENTERING OUR EYES (0). You will need to write it down in a new table of the report entitled COLOR SUBTRACTION.

2. Answer the following question: Why is the mixing of pigments of colored paint considered to be "color by SUBTRACTION? You might look at the result of the three colors being added together to help you. "

Polarization

 

Blue skies and red sunsets

 

 

Reflection and its importance

Role of light in seeing

Line of sight

The Law of Reflection

Reflection:

Activity:

1. When you open the link above you will see a wave model of light that both reflects and refracts. We will concentrate on the refraction to learn important properties of waves and the media they travel through.

2. Click on "Light from air to water" in the drop-down menu and write down the index of refraction to the right. The 1.33 means that the glass is denser than the air. Measure the speed in terms of cm/s (on the screen) of the wave in air and the wave after it refracts into the glass. (You will enter this in a table you construct to record your results. Be sure you clearly label all columns and rows and don't forget titles to all your tables).

3. Click on "Light from air to diamond", record the refractive index and measure the speed in air and in diamond. Record your values

4. Click on "Same Index of Refraction" and record the refractive index. Measure the speed in medium 1 and in medium 2, both of which have the same density.

5. Divide the speed in air by the speed in a) water, b) in diamond and c) in the same medium. Compare the ratio in each media to the actual refractive index your recorded. Answer the following questions: a) Define Refractive Index in terms of this activity b) What will happen to a wave going from a more dense to a less dense medium? In comparison to the angle that it hits the media boundary, will the wave bend away from the normal at the boundary of the less dense medium or toward the normal of the less dense medium? c) WHY WILL IT DO THIS? Think in terms of speed.

 

 

Specular vs diffuse reflection

 

Refraction and the wave model of light.-refraction at a boundary

Refraction at a boundary

Cause of refraction

Refraction:

Activity:

1. When you open the link above you will see a wave model of light that both reflects and refracts. We will concentrate on the refraction to learn important properties of waves and the media they travel through.

2. Click on "Light from air to water" in the drop-down menu and write down the index of refraction to the right. The 1.33 means that the glass is denser than the air. Measure the speed in terms of cm/s (on the screen) of the wave in air and the wave after it refracts into the glass.

3. Click on "Light from air to diamond", record the refractive index and measure the speed in air and in diamond. Record your values

4. Click on "Same Index of Refraction" and record the refractive index. Measure the speed in medium 1 and in medium 2, both of which have the same density.

5. Answer the following questions: Divide the speed of the wave in light in air by a) the speed in glass, b) diamond and c) same medium. Compare the ratio of the speed in light/speed in the second medium to the ACTUAL indices of refraction and define index of refraction in terms of what you have just learned. b) What will happen to a wave going from a more dense to a less dense medium? In comparison to the angle that it hits the media boundary, will the wave bend away from the normal at the boundary of the less dense medium or toward the normal of the less dense medium? c) WHY WILL IT DO THIS? Think in terms of speed.

Optical density and light speed

Direction of bending

Secrets of Archer Fish

 

 

The mathematics of refraction

Angle of refraction

Snells Law

Problem solving

Determination of values of "n"

 

Characteristics of waves transmitted through different media

 

Image formation in plane mirrors

Why is an image formed?

Image characteristics

Activity- plane mirrors:

When the link above is opened you will see a convex lens. In order to transform it into a plane mirror, select the box that says "lens" and choose "mirror". A concave mirror will appear. Put the mouse on the top of the concave mirror and hold down the left mouse button. Drag the mirror to the right until it forms a plane mirror. Release the mouse button. The shape of the mirror will become concave but the object and image will behave as if it were a plane mirror.

1. Determine where the image is located compared to the object (OBJECTS ARE THE BLUE ARROWS IN ALL ACTIVITIES), if the image is right-side up or upside down compared to the object, whether it is a real or virtual image and what happens to the image when you move the object toward and away from the mirror (as the object distance to toward the mirror decreases, what happens to the image distance from the mirror). Finally, what happens to the image when the object size is decreased and goes below the line. Record your observations.

Ray diagrams

What part of a mirror is required to see image?

Right angle mirrors

Other multiple mirror systems

 

Concave mirrors

Structure of a curved mirror

Reflection of light and image formation

Two rules of concave mirrors

Ray diagrams: concave mirrors

Image characteristics for concave mirrors

Activity: Concave Mirrors

When the link above is opened you will see a convex lens. In order to transform it into a concave mirror, select the box that says "lens" and choose "mirror". A concave mirror will appear.

1. Using a concave mirror, make drawings of the object and image when the object is inside the focal point (R/2 or f), outside the focal point but less than R (Radius of curvature) and outside R.

 

Mirror equation: Concave mirrors

Spherical aberrations

 

Convex mirrors

Reflection and image formation: Convex mirrors

Ray diagrams: Convex mirrors

Image characteristics: Convex mirrors

Activity: Convex Mirrors

When the link above is opened you will see a convex lens. In order to transform it into a convex mirror, select the box that says "lens" and choose "mirror". Click on the + sign above the mirror (to the left of the 10.0) and the mirror changes to a diverging or convex mirror.

1. Determine where the image is located compared to the object (object is blue arrow), and make drawings of the object and image when the object is inside the focal point (R/2 or f), outside the focal point but less than R (Radius of curvature) and outside R..

 

Mirror equation: Convex mirrors

 

Total Internal Reflection

Boundary behavior

Total internal reflection

The critical angle

Activity- Critical Angle

1. Define critical angle

Describe HOW you knew when you reached the critical angle (you will know this when you begin to move the flashlight to different angles.

 

Image formation of lenses

Structure of a lens

Refraction by lenses

Image formation

Activity: Lenses

1. Convex lenses

When you open the link above you will see a convex (converging) lens. Use this lens for this activity.

Activity: Determine where the image is located compared to the object (object is blue arrow), and make drawings of the object and image when the object is inside the focal point (R/2 or f), outside the focal point but less than R (Radius of curvature) and outside R.

2. Concave lenses

Click on the + above the lens (to the left of the number 10.0 and the lens will change to a concave (diverging) lens.

Activity: Determine where the image is located compared to the object, and make drawings of the object and image when the object is inside the focal point (R/2 or f), outside the focal point but less than R (Radius of curvature) and outside R.

Ray diagrams

Object/image relationships

Diverging lenses: Ray diagrams

Object image relationships

Mathematics of lenses

 

The Eye

Structure of an eye

Image formation and detection

Accommodation

Far-sightedness/correction

Near-sightedness/correction

 

CAMERA

How a camera works

 

TELESCOPE

How a telescope works

 

MICROSCOPE

How a microscope works

 

 

 

Explain the Doppler effect and provide examples

The Doppler Effect

Doppler effect and shock waves

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Why does breaking the sound barrier (as a jet aircraft moves beyond the speed of sound) look like the picture below?

Moving point source Beginning to understand what happens(Doppler effect/sound waves)

Instructions:

  • When the new window opens, click on the animation to stop the motion and then drag the arrowhead of the "SOURCE speed" from 40 to 20 m/s. When you release the mouse-click, the animation starts on its own.
  • Observe (measure) the wavelength of the waves behind the moving point source and ahead of it. (Do this by clicking on the animation to stop it) There is a built in "measuring stick" if you wish to use it. Otherwise, use a cm ruler on the monitor. The measurments need to be as exact as possible.
  • Drag the SOURCE speed arrowhead to the right to a speed to 30 , then 40 , then 50, then 60, then 70 m/s and make corresponding measurements of the wavelengths ahead of and behind the point source. Graph the relationship between speed (the factor that changes) and the before and ahead wavelengths. Once you have done that, tell why the sound the motor of a fast moving car is high pitched when it is approaching you and low pitched after it has passed you. This is the Doppler Effect.
  • Next, increase the SOURCE speed in increments of 2 through 88 m/s (72, 74, 76, and so on) and focus on what happens to the waves in front of the moving point source.
  • Put the SOURCE speed at 100 m/s and describe what happens to the moving point source.
  • Finally answer why the jet aircraft above looks like it does as it "breaks" (moves through) the sound barrier.

Supersonic Jet Aircraft If the point source now becomes a supersonic jet aircraft, and if we had no ability to see it (example: we were blind or there was a cloud cover) Under these conditions, we need to answer where the jet is located ONCE WE HEAR ITS SOUND. You will be testing different speeds...both below, at and above the speed of sound? This activity will help you answer those questions.

Instructions
When the new window opens, check to make sure the ratio of the airplane speed to the speed of sound is 0.5 (or in otherwords, that the airplane is traveling at half the speed of sound.) Then click reset and start.
  • You will note that an airplane begins to fly from left to right (you are standing towards the same direction the plane is travelling...so it is approaching you from behind).When the blue lines appear at your ear... that is when you begin to hear the airplane. When the blue lines stop, you no longer hear the airplane. For this and each question below, answer the following: a) From which direction did the sound of the airplane come from (ahead of you, above you, or behind you) when you first heard the plane; b) When did the sound disappear? Was it when the airplane was behind you, above you or in front of you?; c) Answer this question in regards the the REAL LOCATION of the plane that you see on the activity (but really can't see if it's cloudy). When you heard the airplane first, where was it physically located on that cloudy day... was it behind you, right over your head, in front of you, or was way ahead of you and you couldn't see it even on a clear day. Example: a)The sound first appeared from behind me... b) example.. The sound disappeared after it had traveled out of site...c) example: It was physically behind me when I first heard the sound.
  • Set the plane to sound speed ratio to 1 (They are both going the same speed). Click on Reset and then on Start.
  • Set the plane to sound speed to 2 (the plane is going twice the speed of sound). Repeat as above
  • Set the plane to sound speed of 3 and then 4, repeating as above (answering the three questions (a,b and c as desciribed above) each time.

Answer the following question: If you are walking in a city and a terrorist airplane comes toward you at low altitude at 4 times the speed of sound, when will you first hear the sound of the approaching aircraft. TELL WHY. HAND IN EACH ACTIVITY 1) MOVING POINT SOURCE AND 2) SUPERSONIC JET AIRCRAFT TO THE DIGITAL DROP BOX. Don't forget the graph in Activity 1.

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Calculate quantities involving wavelength, wave speed, and frequency

Solving problems-1

Solving problems-2

 

 

Supplementary: RESONANCE AND STANDING WAVES

Natural frequency

Forced vibration

Standing wave patterns

Fundamental frequency and harmonics

 

Supplementary: MUSICAL INSTRUMENTS

Resonance

Guitar strings

Open end air columns

Closed end air columns

 

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