1. Chapter 7 General Science
Waves, Sound & Light
Chapter 7
General Science

2. Waves
Waves are vibrations in matter, produced by energy moving thru a medium.
There are 2 types of waves
Mechanical
Use matter to transfer energy through a medium
Produce sound, waves in water
Electromagnetic
Do not need matter to transfer energy
Produce light, x-rays, heat (infrared), etc.

3. Mechanical Waves
Waves that REQUIRE a medium through which energy travels (the medium is a substance that carries the energy, like water or air. Examples: waves in water, sound waves, energy moving through a slinky. Others?
Energy causing a wave is transferred from particle to particle as it moves thru the medium.

5. Two Basic Types of Mechanical Waves
Transverse Waves
Energy travels thru wave causing particles to move at a right angle to the direction of energy.
Usually drawn as up & down bumps
Ripples on a pond are an example of these.

6. Another type of Mechanical Wave
Compression or Longitudinal Waves
In this type, particles move in the same direction as the energy.
Sound is a compression wave.

7. Transverse Wave Examples & Demo

8. Wave Properties Parts of a Wave Amplitude Wavelength Frequency
Human perception of amplitude is loudness
Human perception of frequency – pitch
Online Tone Generator.  

9. Transverse Wave Properties
Parts of a Wave
Crest – very top
Trough – very bottom of wave
Amplitude – Distance between resting position & either the crest or trough
Wavelength – Distance from top of 1 crest to the next

10. Transverse Wave Properties (cont.)
Frequency: # of wavelengths to pass by a given point in 1 second
Frequency & Wavelength are related
As frequency increases wavelength decreases
As frequency decreases wavelength increases

11. Transverse Wave Properties (cont.)
Pitch: degree of highness or lowness of a sound.
Frequency & Pitch are related.
As frequency increases pitch gets higher
As frequency decreases pitch gets lower
Online sound generator

12. Compressional or Longitudinal Waves
Medium travels slightly back and forth thru the medium, in the same direction as the energy moves;
Almost the same properties as a transverse wave

14. Sound Sound is produced when an object vibrates.
When an object vibrates it exerts a force on surrounding air which travels to an organism’s eardrum
Loudness of a sound is recorded in decibels
As a sound gets louder, amplitude of the wave increases

15. Sound The moving air mass carries vibrations to your ear
The air is the MEDIA that it travels through.
Medium is what the wave travels through (ex. solid, liquid, gas)
NO MEDIUM means NO SOUND!!!!

16. Wave Interference
Interference occurs when two or more waves strike the same place at the same time and combine to produce a single wave.
Waves can combine in two ways:
Constructive interference: waves combine so that the resulting wave is larger than the two originals.
Destructive interference: If the waves combine so that the resulting wave is smaller than the two originals

17. The Echo
An echo is when a sound wave hits a hard surface and bounces back, causing you to hear the sound a second time
Sonar (SOund Navigation Ranging) uses echoes. It is a measure of how long it takes the echo to return to the source of the sound. Can tell you how far an object is from you.
Bats & echolocation:
Biomimicry: Velcro, Radar & Airport Screenings

18. Doppler Effect of a Moving Sound Source: moving towards a person causes the sound to increase in frequency (increase in pitch).

19. Speed of Sound Sound travels at different speeds thru different medium
The more dense a material, the faster sound travels
3355 mph thru water (less in distilled water
7252 mph thru gold
Mach 1 = the speed of sound in air (767 mph in warm air)
Flying at Mach 1

20. Speed of Sound Sound travels better through high-density materials
The closer the molecules are together, the faster they can collide and transfer energy

21. Electromagnetic Waves
These waves do not need matter to travel so can travel thru a vaccum. Are transverse waves.
Difference between the different parts of the EM spectrum is their wavelength & energy. Examples: Light, radio waves, x-rays, gamma rays & more.

22. Visible Light in the EM Spectrum
Light is a small portion of EM spectrum.
It is the only part we can see.

23. What is Light?
Light is energy that is produced by accelerating electric charges
Energy carried in packets called photons.
Light has both a particle nature AND a wave nature. Animations. Demo.

24. Light REFLECTS off of objects.
How do you see?
Light REFLECTS off of objects.
Reflected light enters your eyes & is read by the retina, which sends signals
to the brain.

25. Light and Colors
We see colors because objects reflect certain wavelengths of light
If you see a color, that specific EM radiation wavelength (color) is being reflected while the rest are being absorbed (taken in) by the medium
White reflects all colors
Black absorbs all colors
Plants look green cause
they absorb green wavelengths

26. Opaque, Translucent, Transparent
Objects that do not let light pass through them are opaque. Ex. Walls, your desk, the science book
Objects that let light pass clearly through them are transparent. Ex. Windows, plastic wrap, eye glass lenses
Objects that let only some light pass are translucent. Ex. waxed paper, frosted glass

27. Polarization
A rope analogy illustrates the effect of crossed sheets of polarizing material.

28. Reflection
Reflection is the bouncing back of a wave after it strikes a boundary that does not absorb all the wave’s energy.
The incoming wave is called the incident wave.
The wave that bounces back is called the reflected wave.
The law of reflection states that the angle of incidence is always equal to the angle of reflection.

29. Reflection Sketch

30. Interaction of Waves
The four basic wave interactions that occur when light passes thru materials are:
Reflection
Refraction
Diffraction
Interference
Use this site again to look at the interactions.

31. Refraction
The bending of waves due to a change in speed is called refraction.
Refraction occurs because waves move at different speeds in different mediums.
As waves move from one medium to another they speed up or slow down due to different densities.

32. Diffraction
Diffraction is the bending of waves around the edge of an obstacle.
Diffraction results from a new series of waves being formed when the original wave strikes an obstacle.
The amount of diffraction depends on the wavelength and size of obstacle.

33. Lenses & Mirrors Mirrors reflect light.
Focal point (or focus, F) is where the image appears to be.
Concave mirrors make objects appear larger.
Convex mirrors make objects appear smaller.

35. Lenses Lenses refract light rays.
Their width determines where the focal pt will be.
Concave (diverging) lenses: thinner in middle, sharpen image, for nearsighted people. In cameras, telescopes & binoculars.
Convex (converging) lenses: thicker in the middle. For farsighted people. In magnifying lenses. Microscopes & reflecting telescopes use a convex lens & plane mirror.