1. Chapter 4 The Perception of Light & Sound
Text Book pp. 91 to 116
Related concepts: Waves, Vision, Hearing, Telescopes
Radio IR UV
X Rays
Gamma

2. Waves
A Wave is a disturbance that travels through a medium or the vacuum of space.
A wave carries energy
A wave does not transport matter.

3. Transverse Waves The movement or vibration is “up and down”
A transverse wave’s motion is perpendicular to its travel (Its Energy vs its medium)
Energy Travel
Vibration

4. Longitudinal or Compression Wave
The vibration is “forward and backward”
The direction of vibration (medium) is the same as the direction of wave travel (energy)
Vibration
Direction of Travel

5. Mechanical Waves
Mechanical waves need a substance or “medium” to travel through.
Examples:
Sound Waves (air, water, metals)
Seismic Waves (earth, rock)
Ocean Waves

6. Electromagnetic Waves
Electromagnetic waves do not need a substance or medium in order to travel.
They may travel through empty space or a medium.
Radiant Energy
Examples:
Radio waves
Infrared waves
Visible light
Ultraviolet light
X rays
Gamma rays

7. EMR Spectrum How EMR is organized
Longest to shortest wavelength of the spectrum
Radio, TV, Micro, IR, Visible, UV, X ray, Gamma
Equates to lowest to highest energy and frequency.

8. Sound
Sound is carried by longitudinal (compressional) mechanical waves
Sound needs a medium to travel through
In the vacuum of space, sound will not travel.
The speed of sound in: Air is 350 m/s or over 1200 km/h
That seems fast, but it is way slower than light, which travels km/s

9. The Decibel Scale
The decibel scale measures the intensity, or loudness of sound as perceived by the human ear. (amplitude= degree of compression)
Sound
Decibels (dB)
Breathing, 3 m away 10
Murmur or whisper, 2 m away 20
Calm classroom 40
Intense road traffic, 3 m away 70
Motorcycle, without muffler, 2m away
100
Rock Concert / Jet engine (14m away)
120
Space Shuttle launch (50 m away)
200

10. Frequency & Wavelength
Sound also has frequency and wavelength
Frequency is measured in Hertz (Hz), also called cycles per second. Its how many vibrations there were per second.
Wavelength is measured in metres or centimetres
The higher the frequency of a sound, the shorter its wavelength is and the greater its energy.

11. Frequency and Pitch of Sound
High frequency sound waves (>1000Hz) have a very high pitch sound (high treble).
Low frequency sound waves (<100 Hz) have a low pitch (bass)
Mid-range sounds (100Hz to 1000Hz) are the most comfortable to the ear.
The range of human hearing is:
20Hz to 20000Hz (on the average)
TEST YOUR HEARING!!!

12. Infrasound and Ultrasound
Frequencies below 20Hz are called infrasound.
Humans can’t hear them, but some animals, like elephants, can.
Frequencies above Hz are called ultrasound.
Humans can’t hear them, but some animals, like dogs and bats, can
Bats use ultrasound to locate objects in the dark (echolocation)
Hospitals use ultrasound to “see” the development of a fetus.

13. Different light frequencies are interpreted as colours
Visible Light
Light is a form of electromagnetic radiation (EMR) that humans can see with their eyes.
The different frequencies of light are interpreted by our brains as different colours
Different light frequencies are interpreted as colours

14. Refraction
Refraction is the deviation (bending) of light as it passes from one transparent medium to another.(Incident ray Refracted ray) speed decreases
For example, light refracts when it passes from air into glass or water.
The spoon looks bent
Due to refraction
Air
Water

15. Lenses Lenses use refraction to collect, focus or project light.
Lenses are made of transparent material (like glass) and have at least one curved surface.
The two main types of lens are converging and diverging that have the ability to refract light.
All of these devices use lenses:
Contact lens, eye eyeglasses telescope projector camera photographic lens

16. Converging, or convex, lenses focus light at a single focal point.
Optical Centre
Converging, or convex, lenses focus light at a single focal point.
Converging lenses can be used to create “real” images… Images that can be projected on a screen.
Converging lenses are often used to enlarge or magnify images.
Focal point
Diverging, or concave, lenses do not focus light at a single point.
The so-called focal point of a diverging lens is a virtual point where the image would appear to be when viewed through the lens.
Diverging lenses cannot project images onto a screen. Diverging lenses always make smaller images.
Focal point
Optical Centre

17. How to Find the Image (Image when object is between 2F’ and F’)
2. Tip of object, parallel to base line
Lens Plane
Base line
3. Tip of object through F’. F’
2a. From lens plane, through Focal point (F)
Object
1. Tip of object through OC
Image
Converging
(biconvex)
Lens
In this case, when the object is between F’ and 2F’, the image is larger than the object, upside down, and real. (3 on pg. 114)

18. How to Find the Image (Image when object placed past 2F’: 1 on pg. 114)
2. Tip of object, parallel to base line
1.Tip of object through OC
Lens Plane
2a. through Focal point (F)
3. Tip of object through F’
Base line F’
Upside down
Smaller
Real
Image
Object
3a. Parallel to base line
Converging
(convex)
Lens

19. How to Find the Image (Image when object placed closer than F’)
2b. From focal point through lens
2. From lens, parallel to first line
Lens Plane
Base line . F’
Image
Right side up
Larger
Virtual
Object
1. Tip of object through O.C.
Converging
(biconvex lens)
5 on pg. 114

20. Object
Image
Small,
Virtual
Right side up
Diverging Lens (biconcave) seen through a diverging lens, the image is smaller than the object, but right-side up.

21. Glasses
Myopia: Near-sighted people need diverging (concave) lenses in their glasses. Eyeball is too deep
Near sighted people can see better close up, but not far away
Hyperopia: far-sighted need converging (convex) lenses in their glasses. Eyeball is not deep enough.
Far-sighted people see things far away better, but cannot see close things as well.

22. Exercises
Workbook, pages