Read page 91 aloudPing pong ball demo!! Ping pong ball in the tank and make waves
Page 98 in their book
Because it is mechanical sound cannot pass through a vacuum!!!!
Mach 1 is the speed of sound!!!!Supersonic planes can reach Mach 2.
The decibel scale is a relative scale that represents the perception of the intensity of sound by the human ear.
Lower frequency sounds are lower on a piano keyboard.Higher frequency sounds are higher on the keyboard.
Not heard by humansElephants emit infrasounds to communicateDolphins communicate with ultrasounds.Dogs can be trained with ultrsound whistles
What are some sources of light?Light comes from many different sources; the sun, a fire, light bulbs…We will be studying reflection and refractionHow do you experience light absorption
Bounce a ball to show reflectionWe see objects because they are reflecting the light and it reaches our eyes.
Time to do some worksheets – we will start the lab next day!!!
The light bends because the light ray travels at a different speed as it passes through a new medium
What are lenses used for:EyeglassesMagnifying glassesCamerasMicroscopes and telescopes
of Light and
1 – What is a wave?
A wave is a disturbance that travels through a medium.
A wave transports energy.
A wave does not transport matter.
What is a disturbance?
A localized and temporary change in the properties of a
1.1 – Wave Characteristics
There are 3 characteristics of waves:
How the waves propagate (travel)
The amplitude of the wave
The frequency of the wave
How waves propagate:
Transverse and Longitudinal
A transverse wave is a wave that propagates perpendicular to
the motion its medium.
There are crests and troughs
A longitudinal wave is a wave that propagates parallel to the
motion of its medium
The particles move closer together and then farther apart BUT
always parallel to the wave’s motion.
Close together = area of compression
Farther apart = area of rarefaction
The amplitude (A) of a wave corresponds to the maximum
distance travelled by a particle in the medium compared to its
position at equilibrium.
Amplitude of a transverse wave:
Amplitude of a longitudinal wave:
Smaller amplitude because it
is not as compressed as in the
The amplitude depends on the energy transmitted by a wave.
More energy = greater amplitude
Less energy = lower amplitude
Shall we give it a try?
Wavelength is the length of a wave’s complete cycle.
Symbolized by the Greek letter lamda, λ
The frequency is the number of cycles per unit time.
How fast the waves go by!
Frequency is measured in Hertz, Hz.
A Hertz is the number of cycles per second.
1 Hz = 1 full cycle per second
1.2 – Types of Waves
There are two types of waves:
A mechanical wave is a wave that requires a medium in order
The medium may be a solid, a liquid or a gas.
Mechanical waves cannot travel in a vacuum.
Waves travel in water
Sound waves travel in air (gas)
Seismic waves travel in the earth (solid)
Mechanical waves are caused by localized disturbances.
The disturbance changes the physical properties of the
medium; such as amplitude and frequency.
The changes are transmitted to the neighboring particles.
An electromagnetic wave is a wave that can travel through
both vacuum and a medium.
Light from the Sun is electromagnetic.
Travels through space and the atmosphere
The speed of electromagnetic waves depends on the medium it
is travelling in.
The speed of light in a vacuum is
300 000 km/s OR 300 000 000 m/s
Types of Waves
Can only move in a
Can travel in a
medium or a vacuum.
Seismic waves, sound
waves, water waves
Radio waves, light
The Electromagnetic Spectrum
This organizes all electromagnetic waves according to their
wavelength and frequency
The smallest frequency and the longest wavelength
They are invisible and transport little energy.
Microwaves are radio waves with a higher frequency which
makes certain particles vibrate and raises their temperature.
Magnetic resonance imaging (MRI)
Microwave ovens, cell phones, radar
They are invisible but we feel the warmth they
Infrared thermography, night vision goggles,
space observation satellites, short distance
communication (remote controls, optical
scanners, optical computer mouse, wireless
Can be seen by humans
Each color has its own wavelength
All of these colors together make up white light
Lighting, laser technology, photography, cinema, computer screens,
UV rays are invisible to humans but can be seen by some
The greater frequency means more energy is transported by UV
Cause suntans and can cause cancer
Our body needs UV rays to produce vitamin D
Treatment of rickets and jaundice, sterilization of medical
Transmit a large quantity of energy!!!
Allow us to see through many opaque objects
Used to examine bones!!
Prolonged exposure can cause cancer and burns.
Radiography, baggage inspection, study of crystalline
Travel very easily through matter.
1 cm lead, 6 cm concrete or 9 cm of earth only block 50% of UV
Can cause burns, cancer and genetic mutations.
2 – Sound Waves
Sound is a longitudinal mechanical wave produced by the
vibration of an object and transmitted to the objects
Anything that creates sound produces a longitudinal
Our larynx has folds on tissues that act like guitar strings.
They vibrate with the passage of air, creating sounds.
We only here sounds when the sound waves contact the
The eardrum vibrates in rhythm with the sound waves.
The eardrum vibrates near the fluid filled cochlea.
The cochlea has many receptor cells that capture the impulses.
The auditory nerve transmits this information to the brain
where it is analyzed.
Sound travels through solids and liquids, as well.
The vibrations can be felt!!!
2.1 – The Speed of Sound
The speed of sound varies depending on the medium it is
2.2 – The Decibel Scale
The volume of a sound depends on the energy it is transmitting.
Greater energy = louder
Greater amplitude = louder
The decibel scale is by factors of 10.
When a sound increases by 10 dB, it is 10 times louder.
A sound measuring 20dB is 100 times louder than a 0 dB sound
(10 x 10)
A 40 dB sound is 100 times louder than a 20 dB sound
Prolonged exposure to 100 dB sounds can lead to permanent
Sounds 120dB and above can cause pain and immediate
Human breathing ( at a distance of
3 m away)
Murmuring ( at a distance of 2 m
Busy department store
Intense road traffic (3 m away)
Motorcycle – no muffler (2 m
Rock music concert
Jet engine (14 m away)
Spacecraft engine (50 m away)
2.3 – Frequency and the Perception of
Sound can also have different tones – higher and lower pitch
The tone of a sound depends on the frequency
The average humans can hear sounds with frequencies ranging
from 20 to 20 000 Hz.
Read page 104. Thoughts?
Infra-sounds and Ultra-sounds
Sounds under 20 Hz infra-sounds
Sounds higher than 20 000 Hz are ultrasounds
Bats use echolocation
Ultrasonic waves are emitted and their echoes are used to find
Sonars used in boats use the same principles
3 – Light Waves
Light is an electromagnetic wave that is visible to the human
Light travels in a straight line – hence, light rays!!
Light rays are reflected, refracted or absorbed when they strike
3.1 - Reflection
This occurs when a light ray travels through one medium and
rebounds when it strikes another medium.
Air mirror (simple example) air
All objects reflect light to varying degrees.
Something to think about:
Black objects absorb all colors of light
White objects reflect all colors of light.
The actual color we see is the colors that are reflected!!
Colors are not usually pure.
An object has the main color and a bit of the colors on each
side of the main color!!!
Some terms to know:
Incident ray – the ray that contacts the
surface of an object
Reflected ray – the ray that rebounds
from the object.
The Normal – a line perpendicular to the
surface at the point of reflection.
Angle of Incidence – the angle formed by
the incidence ray and the normal.
Angle of Reflection – the angle formed
by the reflected ray and the normal
Lab 33 – Image in a Plane mirror
Some terms to know:
A virtual image is an image that cannot be formed on a screen
A real image can be formed on a screen.
Inverted - An image in which up and down, as well as left and right, are
When an object is laterally inverted, the left and right are interchanged.
If the object is “upside-down” it is dorsally inverted
Lab 33 – Answers and thoughts!!!
What we learned from our lab on plane
angle of incidence is always equal to the angle of
incidence ray and the reflected ray are always on
the same plane.
There are two types of reflection:
Diffuse reflection which occurs when objects have a rough surface
Parallel light rays hit a rough surface and the rays are reflected in all
Specular reflection occurs when light rays hit a smooth surface.
When parallel light rays contact the smooth surface, the
reflected rays are parallel.
Produces a mirror image
Things to remember about images in plane mirrors:
The image appears to be behind the mirror, at a distance equal
to the distance between the mirror and the object
The image is virtual, the image cannot be captured on a screen.
The image is the same size as the object.
The image is horizontally inverted (left is right and right is left)
Application of plane mirrors:
The uses of plane mirrors are based on these two principles:
They change the trajectory of light rays by reflection
They increase the observer’s field of vision
Rear view mirrors, mirrors used by dentists, mirrors in cameras,
3.2 - Refraction
The deviation of a light ray as it passes from one transparent
medium to another.
When light bends as it passes from one medium to another
3.3 - Lenses
Lenses use the principle of refraction.
Lenses are made of transparent material and have at least one
There are two types of lenses
Converging lenses bring the light rays together as the light
passes through the lens.
Diverging lenses spread the light rays aart as the light passes
through the lens
The optical center (OC) is the center of the lens.
The principal axis is the straight line that runs perpendicular to
the surface of the lens and through the OC.
Focal Point of a Lens
The focal length of a converging lens is the real point where the
refracted rays actually meet when the incident rays run parallel.
The virtual point from which the refracted light rays appear to
emanate when the incident rays run parallel
Images obtained with a diverging lens are always the same, no
matter where the object was placed in relation to the lens.
The image is always:
not inverted (right side up)
smaller than the object
The cornea of an eye is a converging lens
Muscles adjust the shape to allow objects to be focused on the retina
The image formed on the retina is smaller and inverted.
The brain analyzes the image
- Nearsightedness – cannot clearly see objects that are at a
- Caused by the image forming in front of the retina
- Corrected with a diverging lens
- Farsightedness – cannot clearly see objects that are up
- Caused by the image forming behind the retina
- Corrected with a converging lens
Presbyopia is caused by the aging of the lens ‘ muscles
The lens can no longer adjust its shape to clearly see objects
close up – no longer as elastic
The image is formed behind the retina.
Corrected by a converging lens.
surgery helps reshape the cornea
surgery can correct myopia and hyperopia
cannot correct presbyopia