Waves and Lenses
Pg. 92-116
What is a WAVE
• Wave: disturbance that travels through a
medium (water, air, ground…)
• Transports energy
• It does NOT transport matter
• Ripples are the result of a disturbance that
spreads across the surface of the water
• Picture a duck sitting in waves, the duck rises
and falls but never moves Fig 4.2
Wave Characteristics
• Propagates (spreads) in two ways: transverse
and longitudinal
• Transverse: its medium moves perpendicular
to its motion
• Fig 4.3
• Wave moves from left to right, but medium
moves up and down
Wave Vocab
• Highest point of wave: Crest
• Lowest point of wave: Trough
• Transverse waves are made up of Crests and
Troughs
Longitudinal Wave
• Medium moves parallel to the motion of the
medium
• When a longitudinal wave propagates through a
medium, its particles move closer together and
then farther apart
• BUT always parallel to the direction of the wave’s
motion
• Compression: region where particles are close
together
• Rarefaction: region where particles are farther
apart Fig 4.5 and 4.6
Amplitude
• Amplitude (A) of a wave: Depends on the energy
transmitted by a wave
• The greater the energy transmitted, the greater
the amplitude
• (when you make a rope make waves, the higher
the waves the more energy you must put in)
• A: maximum distance travelled by a particle in
the medium compared to its position at
equilibrium
• Frequency of a wave connects with the Pitch of a
sound
Amplitude cont.
• Transverse waves Amplitude: max. height of
crest or max. depth of trough, from the
position at equilibrium Fig 4.8
• Longitudinal waves Amplitude: harder to
measure. Depends on density of compression
– The denser the region of Compression , the
greater the Amplitude
– Fig 4.9
• Amplitude= Loudness of the sound
Wavelength
• ‘Lambda’ (λ)
• Is the length of a wave’s complete cycle
• Transverse wavelength: distance between 2
consecutive crests or troughs
• Longitudinal wavelength: length of 1
compression and 1 rarefaction
• Fig 4.10 and 4.11 (copy in notes)
Frequency
• Frequency: number of cycles per unit of time
• Measured in Hertz (Hz)
• If a wave has a frequency of 1Hz, it completes
one full cycle in one second
• Speed= frequency x wavelength
Types of Waves
• 2 types of waves:
– Mechanical
– Electromagnetic
• Mechanical wave: a wave that requires a
medium (solid, liquid or gas) in order to
propagate (spread out)
• Ex: water is the medium for water waves, air is
medium for sound waves, ground is medium
for seismic waves during earthquake
Types of Waves cont.
Did you know that there is no
• Electromagnetic wave: is a wave that can
sound
in
space….but
our
movies
travel in both vacuum and a medium
be boring
without
this,
•would
Ex: light waves
(transverse
waves) that
moveso
just as easily
in a vacuum
as a medium
– Sun
movie
makers
ignore
this fact
to
rays reach us through interstellar space and
make
it more interesting for the
the atmosphere
•viewer!!
Electromagnetic waves carry energy from
point to another
– Form of energy is radiant waves
Types of waves cont.
• Electromagnetic waves ex: radio waves, light
waves, ultraviolet waves, X-rays…
Pg. 98-99
•
•
•
•
•
Create a table in your notes using these pages
Title
Description
1 example you choose
1 example related to health care
Sound Waves
•
•
•
•
Sound: longitudinal mechanical wave
Produced by vibration of an object
Transmitted to the object’s environment
Ex: chair falls to floor, its impact causes
particles in floor to vibrate, these disturbances
are passed on to the surrounding medium (ex:
air) the wave produced transmits sound
energy
The Decibel Scale
• Sound can be soft like a whisper or loud like a
scream
• Volume depends on intensity or energy is it
transmitting
• The greater the energy the greater the sound
• Less energy = less amplitude = less sound
• Intensity of sound is measured in Decibels
(dB)
Decibel (dB)
• Not an exact scale, relative to perception by
the human ear
• Decibels are measured in 10s, so when
something is increased by 10 dB, it becomes
10 times louder
• Sound measuring 40dB is 100 times louder
than a 20dB sound
• Decibels are not cumulative (two separate
50dB do not make 100 dB)
Dangerous Decibel levels
• Fig 4.20
• Prolonged exposure to sounds louder than
100 dB can cause long-term hearing damage
• Starting at 120 dB pain and immediate hearing
loss can ensue (ear protection needed)
Light Waves pg. 106
• Light is an electromagnetic wave that is visible
to the human eye
• Ex: light bulb, sun, fire
• Light waves travel in straight lines AKA light
rays
• Light waves can be reflected or refracted
when they strike an object
Reflection
• Reflection: rebounding of light that occurs
when a light ray hits a different medium and
‘bounces back’ to the original medium
• Ex light rays passing through air and
rebounding off of a mirror
• If we can see an object it is because reflection
brings light to our eyes
• Fig 4.26 copy this diagram into your books and
label the lines
Reflection cont.
• Incident ray: ray that contacts the surface of
an object
• Reflected ray: ray that rebounds
• Normal: is a line perpendicular to the surface
at the point of reflection
• Angle of incidence: angle formed by the
incident ray and the normal
• Angle of reflection: angle formed by the
reflected ray and the normal
Reflection cont.
• Reflection:
– Diffuse reflection
– Specular reflection
• Diffuse reflection: most objects have rough
surfaces (paper or balloon), when parallel
lines hit the uneven surface they reflect in all
directions (light rays do not respect the laws
of reflection)
Reflection cont.
• Specular reflection: light contacts a perfectly
smooth surface (ex: mirror), rays follow laws
of reflection
• When parallel light rays contact a smooth
surface their reflection is parallel
• Producing a true mirror image
Reflected image
• Image appears to be behind the mirror at the
same distance as the reflected object
• AKA Virtual Image (made by the prolongation
of reflected rays) not the real rays!!
• Real Image is made by real crossing of light
rays
• Image is the same size as object
• Image is horizontally inverted (the left is now
the right side)
Reflected Image pg. 109
• Can localize Virtual image beyond plane of
mirror by drawing incident rays from the
object and the resulting rays
• Image produced at the meeting point of the
prolongation of the reflected rays
• Fig 4.31
Plane mirrors
• Change the trajectory of light rays by
reflection
• Increase the observer’s field of vision
– Think of a review mirror on a car, or the mirror
your dentist uses
• They change the trajectory of light rays so the
rays can reach the eye of the observer
Refraction
• Refraction: the deviation of light ray as it
passes from one transparent medium to
another (ex: air to water)
• Fig. 4.33 take a look!
• Lenses help to refract light as it passes
through them
Lenses
• Lenses:
– objects made up of transparent materials
– have at least one curved surface
– ability to refract light as it passes through them
• 2 types of lenses:
– Converging
– Diverging
Focal points
• There are 2 focal points between diverging
and converging lenses
– Principal Focal Point (F)
– Secondary Principal Focal Point (F1)
• Pg 112 look at the images
Converging Lens
Converging lens
• Focal point of converging lens real point
where the refracted rays actually meet when
the incident rays run parallel
• Ex: magnifying glass
Diverging Lens
Diverging lens
• Focal point of diverging lens is the virtual
point from which the refracted light rays
appear to emanate when the incident rays run
parallel
Applying what you know…
• Pg. 114 image has many outcomes, lets look at
them all...
• Pg. 115 image is virtual and smaller than
object