Download Wave Characteristics

Wave Characteristics
Terms to Review
Parts of a Wave
– Crest
– Trough
– Pulse
– Amplitude
– Wavelength
– Frequency
– Period
Types of Waves
– Mechanical Waves
– Electromagnetic
Waves
– Transverse Waves
– Longitudinal Waves
– Surface Waves
Calculations to Know
Speed of wave (velocity)
= freq x wavelength
Frequency = cycles/second
Period = seconds/cycle
Frequency = 1/period
Period = 1/frequency
Characteristics of Waves
 Amplitude of a wave is its maximum
displacement from the rest or equilibrium
position.
Slinky Waves
 Hand of one partner = vibrating source of energy
 Slinky = material medium through which energy is
transferred
 Frequency of wave = number of complete cycles
passing a given point in a unit of time (i.e. a second)
 Frequency of wave is determined by the source
(person)
 Once a wave is produced, its frequency will never
change (even if the speed and wavelength change)
 As wave travels through the slinky, its amplitude
usually decreases as some energy is lost to friction
Principle of Superposition
 When two waves are travelling through
medium at same time (sent pulse from
either direction)
 Principle states that: displacement of a
medium caused by two or more waves is the
sum of the displacement caused by the
individual waves
 Result of superposition of two or more
waves is called interference.
Types of Interference
1) Constructive Interference
- two pulses travelling in the same direction
- results in wave with a larger amplitude
that any of the individual waves
Types of Interference
2) Destructive Interference
- two pulses travelling in the opposite
direction
- results in a wave with a smaller amplitude
Wave Behaviour at Different
Media
 Speed of wave depends only on properties of
the medium
– Speed of water waves depends on depth of water
– Speed of rope wave depends on force exerted on
rope
– Speed of sound wave depends on temperature of
air
Speed of wave = frequency x
wavelength
 This means, for a given medium,
– higher frequency = shorter wavelength
– lower frequency = longer wavelength
Speed of Slinky Waves
 Speed of wave doesn’t depend on amplitude
or frequency of the wave...it only depends
on the properties of the medium.
 For example, you can’t make a sound wave
travel any faster by shouting quicker...the
medium (air) is still the same.
Waves in Different Media
 Design an experiment to test the speed of waves in
different media
 Prove that the speed of waves depends only on the
media – a wave in the same media will always have
the same speed
 Hand in:
1)
2)
3)
4)
5)
6)
Question
Prediction
Materials
Procedure
Data/Observations
Conclusion
Wave Behaviour in Different
Media
 Waves typically move from one media to
another (i.e. Light wave from air to water)
 When a wave (incident wave) reaches a
boundary of a medium, some of the wave
energy continues into new medium (transmitted
wave) and some of the wave energy is
reflected back (reflected wave)
 The wave that continues on (transmitted wave)
will have the same frequency as the original
wave (incident wave)
Wave Behaviour in Different
Media
 If the difference in media is small:
– Amplitude of transmitted wave almost = incident
wave
– Amplitude of reflected wave = small
– This means most energy is transmitted to new
medium
 If the difference in media is large:
– Most of wave energy will be reflected
– As a result, amplitude of the reflected wave will
almost = amplitude of the incident wave
Wave Behaviour in Different
Media
 When wave passes from a less dense to a
more dense medium (i.e. Slinky wave hitting
a wall)
– The reflected wave will be inverted
 When a wave passes from a more dense
media to a less dense medium (i.e. Slinky
wave to air)
– The reflected wave will be erect
Waves Speeds in Different Media
 Wave from a light spring moving to a heavy
spring:
– Frequency of waves are the same (remember
frequency only depends on the source
producing the wave)
– Speed of the wave in the heavier spring is
slower
– Using our equation (velocity = frequency x
wavelength), less speed = smaller wavelength
– If speed of wave increases in the new medium,
wavelength will be larger
Standing Waves
 When two pulses with equal, but opposite amplitude
meet, one point in the medium will remain
completely undisturbed
– This point is called a node
– At a node, the medium is never displaced
– It is produced by destructive interference
 When two pulses with equal amplitude in the same
direction meet, one point in the medium undergoes
the greatest displacement
– This point is called an antinode
– At an antinode, the medium has the greatest
displacment
– It is produced by constructive interference
Standing Waves
 Standing waves
are produced by
identical waves
travelling in opposite
directions
 The wave appears
to be standing still
 It has both nodes
and antinodes
Complete Wave Ripple Tank Lab
http://phet.colorado.edu/en/simulati
on/wave-interference
Wave Reflection
Law of Reflection:
The angle of incidence is equal to the angle
of reflection
Wave Refraction
 Refraction = what happens when waves move from
one medium to another (i.e. From shallow to deep
water)
– Shallow waves have shorter wavelength (since
frequency stays the same, velocity must decrease)
 When waves enter different media, the direction of
the wave can change. This is known as refraction.
Wave Diffraction
 When waves pass
through small barrier,
they bend around
edges forming
circular waves
 Spreading of waves
around the edge of a
barrier is called
diffraction
Wave Interference
 When two waves pass
through a barrier, both are
diffracted (become circular
waves) PLUS the two waves
interfere with eachother
 Interference produces
regions of constructive and
destructive interference
– Constructive = two crests or
two troughs meet
– Destructive = a crest meets a
trough
Water Interference
 Constructive
interference creates
antinodes while
destructive interference
creates nodes
 This pattern produces
“antinodal lines”
 Between antinodal lines
are areas when crests
meet troughs – these
are nodal lines