Wave Behaviour

Wave Behaviour
Inquiry question: How do waves behave?
Students:
● explain the behaviour of waves in a variety of situations by investigating the phenomena of:
– reflection
– refraction
– diffraction
– wave superposition (ACSPH071, ACSPH072)
● conduct an investigation to distinguish between progressive and standing waves
(ACSPH072)
● conduct an investigation to explore resonance in mechanical systems and the relationships
between:
– driving frequency
– natural frequency of the oscillating system
– amplitude of motion
– transfer/transformation of energy within the system (ACSPH073)

Open Ended

What is the frequency of this wave?

Wave Interactions

• Mechanical waves transfer energy

through a medium.

• When that medium physically ends or

changes the wave does not stop.

• The energy the wave is carrying

undergoes three processes:

• Some energy is reflected
• Some energy is absorbed
• Some energy is transmitted

Reflection

• When a transverse wave is reflected the amplitude of the reflected wave is not

quite the same as the original.

• Some of the energy of the wave is absorbed by the boundary and some will

travel through it.

• The more rigid and/or dense the boundary is the more the wave energy will

be reflected and the less it will be absorbed.

• However some energy will always be absorbed.

Multiple Select

A wave travels along a rope and reaches a fixed end. What occurs next?

• the wave is reflected

• the reflected pulse is inverted

• No change to the amplitude

• No change of phase

Reflected Wave Fronts

• 2D and 3D waves (e.g. water waves) travel

as wave fronts.

• When wave fronts are drawn, what is

drawn are the crests of the waves.

• When close to the source wave fronts can

have significant curvature, but a long
distance from the source are nearly
straight (this is called a plane wave).

• The direction of the wavefront is shown

by a line (called a ray) that is
perpendicular to the wave front and in
the direction that it is moving.

Multiple Choice

Which of the following properties of a wave can change when the wave is reflected:

• frequency

• amplitude

• wavelength

• speed

Reflected Wave Fronts

• When using rays to show a wave front

hitting a surface, we us an imaginary
line called the normal, that is
perpendicular to the surface.

• The angle from the normal that a wave

strikes the surface at (angle of
incidence) is the same as the angle
from the normal to the reflected wave
(angle of reflection).

• This is the law of reflection, stated as i = r

Labelling

Label the diagram

Drag labels to their correct position on the image

angle of incidence

angle of reflection

reflected ray

incident ray

Normal

Draw

Draw the reflected rays for the incident rays.

Multiple Choice

Is the last example of specular reflection or diffuse reflection?

• specular

• diffuse

Refraction

• Refraction is a change in the direction of a wave, caused

by a change of it’s speed.

• This occurs when a wave passes from one medium into

another.

• The direction of the refraction depends on whether the

wave speeds up or slows down as it enters the new
medium.

• Waves refract away from the normal when they speed

up .

• Waves refract towards the normal when they slow

down .

• (Remember that when a wave changes speed its

wavelength also changes, but not its frequency).

Multiple Choice

When light travels from the air into the water, which of following changes?

• speed

• amplitude

• frequency

• period

Diffraction

• When a plane wave passes through an

opening, or around an obstacle, it bends.

• This bending is known as diffraction.

• Diffraction is significant when the size of the

opening or obstacle is similar or smaller than
the wavelength of the wave.

• If the wavelength is much smaller the

diffraction is less.

​Bending of light around the corners of door and windows.

​Sun rays coming from the clouds.

​Light peeping out through two blades, when they are places in the manner shown below .

Multiple Choice

which of the following is not the example of diffraction?

• Colors on a CD/DVD

• Electron microscope

• Sound bending around corners

• formation of shadow

Superposition

• Principle of Superposition: Superposition

occurs when multiple wave interact their
amplitudes are added together.

Superposition

• This can be constructive (waves become

bigger) or destructive (waves become
smaller).

• When any two waves meet and combine

there are places where constructive
superposition occurs and places where
destructive superposition occurs.

• This concept is used in noise cancelling

headphones.

Multiple Choice

What will the superposition of these two pulses look like in 3s?

Open Ended

A ray strikes a flat surface at an angle of 38° measured from the surface. What is the angle of reflection of the ray?

Multiple Choice

The following diagram shows a wave before and after being reflected from an object. What is the shape of the object?

• flat

• concave

• convex

• parabolic

Multiple Choice

What phenomenon does the diagram below demonstrates?

• diffraction

• interference

• reflection

• refraction

Standing Waves

• A standing wave occurs when a new

wave interferes with the reflection of
the first wave in a way that the 2
superimposed waves create a single
larger amplitude wave.

• It is called this as it does not appear to

be travelling up and down, but
oscillating up and down in a fixed
pattern.

• i.e. the medium is just flipping up and

down in the same place.

Labelling

label the diagram

Drag labels to their correct position on the image

antinodes

nodes

Resonance: The Vibrant Harmony of the Universe

Resonance is the phenomenon where a system is driven to oscillate with greater amplitude at certain frequencies than at others. This fundamental property of waves and systems plays a crucial role in various scientific fields, from physics to engineering.

Natural Frequency: All objects that can vibrate tend to do so at a specific frequency.

​Resonance

Driving Frequency

External frequency applied to the system.

When driving frequency equals to natural frequency, amplitude of a system's oscillation increases.

• driving frequency = natural frequency

• energy of force is transferred efficiently to system

• increase in amplitude

​Resonance

Multiple Choice

Resonance occurs when the driving frequency of a vibration exactly equals the natural frequency of vibration of an object.

• the amplitude of vibration will decrease

• the amplitude of vibration will increase

• the frequency of vibration will decrease

• the frequency of vibration will increase

Multiple Choice

in the graph, two of the wave forms superimpose to create the third wave form. which wave is the result of the superposition of the other two?

• red

• green

• blue