Unit 2.4 - The Nature of Waves Flashcards
Progressive waves
A pattern of disturbances travelling through a medium and carrying energy with it
What does a progressive wave involve?
The particles of the medium oscillating about their equilibrium position
Oscillating
Vibrating
Equilibrium position of a particle
Mid point of oscillations
Definition of a wave
Transfer energy without any transfer of matter
When is energy transferred with a wave?
As the wave propagates
What happens as a wave propagates?
Energy is transferred from 1 point in the medium to another
What are the types of progressive waves?
Transverse or longitudinal
What types of waves are transverse and longitudinal waves?
Progressive
Transverse waves
Oscillations (of the particles) are at right angles to the direction of travel of the wave
Example of transverse waves
Electromagnetic waves
Draw a diagram to present a transverse wave
(See notes)
Draw a diagram to represent a longitudinal wave
(See notes)
In which direction are the oscillations in transverse waves?
Perpendicular to the direction of propagation of the wave
Longitudinal waves
Oscillations (of the particles) are parallel to the direction of travel of the wave
In which direction are the oscillations in a longitudinal wave?
In the same direction as the propagation of the wave
Example of longitudinal waves
Sound waves
Draw a graph and label the wavelength, amplitude and 1 complete wave cycle of the wave on it
(See notes)
Displacement (m) (in terms of waves)
The instance of a particle form its equilibrium position at any instant
Amplitude
The maximum value of displacement
Amplitude symbol
A
Which feature of a wave is the same at all point?
Amplitude
Wavelength
The minimum distance between 2 points of a wave which are oscillating in phase
Wavelength symbol
(Lambda)
Frequency symbol
f
Frequency
The number of cycles of a wave that pass a given point in 1 second, which is the same as the number of oscillations performed per second by any particle in the medium through which it is travelling
Unit of frequency
Hertz (Hz)
What is 1Hz equivalent to?
1 wave per second/1 cycle per second
Period symbol
T
Period
The time taken for one complete cycle
Period equation
T = 1/f
What’s f in T = 1/f?
Frequency
What’s T in T = 1/f?
Period
Speed of a wave
The distance that the wave profile moves per unit time
Waves in phase
2 waves that have the same frequency and are at the same point in their cycles at the same time
When are wave sources in phase?
If as they leave the sources, the waves have the same frequency and are at the same point in their cycles at the same time
Antiphase
2 points are said to be in antiphase if they are at opposite points in their cycle at the same time
If a wave is neither in phase or antiphase, what is it in?
“Out-of-phase”
Draw a diagram to explain what a radian is
(See notes)
Radian
An arc equivalent to the length of the radius
The natural unit for angle measurement
What can we talk about between ANY 2 points on a wave?
Phase difference
What is a complete cycle of a wave equivalent to in terms of radians and in degrees?
2πrad
360 degrees
How much are 2 points oscillating in phase in a wave separated by (radians and degrees)?
2πrad
360 degrees
How much are two points oscillating in antiphase out of phase in radians and degrees?
πrad
180 degrees
How out of phase in radians and degrees are two points in a wave that are a quarter of a wave apart?
π/2
90 degrees
How do we calculate the speed of a wave?
c = f(lambda)
Where does the c = f(lambda) come from?
Speed = distance/time
Specific case where the distance moved by the wave is exactly equal to 1 wavelength
Therefore, the time elapsed must equal the period
Speed = distance/time ——> speed = (lambda)/period
Inputting into T = 1/f, using c as the symbol for speed…
c = f(lambda)
What can the equation c = f(lambda) be used for?
Any type of wave
How would we set up plane waves in water?
Ripple tank
Wavefronts
A surface over which the phase of the wave is constant
Draw a diagram of plane waves as a series of wavefronts
(See notes)
3 features of wavefronts
Have all points oscillating in phase
The distance between successive wavefronts is equal to the wavelength of the waves
Are at right angles to the direction of travel (propagation) of the waves
Draw and label a graph of displacement against position
(See notes)
What are the two types of wave graphs we can get?
Displacement against position
Displacement against time
What type of wave can be represented using a displacement position or displacement time graph?
Transverse
What actually IS the displacement against position graph of a wave?
A snapshot (a picture of a wave at a particular time) of a transverse wave
What can we easily determine from a displacement position graph?
Wavelength
Draw and label a displacement against time graph for a wave
(See notes)
What does a displacement against time graph for a wave show?
Displacement of any one particle (or point on the wave) against time
What can we easily determine from a displacement against time graph?
Amplitude and period
What can be calculated from a displacement time graph and how?
Frequency = 1/period
Speed = wavelength/period or frequency x wavelength
On what type of graph can frequency and speed of a wave be easily calculated?
Displacement against time
Polarised wave
A transverse wave in which particle oscillations occur in only one of the directions or planes at right angles to the direction of wave propagation
Draw a diagram to represent a polarised wave
(See notes)
Draw a diagram to represent an unpolarised wave
(See notes)
What type of waves is it not possible to polarise?
Longitudinal
Give examples of things than emit unpolarised light
The sun
Domestic light bulbs
Unpolarised light
Oscillations take place in many directions or planes at once
What does a Polaroid sheet/polarising filter do?
Only allows oscillations in 1 direction to pass through
What can we use to only allow oscillations in 1 direction to pass through?
Polaroid sheet/polarising filter
What happens to all other oscillations when unpolarised waves are passed through a polarising filter?
Absorbed
Draw a diagram to represent what polarising filters do
(See notes)
What happens when a second polarising sheet is rotated when light is passing through it?
The intensity of light through it varies
How do we ensure maximum brightness with Polaroid sheets?
Line them up parallel
What happens to the brightness through a Polaroid sheet when 2 are lined up parallel?
Maximum brightness
What happens to the brightness through a second Polaroid sheet if they’re lined up perpendicular to each other?
Zero brightness (darkness)
How would we get zero brightness (darkness) through a second Polaroid filter?
Line it up perpendicular to the other one
definition of a progressive wave
a pattern of disturbances travelling through a medium and carrying energy with it
involves the particles of the medium oscillating in their equililbrium positions
definition of a progressive wave
a pattern of disturbances travelling through a medium and carrying energy with it
involves the particles of the medium oscillating in their equililbrium positions
Do waves with longer or shorter wavelengths bend the most?
Longer
What’s it important to make reference to when discussing progressive waves?
That it travels from one point in the medium to another
What happens in terms of phase with an increased distance from the source with progressive waves?
Phase lag steadily increases with distance from the source
Describe the energy in an unpolarised wave
All directions have the same energy
The energy in any component is 50% of the total
How do we work out the wavelength if we’re given the distance between, for example, 4 wavefronts?
Distance
—————
3
(Not 4 - draw it out and see that there’s 3 wavelengths)
What happens to the frequency and wavelength of waves as they travel from deep to shallow water and the propagation speed is less? Why?
Frequency status the same - the same number of waves pass any point (they haven’t been spontaneously created or destroyed)
Smaller wavelength (c = f x wavelength)
