Topic 5 Flashcards
What is the difference between mechanical and electromagnetic waves?
Mechanical waves require a medium through which to travel whereas electromagnetic waves do not.
Definition: Amplitude
The maximum displacement of particles from their undisturbed position.
Definition: (Time) Period
The time for one complete cycle or oscillation of the wave.
Definition: Wavelength
The distance between corresponding points on successive cycles of the wave.
Definition: Frequency
The number of cycles of the wave passing through a point in the medium in one second. (Hz)
Equation: Frequency
f = 1/ T
f = frequency (Hz)
T = ‘time’ period (s)
Equation: Wavespeed *
v = fλ
v = wavespeed (ms-1)
f = frequency (Hz)
λ = wavelength (m)
Definition: Longitudinal waves
The direction of oscillation is parallel to the direction of travel of wave energy, due to a series of compressions and rarefactions.
Definition: Transverse wave
The direction of oscillation is perpendicular to the direction of travel of wave energy.
What is an example of a longitudinal wave?
Sound
What is an example of a transverse wave?
Ripples in water
Definition: Principle of superposition
When two or more waves meet, the total displacement of the standing wave is the sum of the individual displacements.
How is a standing wave formed?
When two coherent waves interfere with each other and their displacements add together to form a standing wave.
What does the fundamental node look like?
Definition: Wavefront
A line joining all points in a medium where the waves are in phase.
Definition: Coherent waves
Waves which have.. 1) the same frequency 2) similar amplitudes 3) an unchanging phase relationship 4) If the same type
Definition: Constructive interference
The interference between two waves which occurs when they are exactly in phase, creating maximum displacement of the standing wave at this point.
Definition: Destructive interference
The interference between two waves which occurs when they are in antiphase, creating minimum displacement of the standing wave at this point.
Equation: Velocity of transverse wave on a string *
v = √(T / μ)
v = velocity (ms-1)
T = tension (N)
μ = mass per unit length (kgm-1)
How do sound waves travel through air?
Air molecules vibrate parallel to the direction of travel of the wave producing a series of compressions and rarefactions.
What is the speed of radio signals?
The same as the speed of light. (3.00x10⁸ ms⁻¹)
How is an interference pattern produced?
1) Two coherent waves are produced or a wave is reflected back on itself. 2) The waves interfere with each other resulting in superposition occurring. 3) Where the waves are exactly in phase, maximum constructive interference will occur and there will be maximum amplitude. 4) Where the waves are in antiphase, maximum destructive interference will occur and there will be minimum amplitude.
In what situation will a minima never reach zero?
If the waves have different amplitudes.
Why is coherence necessary for an interference pattern to be produced?
So that waves have a constant wave difference and will therefore be exactly in phase or antiphase with each other at different points.
How can the range of pulse-echo techniques be increased?
Increase the pulse duration.
How can the resolution of pulse-echo techniques be increased?
Decrease the wavelength so that there is less diffraction.
Equation: Ultra-sound
s = vt / 2
s = distance of object from transmitter (m)
v = speed of sound in medium (ms-1)
t = time taken for wave to reach object and return back to transmitter (s)
What type of wave is ultrasound?
Longitudinal wave.
Why should pulses be produced in pulse-echo techniques?
So that you can distinguish which reflected pulse corresponds to which emitted pulse.
What should you do when using pulse-echo calculations?
Divide by 2 as it is the time taken to reach the object and return.
What is the difference between polarised and unpolarised light?
In unpolarised light, oscillations take place in every plane, which are all perpendicular to the direction of wave travel. Plane-polarised light has oscillations in one plane only.
Why can’t sound waves be polarised?
They are longitudinal waves.
What is a natural source of polarised light?
Reflected light / glare.
How do polaroid glasses work?
They filter at 90 degrees to the already polarised reflected light, meaning all of the light is absorbed.
