Waves Flashcards
Define amplitude
The maximum displacement from equilibrium or rest position
Define frequency
Number of oscillations/vibrations at a point per unit time
Define phase difference
How far ‘out of step’ the oscillations at two points on the wave are
Explain wave interference
When two or more waves meet/superpose/overlap at a point there is a change in overall displacement
Explain what is meant by coherent waves
Constant phase difference/relationship between the waves
How do you know if two points on a wave are in phase?
Two points on a wave undergoing identical motion are in phase and have a phase difference of 0 °, 360 °, 720 ° etc
How do you know if two points on a wave are in antiphase?
Two points on a wave undergoing opposite motion are in antiphase and have a phase difference of 180 °, 540 ° etc
What can phase difference be measured in?
Number of wavelengths, radians or degrees
State the properties of progressive waves
- Progressive waves travel
- they have a speed
- they have a wavelength
- they have a frequency
- they have an amplitude
How do you identify a transverse wave?
The oscillation is at 90 ° to the direction of wave travel and the wave contains troughs and peaks
How do you identify a longitudinal wave?
The oscillation is parallel to wave travel and the wave contains areas of rarefaction and areas of compression
Give examples of transverse waves
Light, water, infrared and all EM
Give examples of longitudinal waves
Sound, ultrasound and pressure
Define plane-polarised light
Light that oscillates in one plane or direction only
What is the equation for intensity of a progressive wave?
Intensity = power/area, and since waves spread out symmetrically in 3D, the area grows as a sphere so
Intensity = P/4 πr^2
State the connection between intensity and amplitude
Intensity is directly proportional to amplitude^2
What diffraction occurs if the gap is smaller than the wavelength?
No diffraction
What diffraction occurs if the gap is bigger than the wavelength?
A little diffraction (curved edges)
When does maximum diffraction occur?
If the gap is about the same size as the wavelength
State the principal of superposition
If two or more waves meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual waves at that point
What are EM waves?
EM waves are oscillations in electric and magnetic fields. They are transverse, they all travel in a vacuum, and all travel at 3x10^8 m/s in empty space
Give the EM waves in order from largest to smallest wavelength
Radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays
What is the range of wavelengths for radio waves?
10^-1 to 10^6
What is the range of wavelengths for microwaves?
10^-3 to 10^-1
What is the range of wavelengths for infrared?
7x10^-7 to 10^-3
What is the range of wavelengths for visible light?
4x10^-7 (400nm) to 7x10-7 (700nm)
What is the range of wavelengths for ultraviolet?
10^-8 to 4x10^-7
What is the range of wavelengths for X-rays?
10^-13 to 10^-8
What is the range of wavelengths for gamma rays?
10^-16 to 10^-10
What is the equation for the refractive index (n)
n = speed of light in a vacuum/speed of light in the medium
State the equation that relates the angles between a light ray and the normal, and refractive indexes of two materials
nsinθ = k
n1sinθ1 = n2sinθ2
Explain how polarisers work
Polarisers block out a component of light passing through. Two crossed polarisers will block out both components. If one of the polarisers is rotated through 90 degrees, it will either reduce light passing through from max to min, or increase it from min to max.
State three potential phase differences in wavelengths, radians and degrees for two points on a wave in phase
1 wavelength, 2π radians, 360 degrees
2 wavelengths, 4π radians, 720 degrees
3 wavelengths, 6π radians, 1080 degrees
State three potential phase differences in wavelengths, radians and degrees for two points on a wave in antiphase
1/2 wavelength, π radians, 180 degrees
3/2 wavelengths, 3π radians, 540 degrees
5/2 wavelengths, 5π radians, 900 degrees
