Waves Flashcards
What is a progressive wave?
A wave that transfers energy from a source through the surroundings by means of oscillations.
What is a transverse wave?
A wave where vibrations are at 90 degrees to the direction of energy transfer.
What is displacement of a wave?
The distance of a point on a wave above or below the mean position at any time.
What is amplitude?
The maximum displacement of the wave from the mean position.
What is wavelength?
The distance between two adjacent points in phase.
What is a longitudinal wave?
A wave where vibrations are parallel to the direction of energy transfer.
What is time period?
The time taken for one complete oscillation or wavelength.
What is frequency?
The number of wavelengths per unit time.
What wave phenomena can transverse waves experience?
Reflection, refraction, diffraction, interference, polarisation
What wave phenomena can longitudinal waves experience?
Reflection, refraction, diffraction, interference
What is phase difference?
How much one wave lags behind another as an angle in degrees or radians.
What is the definition of intensity for a progressive wave?
The radiant power passing through a surface per unit area.
What 2 things is intensity proportional to?
1 / distance from the source^2
Amplitude^2
What is the order of waves from biggest to smallest?
Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
What is diffraction?
When waves pass through a gap or around an obstacle and spread out into the space beyond.
When does maximum diffraction occur?
When the wavelength of the source is equal to the gap through which it is diffracting.
What is polarised light?
Light waves in which the vibrations occur in a single plane at 90 degrees to the direction of wave energy transfer.
What is refraction?
The change in speed of a wave when it passes from one medium to another. There is usually a change in direction as well.
What is the definition of refractive index?
The ratio of the speed of light in a vacuum to the speed of light in a medium.
What happens to a ray of light when it moves from a less dense to a more dense medium?
The ray of light is refracted towards the normal so the angle of incidence > the angle of refraction.
The ray of light slows down in the denser medium and its wavelength decreases because its frequency stays the same.
What things must be true for total internal reflection to take place?
The ray of light is travelling from a more dense to a less dense medium, the ray of light speeds up and bends away from the normal, the angle of incidence > critical angle.
What is the definition of a critical angle?
When the angle of incidence is C, the angle of reflection is 90 degrees.
What is total internal reflection?
When the angle of incidence is greater than the critical angle then all the light reflects at the boundary.
What is the principle of superposition?
When two similar types of waves meet at a point, the sum of their individual displacements is equal to the displacement of the resultant wave.
What is path difference?
The difference in distance from one source to the detector compared with the other source to the detector.
What is interference?
Superposition of two progressive waves from coherent sources to produce a resultant wave with displacement equal to the sum of the individual displacements of the two waves.
What is coherence?
When two waves are emitted with a constant phase difference, same frequency, polarised in the same plane and similar amplitude.
What is destructive interference?
When two waves meet exactly in antiphase, the amplitudes cancel to produce no peaks or troughs.
What is constructive interference?
When two waves meet exactly in phase, the amplitudes add up to produce large peaks and troughs.
What does each symbol represent in the equation λ=ax/D
λ - wavelength
a - slit separation
x - fringe separation which is the distance between 2 adjacent bright fringes.
D - distance between the slits and screen
What must be true for λ=ax/D to be useable?
a must be much smaller than D (a«D)
The two sources must be coherent
How are standing waves produced?
As a result of superposition of two progressive waves with the same amplitude and frequency, travelling at the same speed but in opposite directions meet and undergo superposition producing nodes and antinodes.
What is an antinode?
Where two waves interfere constructively and produce a wave of maximum amplitude.
What is a node?
Where two waves interfere destructively and produce a wave with zero displacement.
What is the distance between two adjacent nodes or two adjacent antinodes?
λ/2
What is the distance between a node and antinode?
λ/4
How does energy transfer in progressive waves differ to in standing waves?
In progressive waves energy is transferred in the direction of the wave.
In standing waves energy is trapped between the source and reflector.
How does wavelength in progressive waves differ to in standing waves?
In progressive waves wavelength is the minimum distance between two adjacent points oscillating in phase.
In standing waves wavelength is twice the distance between adjacent nodes.
How does phase difference in progressive waves differ to in standing waves?
In progressive waves phase changes across the complete cycle of the wave.
In a standing wave between two adjacent nodes all particles are in phase. On the opposite side of the node all particles are in antiphase.
How does amplitude in progressive waves differ to in standing waves?
In progressive waves amplitude is the same for all particles.
In standing waves amplitude varies from zero at the nodes to maximum at the antinodes.
What is monochromatic light?
Monochromatic is light with a single wavelength or frequency.
What are harmonics?
Certain frequencies where standing waves are set up. Harmonics are whole number multiples of the fundamental frequency.
What is the equation for path difference?
S1P -S2P
How would you measure the slit separation?
Use a travelling microscope
