Chapter 11 and 12 - Waves Flashcards
What is a progressive wave?
An oscillation that travels through matter and transfers energy from one place to another.
What are radio waves used for?
Communication (TV and Radio)
What are microwaves used for?
Communications(Satellite, Mobile phones)
Cooking
What is infrared used for?
infrared cameras
electrical heaters
remote controls
What is visible light used for?
fibre optic communications
What is ultraviolet used for?
Sterilisation
What are Gamma waves used for?
Treating Cancer
What is diffraction?
When a wave passes through a gap that is a similar size to the wave’s wavelength, the wave will spread out
What is polarisation?
When a wave is made to oscillate along only one plane.
Why can’t longitudinal waves be polarised?
Longitudinal waves only oscillate in one direction (the direction of energy transfer)
Define intensity of a progressive wave
The radiant power passing through a surface, per unit area
What kind of relationship does intensity have with distance?
An inverse square relationship
Why does the amplitude of a wave get smaller the further it travels?
The further the wave travels the more spread out the energy of the wave becomes, this causes the intensity to of the wave to drop. Intensity is directly proportional to the amplitude squared so the amplitude also decreases.
What are the conditions for total internal reflection?
The light must be travelling through a medium with a higher refractive index than the material it meets at the boundary.
The angle the light hits the boundary must be greater than the critical angle.
What happens when light is travelling through a medium with a higher refractive index than the material it meets at the boundary and the angle the light hits the boundary is smaller than the critical angle?
refraction and partial reflection occurs.
What happens when light is travelling through a medium with a higher refractive index than the material it meets at the boundary and the angle the light hits the boundary is the critical angle?
The light refracts along the boundary
What is constructive superposition?
When two waves superimpose to create a wave with a greater amplitude.
What is destructive superposition?
When two waves superimpose to create a wave with a smaller amplitude.
What is coherence?
when two waves emitted from different sources have a constant phase difference, and therefore the same frequency.
What happens when two waves meet at a point with a phase difference of λ?
The waves are in phase and will constructively superimpose.
What happens when two waves meet at a point with a phase difference of 1/2 λ?
The waves are out of phase and will destructively superimpose.
How does a stationary wave form?
When a progressive wave is reflected directly backwards on to itself so that the two waves superimpose to create a new wave.
What is a node on a stationary wave?
A point of minimum displacement
What is an antinode on a stationary wave?
A point of greatest displacement
What is the fundamental frequency for a string?
The minimum frequency of a harmonic stationary wave on that string
The frequency of each harmonic of a string with two fixed ends is…
A multiple of the fundamental frequency
The frequency of each harmonic of a air column with one open end is…
(1/2n - 1/4) of the harmonic frequency
The frequency of each harmonic of a air column with two open ends is…
1/2n of the harmonic frequency
For a standing wave to form in an air column what must be at an open end?
An antinode
For a standing wave to form in an air column what must be at a closed end?
A node
Describe the set up for Young’s double slit experiment.
In front of a monochromatic source of light there is a single narrow slit, and in front of that there is a double slit, from there the light travels towards a screen.
Why is monochromatic light used in Young double-slit experiement?
So that the light arrives at the double slits in phase, as all of the waves of light have the same frequency.
State Young’s double slit experiment equation and what each symbol represents
Wavelength = (ax)/D
a - Separation between the double slits
x - Separation between fringes in the interference pattern
D - Distance between screen and slits
What did Young double-slit experiment prove?
The experiment demonstrates that light can form an interference pattern and so must be acting as a wave. As the waves must be superimposing to create bright and dark fringes.
What is special about the harmonics of a standing wave in a pipe with one open end?
There is only odd number harmoincs
Why do two polarising filters perpendicular to each other block all light?
The first filter blocks all light oscillating on the horizontal plane, so the light is oscillating vertically. When the light tries to pass through the next filter, it is blocked. As only light oscillating horizontally can pass through.
Why does light pass through two perpendicular polarising filters, with a diagonal filter in between them?
Light passing through the first filter is made to oscillate vertically. When it passes through the second filter, it is oscillating vertically but there is still a vertical and horizontal component of the light, so half of the light can pass through. When the light passes through the third filter, there is a horizontal component of the light, so half of the light can pass through.
What is the path difference of two waves?
The difference in wavelengths (measured in radians) between the distance travelled by the two waves.
How long is one wavelength measured in radians?
2pi
State the principle of superposition
When two or more waves meet at a point, the resultant displacement is equal to the sum of the displacement of each wave
State the law of reflection
The angle of incidence is equal to the angle of reflection
Whenever a wave refracts there is always some…
Partial reflection off the surface
If a wave slows down when it refracts it will…
Refract towards the normal
If a wave speeds up when it refracts it will…
Refract away from the normal
The greater the refractive index…
The slower light travels through the material
When total internal reflection happens, all…
light is reflected back into back into the original medium
How can the refractive index be found from the critical angle of a material?
Directing a ray of light through a semi-circular block so that the light enters the block 90 degrees to the boundary. The critical angle is between the normal and the ray of light in the block.
