Unit 2.5: Wave properties Flashcards
Define Refraction
The change in direction of a wave at the boundary between two materials. This is caused by a change in speed.
Define Diffraction
The spreading of a wave when it meets an obstacle into regions where it would not be seen if it moved only in straight lines
Define reflection
As the waves strike a plane (flat) barrier they are reflected
What happens if waves are reflected off a curved barrier?
If a curved (concave) barrier such as a satellite dish is used, the waves can be made to converge (concentrate) at a point.
Do waves move slower in deep or shallow water?
The waves move more slowly in shallow water.
The frequency of
the waves remain constant and so the wavelength decreases.
Young’s Double slits: Does greater diffraction occur if there is a greater distance between the slits or smaller distance?
The smaller the distance between the slits, large diffraction occurs.
State the principle of superstition
The principle of superposition states if the waves from two sources occupy the same region then the total displacement at a point is the vector sum of the displacements of the individual waves at that point.
There are two types of interference, what are they?
Constructive and destructive
What is constructive interference?
If they arrive at a point in phase they will interfere constructively. If the two
incoming waves have the same frequency and equal amplitude A, the resultant wave produced by constructive interference has an amplitude 2A.
What is destructive interference?
If the two waves are out of phase that is they will interfere destructively. If the waves have equal
amplitude, the resultant wave has zero amplitude.
What is coherence?
To observe interference the two wave sources must be coherent and get a meaningful resultant wave by using the principle of superposition.
What is coherent?
there is a constant phase
difference. (They must therefore have the same
frequency)
What did Young’s double slit experiment prove?
That light travels as waves
What is path difference
A measure of the distance between two waves arriving at a point in
terms of their wavelength.
What is young’s double slit experiment
When interference from two coherent sources occurs a pattern of
bright and dark fringes appears
What can Young’s double slit experiment be used to determine?
The wavelength of light.
State the equation for Young’s slits experiment
λ=aΔy/D
λ=wavelength
a=distance between slits
Δy=fringe spacing
D=distance from the slits to the screen
What is a diffraction grating?
A diffraction grating is a plate on which there is a very large number of parallel, identical, very closely spaced slits. If monochromatic light is incident on this plate, a pattern of narrow bright fringes is produced.
Are Double slits the same as a diffraction grating?
Double slits are not the same as a diffraction grating
On a diffraction grating, what are bright fringes caused by?
Constructive
interference. Therefore,
at a bright point the phase
difference from the different slits is equivalent to an integer number of wavelengths
State the equation to calculate wavelength from a diffraction grating
nλ=dSinθ
d=slit width
n=order number
λ=wavelength
θ=angle
Why are the bright fringes usually further apart in a diffraction grating than Young’s slits?
Because there are so many slits, the bright fringes (or bands) are extremely narrow, and usually much
further apart (large ‘y’ since slit separation, ‘d’ is very small).
Explain Young’s double slit experiment
Two light sources at the double slits are
produced. Because these two light sources
originate from the same primary source,
they are coherent and create a sustained
and observable interference pattern of the dark and bright interference fringes.
During a Young’s double slits experiment, what causes bright fringes and what causes dark fringes?
Bright fringes=Constructive interference
Dark fringes=destructive interference
Diffraction grating with white light, what colour is diffracts the most and what colour diffracts the least?
Red light, because it has the longest wavelength in the spectrum, is diffracted through the largest angle.
Violet light has the lowest wavelength, and
is diffracted the least.
What is a stationary wave?
A stationary wave is a pattern of disturbances in a medium, in which energy is not propagated. The amplitude of particle oscillations is zero at equally-spaced nodes, rising to maxima at
antinodes, midway between the nodes.
How is a stationary wave created?
Stationary waves are produced from the superposition of two progressive
waves of equal amplitude and frequency, travelling in opposite directions.
On a stationary wave the amplitude at nodes are equal to what?
0
On a stationary wave the amplitude at antinodes is equal to what?
The maximum amplitude
A standing wave creates what musical note?
the 4th harmonic
Phase between the nodes is what?
Phase between the nodes is constant. Even though their amplitude is different.
What is the difference between each node?
½λ
Phase changes by pi at the nodes
