Chapter 14~ Superposition Of Waves Flashcards
Definitions, key ideas 💡 and formulae
What is the principle of superposition of waves? 🌊
When 2 or more waves meet at a point, the resultant displacement is the algebraic sum of the displacements of the individual waves.
What is diffraction?
It is the spreading of a wave as it passes through a gap or around an obstacle.
Diffraction becomes more significant when…?
The size of the gap or obstacle is comparably or approximately equal to the wavelength of the wave. 🌊
Wavefronts (crests) are represented by lines so the wavelength is equal to ?
The distance between the two wave fronts
Diffraction is a wave effect that can be explained by :
The principle of superposition.
When interference occurs and the
Definition of interference :
It occurs when 2 waves of the same type (e.g. Both water 💦, sound 🔊, light 🚦, microwaves, etc.) occupy the same space.
It is also referred to as the formation of points of cancellation and reinforcement where two coherent waves 🌊 pass through each other.
What is constructive interference? 🚧
When do you get it according to the path difference?
When 2 waves reinforce to give increased amplitude.
For construction interference the path difference is whole numbers 🔢 of wavelengths :
Path difference = n♈
Definition of destructive interference?
And when do you get it according to path differences?
( n represents an integer 0,1,2,3, etc)
When two waves cancel to give reduced amplitude.
For destructive interference :the path difference is an odd number of half wavelengths.
Path differences = (n + 1/2)♈
Meaning of coherent
2 sources are coherent when they emit waves with a constant phase difference.
For an interference pattern to be observable the 2 overlapping waves must be…?
Coherent
Coherence refers to 2 characteristics being fulfilled, namely:
- The same frequency
2. A constant phase difference
Why if 2 waves are incoherent that they are not observable?
Their pattern will continually change to quickly for observations to be made.
What if the definition of phase difference?
The amount expressed in radians or degrees, by which one wave leads or lags another wave. 🌊 It is referred to the difference in the phases of 2 oscillating particles.
What is path difference?
It is the distance travelled by two waves, measured in metres or as a fraction of wavelength. It is the distance by which one wave leads or lags another wave.
It is the same as phase difference, only difference is the units.
Monochromatic means it have a single…
Wavelength
Name the 7 sub colours of the visible EM spectrum in order of decreasing wavelength.
They have differences of 0.5
E. G red is 7×10 ^-7 orange has the wavelength of 6.5 × 10^-7
Red, orange, yellow, green, blue, indigo and violet
Young’s double slit experiment :
Name the experiment details of the light source
Light source :
Monochromatic Light.
Can be achieved using a white light with a colour filter, or using monochromatic light sources, such a sodium lamp or Lazer
Bright 🔆 fringes are caused by?
And the path difference has to be..
Constructive interference.
Path difference = n♈
Dark fringes are caused by?
With the path difference of…
Destructive interference.
Path difference = (n + 1/2)♈
The double slit experiment can be used to determine the wavelength ♈ by the formula :
Also name what all the quantities stand for
♈ = ax / D
a- slit separation
x - fringe separation
D- Slit to screen distance
Explain the slit separation a -
This is the distance between the centre’s of the slits.
Fringe separation x refers to -
The distance between the centres of adjacent bright (or dark) fringes.
Slit- to-screen distance, D refers to?
This is the distance from the midpoint of the slits to the central fringe on the screen (where n=0).
What is a grating?
It is a series of close parallel slits
Mention one application of a diffraction grating
A spectrometer
When there are more than two slits you use what formula to workout the wave length?
n♈=dsin🎈
d- is the distance between adjacent slits
🎈- is the angle from the 0 order (n=0) to the 1st order (n=1)
The 4 comparisons of the use of a diffraction grating to determine wavelength compared with the Young 2-slit experiment :
- With a diffraction grating, the maxima are very sharp
- With a diffraction grating, the maxima are brighter 🔆 bec than the contributions of 2 slits, there are the contributions of many more slits.
- With 2 slits there is an inaccuracy in the measurement of the slit separation a. The fringes are also close together, so their separation may also be measured imprecisely
- Bec a diffraction grating has many more slits per cm, so d can be measured precisely.
Bec the maxima are widely spread, the angle 🎈 can also be measured to a higher degree of precision.
Therefore, a diffraction grating can be expected to give measurements of wavelengths to a much higher degree of precision than a simple double - slit arrangement.
