Module 4 - Waves (Superposition) Flashcards
What is the principle of supeposition
When two waves meet at a point, they interfere and the resultant displacement is equal to the sum of the vector displacements of the individual waves
What is constructive interference
when the resultant wave has a greater amplitude that the original waves
When is there perfect constructive interference
When the 2 waves superpose whilst in phase
What is destructive interference
When the resultant wave has a smaller displacement than the original waves
When is there perfect destructive interference
- When the two waves superpose in antiphase
What magnitude of path difference will cause perfect constructive interference and why
ΔL = nλ, where lambda is an integer, this is because both waves will be in phase when they superpose
What magnitude of path difference will cause perfect destructive interference
ΔL = (n + 0.5) λ, where lambda is an integer, this is because both waves will be in antiphase when they superpose
What is meant by coherent waves
- Waves that have a constant phase difference
What wave features must two waves have to be coherent
- Constant phase difference
- The same frequency
- The same wavelength
What is meant by a stable interference pattern
- A superposition pattern that remains the same during the time of interference
What is the setup of the Double slit experiment
- A coherent light source is shone through double slit, in a darkened room
How is a coherent light source generated
- Monochromatic light that is diffracted through a single slit
Describe the action of the waves as they diffract through the double slit
- The waves superpose to create a stable interference pattern
- The stable interference patterns have regions of maxima and minima where there is constructive and destructive interference respectively
What is the Double slit equation
λD = ax
λ - wavelength
D - distance from the screen
a - slit spacing
x - fringe spacing
When measuring the fringe spacing what can you do to reduce the percentage uncertainty and why
-Measure the length of multiple fringes, and then divide by the number of fringes measured, because one fringe will have a length in the order of millimeters, meaning that the uncertainty using a ruler would be high
What is the equation for fringe spacing
x = L/ n-1,
L - length from the center of one fringe to the center of another
n - the number of fringes measured
What is the relationship between the intensity and the order of the maxima
- As the order of the maxima increases the intensity of the wave decreases
What is meant by the fringes on the screen
The regions of maxima where constructive interference occurs
What is the relationship between the fringe spacing and the distance from the central maxima
As the distance from teh central maxima increases the fringe spacing stays constant
How do you determine the wavelength of light from YDS experiment
- Measure fringe spacing for varying distances from the screen
- Draw a graph of x/D
-Multiply the gradient by the slit seperation
