Module 4 - Waves (Superposition)

Question 1

What is the principle of supeposition

Answer 1

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

Question 2

What is constructive interference

Answer 2

when the resultant wave has a greater amplitude that the original waves

Question 3

When is there perfect constructive interference

Answer 3

When the 2 waves superpose whilst in phase

Question 4

What is destructive interference

Answer 4

When the resultant wave has a smaller displacement than the original waves

Question 5

When is there perfect destructive interference

Answer 5

• When the two waves superpose in antiphase

Question 6

What magnitude of path difference will cause perfect constructive interference and why

Answer 6

ΔL = nλ, where lambda is an integer, this is because both waves will be in phase when they superpose

Question 7

What magnitude of path difference will cause perfect destructive interference

Answer 7

ΔL = (n + 0.5) λ, where lambda is an integer, this is because both waves will be in antiphase when they superpose

Question 8

What is meant by coherent waves

Answer 8

• Waves that have a constant phase difference

Question 9

What wave features must two waves have to be coherent

Answer 9

• Constant phase difference
• The same frequency
• The same wavelength

Question 10

What is meant by a stable interference pattern

Answer 10

• A superposition pattern that remains the same during the time of interference

Question 11

What is the setup of the Double slit experiment

Answer 11

• A coherent light source is shone through double slit, in a darkened room

Question 12

How is a coherent light source generated

Answer 12

• Monochromatic light that is diffracted through a single slit

Question 13

Describe the action of the waves as they diffract through the double slit

Answer 13

• 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

Question 14

What is the Double slit equation

Answer 14

λD = ax
λ - wavelength
D - distance from the screen
a - slit spacing
x - fringe spacing

Question 15

When measuring the fringe spacing what can you do to reduce the percentage uncertainty and why

Answer 15

-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

Question 16

What is the equation for fringe spacing

Answer 16

x = L/ n-1,
L - length from the center of one fringe to the center of another
n - the number of fringes measured

Question 17

What is the relationship between the intensity and the order of the maxima

Answer 17

• As the order of the maxima increases the intensity of the wave decreases

Question 18

What is meant by the fringes on the screen

Answer 18

The regions of maxima where constructive interference occurs

Question 19

What is the relationship between the fringe spacing and the distance from the central maxima

Answer 19

As the distance from teh central maxima increases the fringe spacing stays constant

Question 20

How do you determine the wavelength of light from YDS experiment

Answer 20

• Measure fringe spacing for varying distances from the screen
• Draw a graph of x/D
  -Multiply the gradient by the slit seperation

Question 21

what is path difference

Answer 21

The difference in the distance travelled by two waves from their source to a specific point

Question 22

What is meant by phase difference

Answer 22

The difference in degrees or radians of oscillations on the same or different waves