Superposition

Question 0

Define coherence?

Answer 0

Two sources are coherent when they emit waves with a constant phase difference (and same frequency).

Question 1

What is the principle of superposition?

Answer 1

The total displacement of any point is equal to the sun of all the individual displacements at that point.

Question 2

What does stable interference mean?

Answer 2

Places of DI and CI remain fixed.

Question 3

At points of CI what are all the waves?

Answer 3

They are all in phase when they meet.

Question 4

At points of DI what are all the waves?

Answer 4

They are all in anti phase when they meet (pi out of phase).

Question 5

What happens if the freq is the same but the waves are out of phase?

Answer 5

You MAY still get a pattern.

Question 6

What happens if the phase relationship is changing?

Answer 6

The pattern will be unstable IF it appears at all.

Question 7

What happens if the waves have different amplitudes?

Answer 7

The pattern will be less clear because they won’t fully cancel each other out.

Question 8

Learn superposition with microwaves diagram.

Answer 8

In book.

Question 9

How do you find the wavelength of waves that are interfering on a wavefront diagram?

Answer 9

1) draw 2 lines - one from S1 and the other from S2, to the point A along an interference path.
2) measure the length of each line
3) if n=1 then the distance between the length of the lines is equal to wavelength (n=2, 2 wavelengths etc.)

Question 10

What is the point where the CI is present but the path difference is equal to 0?

Answer 10

The central maximum.

Question 11

What is the equation for path difference of CI and DI lines?

Answer 11

CI = nLambda
DI = (n+0.5)Lambda

Question 12

What are interference fringes?

Answer 12

The pattern of maxima and minima.

Question 13

Learn how to do superposition of sound waves.

Answer 13

In book.

Question 14

What are two problems with doing superposition with light?

Answer 14

1) White light contains multiple frequencies so not coherent waves (monochromatic source needed).
2) Light from a bulb is produced in bursts with random phase relationships.

Question 15

How do you set up an experiment for superposition of light?

Answer 15

Bulb - slit(in box) - double slit - filter

Question 16

Why use lasers for light superposition?

Answer 16

Monochromatic, brighter, more coherent.

Question 17

Look at diagrams on single/double slit light superposition.

Answer 17

Now.

Question 18

What is Youngs equation?

Answer 18

Look at diagram.
Lambda = ax/D

a is distance between sources
x is the distance between maxima
d is the distance between the source and the detector

Question 19

What does 2 slit interference with white light give?

Answer 19

Bright central max, spread either side of spectrum from violet through to red (furthest from CM), this is repeated. Happens because red light with longest lambda diffracts more than violet with shortest lambda.

Question 20

What problems arise when using the double slit experiment for superposition?

Answer 20

Inaccuracy is present in measuring lambda because the fringes tend to be blurry, which makes it hard to measure X.

Question 21

Why do diffraction gratings work better than double slits when doing superposition of light?

Answer 21

They give clearer peaks and troughs with wider gaps.

Question 22

When measuring θ for light that has gone through a diffraction grating, what equation should be used?

Answer 22

nLambda = dSinθ
n is order of maximum
d is the spacing between the slits

Question 23

What are uses of light superposition?

Answer 23

Sharper brighter maxima

Better accuracy in measuring slit separation because θ is more accurate than X.

Question 24

Explain how a stationary wave is formed in a tube?

Answer 24

1) the incident wave is reflected at the closed end of the tube.
2) the reflected wave interferes with the incident wave
3) this produces a resultant wave with nodes and antibodies