Chapter 14~ Superposition Of Waves

Question 1

What is the principle of superposition of waves? 🌊

Answer 1

When 2 or more waves meet at a point, the resultant displacement is the algebraic sum of the displacements of the individual waves.

Question 2

What is diffraction?

Answer 2

It is the spreading of a wave as it passes through a gap or around an obstacle.

Question 3

Diffraction becomes more significant when…?

Answer 3

The size of the gap or obstacle is comparably or approximately equal to the wavelength of the wave. 🌊

Question 4

Wavefronts (crests) are represented by lines so the wavelength is equal to ?

Answer 4

The distance between the two wave fronts

Question 5

Diffraction is a wave effect that can be explained by :

Answer 5

The principle of superposition.

Question 6

When interference occurs and the

Definition of interference :

Answer 6

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.

Question 7

What is constructive interference? 🚧

When do you get it according to the path difference?

Answer 7

When 2 waves reinforce to give increased amplitude.

For construction interference the path difference is whole numbers 🔢 of wavelengths :

Path difference = n♈

Question 8

Definition of destructive interference?
And when do you get it according to path differences?
( n represents an integer 0,1,2,3, etc)

Answer 8

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)♈

Question 9

Meaning of coherent

Answer 9

2 sources are coherent when they emit waves with a constant phase difference.

Question 10

For an interference pattern to be observable the 2 overlapping waves must be…?

Answer 10

Coherent

Question 11

Coherence refers to 2 characteristics being fulfilled, namely:

Answer 11

1. The same frequency

2. A constant phase difference

Question 12

Why if 2 waves are incoherent that they are not observable?

Answer 12

Their pattern will continually change to quickly for observations to be made.

Question 13

What if the definition of phase difference?

Answer 13

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.

Question 14

What is path difference?

Answer 14

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.

Question 15

Monochromatic means it have a single…

Answer 15

Wavelength

Question 16

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

Answer 16

Red, orange, yellow, green, blue, indigo and violet

Question 17

Young’s double slit experiment :

Name the experiment details of the light source

Answer 17

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

Question 18

Bright 🔆 fringes are caused by?

And the path difference has to be..

Answer 18

Constructive interference.

Path difference = n♈

Question 19

Dark fringes are caused by?

With the path difference of…

Answer 19

Destructive interference.

Path difference = (n + 1/2)♈

Question 20

The double slit experiment can be used to determine the wavelength ♈ by the formula :

Also name what all the quantities stand for

Answer 20

♈ = ax / D

a- slit separation
x - fringe separation
D- Slit to screen distance

Question 21

Explain the slit separation a -

Answer 21

This is the distance between the centre’s of the slits.

Question 22

Fringe separation x refers to -

Answer 22

The distance between the centres of adjacent bright (or dark) fringes.

Question 23

Slit- to-screen distance, D refers to?

Answer 23

This is the distance from the midpoint of the slits to the central fringe on the screen (where n=0).

Question 24

What is a grating?

Answer 24

It is a series of close parallel slits

Question 25

Mention one application of a diffraction grating

Answer 25

A spectrometer

Question 26

When there are more than two slits you use what formula to workout the wave length?

Answer 26

n♈=dsin🎈

d- is the distance between adjacent slits

🎈- is the angle from the 0 order (n=0) to the 1st order (n=1)

Question 27

The 4 comparisons of the use of a diffraction grating to determine wavelength compared with the Young 2-slit experiment :

Answer 27

1. With a diffraction grating, the maxima are very sharp
2. With a diffraction grating, the maxima are brighter 🔆 bec than the contributions of 2 slits, there are the contributions of many more slits.
3. 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
4. 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.