Superposition

Question 1

What is Superposition?

Answer 1

It is when two or more waves of the same type meet it superpose in space, and the resultant displacement at any point if space and time is the vector sum of all individual displacements at that point.

Question 2

How can a resultant wave be represented?

Answer 2

The vector sums of the waves at different points is added up and plotted in a new graph.

Question 3

What are stationary waves?

Answer 3

Waves that do not transfer energy. The energy is stored in the oscillations of the medium.

Question 4

How are stationary waves formed?

Answer 4

By the superposition if two progressive waves of equal amplitude And frequency Travelling in opposite directions.

Question 5

What are nodes?

Answer 5

Points on a stationary wave where the displacement is always 0.

Question 6

_____ of vibration of neighbouring particles in stationary waves are not the same unlike progressive waves

Answer 6

Amplitude

Question 7

What are antibodies?

Answer 7

They are the points with maximum amplitude.

Question 8

At any instant, all points in a stationary wave between two adjacent nodes are _____ and _____ with all points between the next pair of adjacent nodes.

Answer 8

In phase, anti-phase

Question 9

What is the wavelength in a stationary wave?

Answer 9

It is 2x the does ration between Teo nodes or antinodes.

Question 10

What happens to a wave when reflected at a hard surface?

Answer 10

It’s phase shifts by half π

Question 11

What happens when a wave is reflected at a soft surface?

Answer 11

No phase shift occurs.

Question 12

When waves are reflected at 90 degrees

Answer 12

Stationary waves are formed as the reflected wave would be of equal frequency and magnitude and Travelling in the opposite direction.

Question 13

In a cylinder with one end open, there is always an ______ when the wave is reflected at the closed end. Thus the length of the air column is always ______.

Answer 13

Node. Slightly shorter than x/4 π wavelengths.

Question 14

In a cylinder with both ends open, there is always an ______ when the wave is reflected at the open end. Thus the length of the air column is always ______.

Answer 14

Antinode. Slightly shorter than x/2 π wavelengths.

Question 15

Why are oscillation nodes pressure antinodes for a stationary wave?

Answer 15

E.g sound waves: Because ar that point air particles do not move at that point but pressure variation is the greatest because in one part of the wave particles move towards it thus pressure is high, while in another part of the wave particles move away from it thus pressure is Low.

Question 16

Why are oscillation antinodes pressure nodes?

Answer 16

Pressure variation is the least as particles are vibrating with maximum amplitude while their relative separations do not vary much.

Question 17

What is diffraction?

Answer 17

It is the bending of waves found the edges of gaps or objects, spreading into a region where a geometrical shadow might be expected.

Question 18

Diffraction is more pronounced when _____.

Answer 18

The size of the gap is small or close to the wavelength of the wave.

Question 19

What is interference?

Answer 19

It is the result of superposing to or more waves of the same type.

Question 20

When two waves of the same frequency and amplitude supervise in phase, they ______. What is the new amplitude?

Answer 20

They reinforce each other and the resultant displacements are twice that of each individual wave. I is 4x the initial I. I is directly proportional to A^2. This is a constructive interference.

Question 21

When two waves of same frequency and amplitude superpose in anti phase, what is the resultant wave?

Answer 21

0. They cancel each other out. This is destructive interference.

Question 22

What are coherent waves?

Answer 22

The phase difference is constant, implying that frequency is same.

Question 23

What are the conditions for interference patterns to be observable, besides the condition that they must superpose?

Answer 23

They must be coherent.
They must have (approximately) the same amplitude so there can be constructive/destructive interference.
Transverse waves must either be unpolarised or polarised in the same plane.

Question 24

In young’s double slit experiment, bright lines on the screen are regions of _____ interference, where path difference is _____ wavelengths. Dark lines are regions of _____ interference where path difference is _____ wavelengths.

Answer 24

Constructive, x, destructive , 2x+1/2

Question 25

For young’s double slit experiment relate wavelength to double slit separation a, fringe spacing x and distance D from the double slit.

Answer 25

λ=ax/D

Question 26

Briefly state the derivation of λ=ax/D.

Answer 26

Sinθapprox=tanθ when θ is very small.

Sinθ=λ/a=tanθ=x/D

Question 27

Why does light intensity decrease with distance from center?

Answer 27

The angle of diffraction at the slugs increases so light intensity decreases. I=Iinitialcosθ

Question 28

How can the contrast of the cringes be increased?

Answer 28

Increase intensity of incident light
Decrease distance D
More slits.

Question 29

What are the factors affecting fringe patterns?

Answer 29

Monochromatic light
Incident light on slits should have no phase difference.
Screen should be parallel to slits.

Question 30

How are the angle of separation of bright bands θ, order of bright band from the centre n, wavelength λ and slit separation d related?

Answer 30

dsinθ=nλ

Question 31

How do we know light is a wave?

Answer 31

Light diffracts and an interference pattern are observed. Both are characteristics of wave motion.