Chapter 6 - Wave Behaviour

Question 1

Explain superposition.

Answer 1

When two or more waves meet, their displacements can be added together at every point. The principle of superposition states that when two or more waves overlap, the resultant displacement a given instance and position is equal the sum of the individual displacements that instance and position.

Question 2

What is wavelength on a displacement - displacement diagram?

Answer 2

The distance between any two points at the same part of the wave cycle.

Question 3

What is amplitude?

Answer 3

Maximum displacement of a wave from the equilibrium position.

Question 4

What is time period?

Answer 4

The time it takes to return to the same position in the wave cycle moving in the same direction.

Question 5

What is the equation for time period?

Answer 5

1 / f

Question 6

What is phase?

Answer 6

The stage in a wave cycle. When two points are at the same stage in a cycle they are in phase.

Question 7

What is phase difference?

Answer 7

The difference of points on a wave cycle, or the difference of phase of two waves at same point.

Question 8

What does in phase mean?

Answer 8

When two waves are doing the same thing at the same moment - no phase difference.

Question 9

What does in anti phase mean?

Answer 9

When two waves are doing exactly opposite things at the same moment - 180 degrees phase difference.

Question 10

What does out of phase mean?

Answer 10

When waves are neither in phase or anti phase.

Question 11

What is a phase angle?

Answer 11

Phase difference expressed in terms of 2pi radians or of 360 degrees. e.g. two waves which are half a cycle apart have a phase difference of pi or 180 degrees.

Question 12

What is a phasor?

Answer 12

Phasors are used to represent amplitude and phase in a wave. A phasor is a rotating arrow used to represent a sinusoidally changing quantity.

Question 13

What is the equation for phase angle (theta)?

Answer 13

2pif*t

Question 14

What is the equation for phase displacement? (a is radius)

Answer 14

a sin (2pif*t)

Question 15

What is a standing wave / stationary wave?

Answer 15

When two progressive waves of same frequency travel in opposite directions, the waves appear to stop moving. the nodes and antinodes appear to stay in the same place.

Question 16

What is an antinode?

Answer 16

A point on a wave where there is maximum amplitude.

Question 17

What is a node?

Answer 17

A point on a wave where there is zero amplitude.

Question 18

How far is the distance between adjacent nodes?

Answer 18

Half a wavelength.

Question 19

What is the equation for wavelength?

Answer 19

Wavelength (m) = wave velocity (m s^-1) / frequency (Hz)

Question 20

Describe nodes and antinodes in closed end tube and give an example.

Answer 20

There is a node at the closed end and an antinode at the open end. e.g. clarinet

Question 21

Describe nodes and antinodes in opened end tube and give an example.

Answer 21

There are antinodes at both ends e.g. flute

Question 22

What is refraction?

Answer 22

the fact or phenomenon of light, radio waves, etc. being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density.

Question 23

What is the refractive index?

Answer 23

A ratio of the speed of light in one medium to the speed of light in another medium.

Question 24

What is the equation for the refractive index of a material? (absolute refractive index)

Answer 24

speed of light in a vacuum / speed of light in material

Question 25

What is Snell’s Law?

Answer 25

The ratio sin i / sin r is th refractive index of the material.

Question 26

What is the normal?

Answer 26

A line drawn at 90 degrees to the surface of a transparent material.

Question 27

Which way does the light bend if the ray goes from a less dense medium to more dense medium?

Answer 27

Towards the normal.

Question 28

When is interference produced?

Answer 28

If two coherent waves overlap or if waves from a single source are divided and then reunited.

Question 29

What is path difference?

Answer 29

The difference in distance travelled by two or more waves from one point to another.

Question 30

When will waves meet in phase?

Answer 30

When their path difference = n*wavelength, when n is an integer.

Question 31

When will waves meet in anti phase?

Answer 31

When their path difference = (n + 1/2) * wavelength, when n is an integer.

Question 32

When are waves coherent?

Answer 32

When they have a clear constant phase difference. (Don’t have to be in phase)

Question 33

Describe constructive interference.

Answer 33

It occurs when waves meet in phase leading to a larger superposition amplitude (a maximum).

Question 34

Describe destructive interference.

Answer 34

It occurs when waves meet in anti phase leading to a lower superposition amplitude (a minimum)

Question 35

What is diffraction?

Answer 35

The spreading of waves after passing through a gap or past the edge of an obstacle. The spreading increases as the gap becomes narrower.

Question 36

What three things does diffraction not affect?

Answer 36

Wavelength, speed or frequency.

Question 37

Describe Young’s double slit experiment.

Answer 37

Where light is shone through two slits of distance d apart, onto a screen. Bright and dark fringes of light can be observed on a screen that the light is shone onto. Bright fringes occur where the two light paths meet in phase. Dark fringes occur when the two light paths meet in anti antiphase.

Question 38

What is the equation for path difference?

Answer 38

n * lamda = d sin(theta)

Question 39

What is the equation for wavelength in terms of slit separation (d), bright fringe spacing (x) and slit - screen distance (L)?

Answer 39

Lamda = xd / L

Question 40

What is the equation for line separation in metres of a diffraction grating?

Answer 40

1 / no. of lines per metre

Question 41

What is the equation for wavelength in single slit diffraction?

Answer 41

lamda = b sin(theta)

Question 42

If phasors make a complete circle what is the resultant phasor?

Answer 42

Zero.