11,12. Waves (4.4)

Question 1

What is a progressive wave? (2)

Answer 1

• a transfer of energy
• as a result of oscillations

(A wave which travels continuously in a medium in the same direction without a change in its amplitude)

Question 2

Longitudinal vs transverse

Answer 2

• L has oscillations parallel to direction of energy transfer
• T has oscillations perpendicular to direction of energy transfer

Question 3

What is the displacement of a wave?

Answer 3

the relative change in position of a wave as it traveled through a medium.

Question 4

amplitude

Answer 4

The amplitude is the perpendicular distance from the centre line to the peak of the wave

Question 5

wavelength

Answer 5

The length travelled in one full wave in the direction of energy transfer

Question 6

wave period

Answer 6

The time it takes for two successive peaks (one wavelength) to pass a specified point

Question 7

Phase difference

Answer 7

The phase difference is the difference in the phase angle of the two waves.

(How many degrees apart they points if the wave are apart should the wave be turned into a sin/cos function)

Question 8

Frequency

Answer 8

How many peaks of a wave pass one point in one second

Question 9

Wave speed (and equation)

Answer 9

Wave speed is the distance a wave travels in a given amount of time

v = f λ

Question 10

Wavefront

Answer 10

Lines of constant phase (which are perpendicular to the direction of energy transfer)

Question 11

What does a change in wavefronts signify?

Answer 11

Some wave phenomenon

Question 12

Reflection

Answer 12

When a wave reverses direction upon meeting the boundary between two different media.

Question 13

Angle of incidence (i) vs angle of refraction (r) of a reflected wave

Answer 13

i = r

Question 14

What does the distance between wavefronts represent?

Answer 14

Wavelength

Question 15

Refraction

Answer 15

When a wave changes speed (and usually direction) upon crossing the boundary between two different media.

Question 16

Does f or λ change during refraction?

Answer 16

λ

Question 17

What is the relationship between change in speed and angle of refraction relative to the normal?

Answer 17

• if speed decreases, bends towards normal
• if speed increases, bends away from normal

Question 18

When do sound waves speed up during refraction

Answer 18

If they go into physically denser media

Question 19

When do EM waves speed up in refraction?

Answer 19

When they go into less optically dense media

Question 20

Is physical density proportional to optical density

Answer 20

Not always

Question 21

Diffraction

Answer 21

Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture.

Question 22

What is polarisation?

Answer 22

A property of only transverse waves which defines the plane of oscillation of the wave

Question 23

What is the plane of alignment of a polarising filter?

Answer 23

The plane in which it will allow oscillations.

Question 24

When travelling through a filter, what happens to the intensity of an unpolarised wave?

Answer 24

It halves

Question 25

Relationship between intensity and amplitude

Answer 25

I is directly proportional to A^2

Question 26

Relationship between intensity, power, area:

Answer 26

I =P/A

Question 27

Order of EM wavelength from longest to shortest:

Answer 27

* radio * micro * infrared * visible * UV * X-ray * gamma

Question 28

Radiowave λ (m)

Answer 28

10^-1 - 10^6

Question 29

Microwave λ (m)

Answer 29

10^-3 - 10^-1

Question 30

Infrared λ (m)

Answer 30

7x10^-7 - 10^-3

Question 31

Visible light λ (m)

Answer 31

4x10^-7 - 7x10^-7

Question 32

UV λ (m)

Answer 32

10^-8 - 4x10^-7

Question 33

X-ray λ (m)

Answer 33

10^-13 - 10^-8

Question 34

Gamma λ (m)

Answer 34

10^-16 - 10^-10

Question 35

Which 2 EM waves have an overlap of λ?

Answer 35

Gamma and X-ray

Question 36

refractive index formula

Answer 36

n = c/v

Question 37

Refractive index definition

Answer 37

The ratio between the speed of light in a vacuum to the speed of light in the medium

Question 38

Snell’s law equation

Answer 38

n1sinθ1=n2sinθ2

Question 39

What is the critical angle

Answer 39

The angle where total internal reflection occurs

Question 40

Total internal reflection

Answer 40

When light completely reflects back at a boundary between two media as opposed to transmitting across the boundary and refracting.

Question 41

Critical angle formula

Answer 41

sinC = 1/n (when the other medium is air) General formula: sinC = n2/n1

Question 42

Conditions for total internal refraction:

Answer 42

1. n1>n2 2. i>=iC

Question 43

What is the definition of superposition?

Answer 43

When two waves meet at a point, the resultant displacement is equal to the sum of the displacements of the individual waves.

Question 44

PAG 5

Question 45

Interference

Answer 45

In physics, interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have greater amplitude or lower amplitude if the two waves are in phase or out of phase, respectively. When two coherent waves superpose.

Question 46

Constructive interference

Answer 46

Larger amplitude

Question 47

Destructive interference

Answer 47

Smaller amplitude

Question 48

Coherence

Answer 48

Two waves have a constant phase difference (so same frequency and wavelength)

Question 49

Path difference

Answer 49

The difference in length in the paths travelled by each of the waves that interfere

Question 50

Phase difference (in terms of two dif waves)

Answer 50

The cycle difference between two coherent waves at the same point

Question 51

Path difference and phase difference of constructive interference

Answer 51

* PLD = multiple of wavelength * Phase difference = multiple of 2pi

Question 52

Path difference and phase difference of destructive interference:

Answer 52

* PLD = odd multiple of (wavelength/2) * Phase dif = odd multiple of pi

Question 53

What did Young’s double slit experiment show about the nature of light?

Answer 53

It showed that light has wave nature.

Question 54

What is Young’s double slit equation?

Answer 54

λ = (ax)/D where a = distance between slits, x = distance between consecutive fringes/bright spots, D = horizontal distance between slits and wall

Question 55

Remember how a stationary wave looks.

Question 56

Similarities between stationary and progressive waves:

Answer 56

* both are comprised of oscillations * both have wavelength, frequency, amplitude

Question 57

Differences between stationary and progressive waves:

Answer 57

* progressive has energy transfer in direction of wave, stationary has no net energy transfer * wavelength of stationary =2 x distance between two adjacent nodes but wavelength of oregressive is distance between two points in phase * all points between two nodes are in phase for stationary but the phase changes across one complete cycle of the wave for progressive * in prigressive all points have same amplitude, in stationary max amplitude accurs at antipode and drops to 0 at node

Question 58

Node

Answer 58

A point where there is 0 displacement in a stationary wave

Question 59

Antinode

Answer 59

A point in a stationary wave where there is maximum displacement

Question 60

Draw out first 5 harmonics, with expressions for λ, of a stationary wave on a string fixed at both ends

Answer 60

Textbook 235

Question 61

Draw out first 4 harmonics (and wavelength) of a stationary wave in an open tube

Answer 61

Textbook 239

Question 62

Draw out first 5 harmonics (and expressions of wavelength) for a stationary wave in a tube with only one side open

Answer 62

Textbook 237