Yr 12 - Waves (2 of 2)

Question 1

Order of EM spectrum (starting with largest wavelength & smallest Frequency)

Answer 1

• Radio
• Micro
• Infrared
• Visible
• Ultraviolet
• X-Rays
• Gamma

Question 2

Wavelengths for each em wave starting with greatest

Answer 2

• Radio 10^5
• Micro 10^-1
• Infrared 10^-3
• Visible 8x10^-7
• Ultraviolet 4x10-7
• X-rays 10^-8
• Gamma 10^-12

All in meters

Question 3

Frequencies for each em wave starting with the lowest.

Answer 3

• Radio 10^3
• Micro 10^8
• Infrared 10^12
• Visible 10^15
• Ultraviolet 10^16
• X-Rays 10^18
• Gamma 10^20

All in hertz

Question 4

Which type of waves can be polarised?

Answer 4

Transverse Waves only.

Longitudinal already in 1 plane.

Question 5

What would a arrow diagram of each wave be like:

• Polarised wave
• Unpolarised

Answer 5

• Arrow pointing in one straight direction only
• Arrows pointing in every direction

Question 6

Which type of waves used for thermal imagery & by rattlesnakes?

Answer 6

Infrared

Question 7

Why is there a glare on a large body of water when the sun is shining?

Answer 7

• Light from sun is unpolarised
• When light hits water it is polarised
• Some light is refracted into the water and the rest is reflected off the water.
• Light reflected is polarised & glares due to high intensity in one plane.

Question 8

What is a plane polarised wave?

Answer 8

A traverse wave oscillating in 1 plane.

Question 9

What is the refractive index?

Answer 9

Ratio of speed of light in vacuum to speed in a substance.

Question 10

Describe why a light wave refracts away/to from the normal the moving into a substance.

Answer 10

Less -> more dense
- Towards normal as wave hits substance at an angle and the side of wave that contacts first is slowed and therefore the wave (bends).

More -> less dense
- Away from normal (vice versa)

Think about it as a car going off-road at an angle

Question 11

What is snells law?

Answer 11

n Sin𝞡 = constant

n sin(AOI) = n sin (AOR)

AOI = Angle of Incidence
AOR = Angle of refraction

Question 12

Where are AOR & AOI measured from?

Answer 12

Both are measured from the normal

Question 13

What is total internal reflection & when does it occur (angles)

Answer 13

Reflection of all light back into original medium

• Occurs when AOI is greater than C
• When AOI = C light directed along boundary

C = critical angle

Question 14

What is an alternative (but similar) equation:

Sin C = 1 / n

Answer 14

Sin C = n2 / n1

Question 15

What happens when light travels into:

• Lower n
• Higher n

Answer 15

• Faster
• Slower

Question 16

Critical Angle

Answer 16

AOI that produces AOR of 90°

Question 17

What trait of a wave causes n to vary?

Answer 17

Frequency of the wave

Question 18

What is dispersion

Answer 18

Process of splitting white light
- Occurs due to varying wavelengths
- Shorter wavelength = greater dispersion (violet)

This is why different colours of light diffract less/more

Question 19

What is constructive interference

Answer 19

When 2 waves superpose in phase

Question 20

What is destructive interference

Answer 20

When 2 waves superpose in anti phase

Question 21

What is superposition? (Same as principle of superposition)

(superimposition is the same thing but less sciencey)

Answer 21

When 2 or more waves meet at a point & resultant amplitude is vector sum of individual amplitude.

Question 22

What is coherent?

Answer 22

2 or more waves that have:

• Same wavelength
• Constant phase difference
• Same frequency

They do not have to be in phase.

Question 23

What is phase difference?

Answer 23

Fraction of a cycle between the same point on 2 different waves.

Question 24

What is path difference?

Answer 24

Difference in distance travelled by 2 coherent waves from different sources to a distinct point.

Question 25

Do waves have to be coherent to interfere?

Answer 25

Yes

Question 26

Can transverse and longitudinal waves interfere with each other?

Answer 26

Yes

Question 27

Explain Youngs double slit experiment including the key terms.

Answer 27

-> Slit separation = gap between slits next to light source -> Separation distance = Distance between slit and screen -> Fringe separation = distance between constructive fringes (Bright fringes)

Question 28

How and where to do measure fringe separation during Youngs double slit?

Answer 28

Measured from central fringe (N=0) then (N= +/- 1 etc) Distance between constructive fringes. (bright spots) Fringe seperation is constant.

Question 29

Whats the difference between a progressive and stationary wave?

Answer 29

Progressive waves transfers energy Stationary waves store energy

Question 30

Order of wavelengths of light.

Answer 30

R - Long wavelength O Y G B I V - Short wavelength

Question 31

What is propagation?

Answer 31

Movement of waves

Question 32

What is wave form?

Answer 32

Displacement-Time graphs for waves

Question 33

Difference between nodes and antinodes

Answer 33

Node = 0 displacement / amplitude Antinode = maximum displacement / amplitude Node & Antinode are 1/4 wavelengths apart

Question 34

How are stationary waves formed?

Answer 34

By superposition of 2 progressive waves in opposite directions. - No net transfer of energy - Same frequency

Question 35

What is the fundamental frequency?

Answer 35

Lowest possible frequency where a system can vibrate to create a stationary wave.

Question 36

What is a harmonic?

Answer 36

An integer multiple of the fundamental frequency.

Question 37

Closed end vs open end

Answer 37

Closed end = node Open end = antinode

Question 38

What are the first 4 harmonics in terms of wavelengths?

Answer 38

1st = 1/4 wavelengths 2nd = 1/2 wavelengths 3rd = 3/4 wavelengths 4th = 1 wavelength

Question 39

Progressive wave vs standing wave

Answer 39

Progressive - Energy transferred along it (flicking a string up and down) Standing ] - Points of max & min energy (nodes & antinodes)