Chapter 11 Waves 1

Question 1

Progressive Wave

Answer 1

Transfer energy from one place to another without transferring matter

Question 2

Transverse Wave

Answer 2

Oscillations perpendicular to direction of energy transfer

Question 3

Longitudinal Waves

Answer 3

Oscillations parallel to the direction of energy transfer

Question 4

Why is sound faster through a medium with higher density?

Answer 4

• Air particles are displaced by wave from EP according to force provided by neighbouring particles

In higher density medium:

• As medium’s particles are closer together
• Stronger restoring force
• Energy and vibrations passed more rapidly from one particle to another

Question 5

Displacement:

Answer 5

Distance from EP in a particular direction

Question 6

Amplitude

Answer 6

Max displacement of oscillating particle from EP

Question 7

Wavelength

Answer 7

Minimum distance between 2 points in phase on adjacent waves

Question 8

Period of oscillation

Answer 8

Time taken for one oscillation

Question 9

Frequency

Answer 9

Number of waves that pass a given point per unit time

Question 10

Wave Equation:

Answer 10

V = λf

Question 11

Frequency Equation

Answer 11

f = 1 / T

Question 12

Phase difference equation:

Answer 12

ϕ = (x / λ) * 2Π

Question 13

How can oscilloscope be used to determine wave frequency?

Answer 13

1. Using microscope, produce a trace on screen of oscilloscope
   - Each horizontal square reps a time interval AKA the timebase

Question 14

Settings of oscilloscope

Answer 14

• If timebase is 1.0 ms cm^-1, then each square reps a time interval of 1 ms
• A setting of 10 V cm^-1 reps a pd of 10V

Question 15

Reflection

Answer 15

When a wave changes direction at boundary between 2 different media remaining in original medium

Question 16

Law of reflection

Answer 16

Angle of incidence = Angle of reflection

Question 17

What changes happen to a wave when it undergoes reflection?

Answer 17

reFLection

- Frequency and Wavelength DO NOT change

Question 18

Refraction

Answer 18

When a wave changes direction as it changes speed when it passes from one medium to another
- There is always some partial reflection

Question 19

What are the rules for waves changing speed?

Answer 19

FAST PEOPLE ARE NOT NORMAL

• If wave slows, then it will refract towards the normal
• If wave quickens, it refracts away from the normal

Question 20

What are the rules for mediums in relation to the speed of EM and mechanical waves?

Answer 20

EM waves travel slower in more optically dense solutions

Mechanical waves tend to speed up as they enter a physically denser medium

The medium is often the opposite for either

Question 21

What changes happen to a wave when it undergoes refraction?

Answer 21

reFraction

• Refractions affects wavelengths
• Frequency is constant

Question 22

Do water waves travel faster in shallower or deeper water?

Answer 22

Think of TSUNAMIs

• Water wave slows down in shallower water
• Wavelength gets shorter

Question 23

Diffraction:

Answer 23

• Wave phenomena where when waves pass through a gap or travel around an obstacle, they spread out
• All waves can be diffracted

Question 24

Gap Size in diffraction:

Answer 24

• If wavelength and gap size are similar, it means there is greater diffraction

Question 25

What changes happen to a wave when it undergoes diffraction?

Answer 25

Nothing changes

Question 26

Polarisation:

Answer 26

Particles only oscillation along one direction MEANING that the wave is confined to a single plane of oscillation

Question 27

Why can't longitudinal waves be polarised?

Answer 27

Longitudinal waves have oscillations that are always parallel to direction of energy transfer so wave cannot be plane polarised as oscillations are already limited to only one place

Question 28

Partial Polarisation

Answer 28

- When transverse waves reflect off a surface, they become partially polarised - More waves oscillating in one particular place but wave is not completely plane polarised

Question 29

Intensity

Answer 29

Is defined as the radiant power passing through a surface per unit area

Question 30

Intensity equation

Answer 30

I = P / A For a point source: I = P / 4Πr^2

Question 31

Relationship between Intensity and Amplitude

Answer 31

Intensity ∝ Amplitude^2

Question 32

Explain relationship between Intensity and Amplitude:

Answer 32

- Decreased amplitude means reduced average speed of oscillating particles - Halving amplitude results in particles oscillating with half the speed, and a quarter of kinetic cheeks - Hence, intensity is directly proportional to the square of an amplitude

Question 33

EM Waves:

Answer 33

Electric and Magnetic fields oscillating at right angles to each other

Question 34

Visible Light range:

Answer 34

700nm - 400nm

Question 35

What is used to polarise microwaves?

Answer 35

A metal grille is used

Question 36

Refractive Index Equation:

Answer 36

n = c / v - n is refractive index

Question 37

Refraction Law:

Answer 37

n sin θ = k | n1 sin θ1 = n2 sin θ2

Question 38

2 conditions for Total Internal Reflection:

Answer 38

1. Light must be travelling from high refractive index to low refractive index 2. Incidence Angle > Critical Angle

Question 39

What happens to light at Critical Angle?

Answer 39

Light refracts along the boundary between 2 media | 90 degrees

Question 40

For air, what is refractive index equation:

Answer 40

sin C = 1 / n