Waves

Question 1

What are waves ?

Answer 1

The transmission of energy without the transmission of matter or movement of energy from one place to another without moving a medium from one place to another .

Question 2

How do mechanical waves work?

Answer 2

They move through the particles in a medium by either moving them backwards and forwards( longitudinal) or side to side (transverse)

Question 3

After a wave passes, where do the particles go?

Answer 3

The particles return to its original place but the energy is transferred to the wave’s destination.

Question 4

Longitudinal Waves

Answer 4

The particles are oscillated in a back and forth motion that is parallel to the motion that the energy travels.
Examples
- Sound waves
- P waves from earthquakes
-tuning fork ( compression and rarefactions in the air particles)

Question 5

How longitudinal waves transfers?

Answer 5

By compressions and rarefactions

Question 6

Compressions

Answer 6

The regions where the particles are pushed closest together.
Wavelength: from one compression to the next successive one

Question 7

Rarefactions

Answer 7

Regions where the particles are pulled apart.

Wavelength: from one rarefaction to the next successive one

Question 8

Transverse waves

Answer 8

Particles move at right angles (side to side or up or down) to the direction that the wave travels ( perpendicular to the wave direction). The particles return to equilibrium after the wave passed. However, they do not require a medium to travel.
- the majority of waves
Example: Electromagnetic waves

Question 9

Electromagnetic Waves

Answer 9

They are transverse waves and need no medium to travel through.

Question 10

Speed of light

Answer 10

c=3.00x10^8

Question 11

Electromagnetic waves

Answer 11

Increase in frequency

Radio & microwaves –> Infrared –> visible light(ROYGBIV) –> Ultraviolet –> X-rays –> Gamma Rays

Question 12

Amplitude

Answer 12

Measured from the peak or maximum displacement to the equilibrium point ( how much energy a wave has)

Question 13

Wavelength , λ

Answer 13

Distance traveled in a complete oscillation or the distance between two successive troughs or crests.

Question 14

Frequency

Answer 14

The number of cycles in one second and is measured in hertz, Hz.
f= cycles/ seconds

Question 15

Period, T

Answer 15

Time taken to complete one cycle

T= 1/f

Question 16

Velocity of a wave

Answer 16

v= Frequency x wavelength 
v = fλ

Question 17

Velocity at maximum displacement/ extremes

Answer 17

Equal to zero

Question 18

Speed of a wave of a string

Answer 18

This is dependent on the properties of the medium through which the wave travels

Question 19

Velocity of a wave of a string

Answer 19

The velocity that the wave moves with to the specific direction is dependent on the acceleration at which each consecutive particle moves with. ( upwards or side to side) due to the net pulling that each particle has on the next.

Question 20

Speed of a wave of a string formula deriving

Answer 20

From newton’s 2nd Law
- As F increases, acc increases and Velocity increase
- for one particle to exert a force on the other, tension needed
as tension increases, velocity increases
-smaller mass, velocity increases
mass per unit length/ linear density
m/L
Therefore v=√F applied / m/L
Force applied= tension
m/L = μ
Therefore v=√ T/μ

Question 21

1st Law of Reflection

Answer 21

Angle of incidence = angle of reflection

- Measured from a normal perpendicular to the surface at point of incidence.

Question 22

2nd Law of reflection

Answer 22

Incident ray, reflected ray and normal all lie in the same plane

Question 23

Types of reflection ( determined by smoothness)

Answer 23

Regular reflection
for very smooth surfaces (mirrors) all incident rays are reflected parallel to each other
Diffused reflection
on rough surfaces, the rays are reflected at many different angles

Question 24

Reflection of waves

Answer 24

All waves can be reflected

At any point where there is a change in wave velocity or where the wave meets upon a boundary and is reflected

Question 25

Reflection of waves ( Phase)

Answer 25

When reflected, waves are out of phase or opposite to the original wave.

Question 26

Reflection (phase change)

Answer 26

At a fixed end, there is a change of phase but at a free end there is no phase change

Question 27

A change in medium brings about a ……?

Answer 27

Change in speed of wave and some energy of incident wave is reflected(phase change, v1=constant) and some is transmitted(no phase change,v2

Question 28

Ray

Answer 28

Arrow drawn on diagram to show direction of propagation of a set of waves and is at 90 degrees to the wavelength.

Question 29

Huygen’s Principle

Answer 29

When predicting the future position of a wavelength ,each point on the wave is considered a source of waves, called “secondary wavelets”

Question 30

Application of Huygen’s Principle

Answer 30

1. Choose a point on the wavefront
2. Draw an arc to the point chosen and call the radius ‘vt’, distance moved in a particular time
3. Choose another point and repeat first steps
4. Draw a tangent to the two arc and this is the new wavefront

Question 31

Refraction has:

Answer 31

• change in direction of wave
• When waves move across a boundary between two different mediums with change in speed
• Change in speed results in change in the propagation of a wave.`

Question 32

Huygen’s Principle predictions

Answer 32

Huygen’s principles predicts where a wavefront will appear due to the difference in speed when a wave passes through a different medium.
- using the wavelets principle, each wavelet meets the boundary at different times and passes through the medium with distance ‘vt ‘

Question 33

Huygen’s Principle predictions part 2

Answer 33

Since each wavelet of a wavefront moves a specific distance across the boundary at different distances in the same time, then this translates into a change in wavelength.

Question 34

Mathematical Application of Huygen

Answer 34

When a wave front and its refraction are taken into consideration, it makes a quadrilateral with corners = 90 degrees.
- Therefore
sin∅i÷sin∅r=vi ÷vr

Question 35

Snell’s Law

Answer 35

n= index of refraction
i= angle of incidence
r= angle of refraction
* Only applies to rays travelling from air into another medium