Waves Flashcards

1
Q

What are waves ?

A

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 .

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2
Q

How do mechanical waves work?

A

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

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3
Q

After a wave passes, where do the particles go?

A

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

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4
Q

Longitudinal Waves

A

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)

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5
Q

How longitudinal waves transfers?

A

By compressions and rarefactions

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6
Q

Compressions

A

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

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7
Q

Rarefactions

A

Regions where the particles are pulled apart.

Wavelength: from one rarefaction to the next successive one

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8
Q

Transverse waves

A

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

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9
Q

Electromagnetic Waves

A

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

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10
Q

Speed of light

A

c=3.00x10^8

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11
Q

Electromagnetic waves

A

Increase in frequency

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

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12
Q

Amplitude

A

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

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13
Q

Wavelength , λ

A

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

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14
Q

Frequency

A

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

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15
Q

Period, T

A

Time taken to complete one cycle

T= 1/f

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16
Q

Velocity of a wave

A
v= Frequency x wavelength 
v = fλ
17
Q

Velocity at maximum displacement/ extremes

A

Equal to zero

18
Q

Speed of a wave of a string

A

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

19
Q

Velocity of a wave of a string

A

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.

20
Q

Speed of a wave of a string formula deriving

A

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

21
Q

1st Law of Reflection

A

Angle of incidence = angle of reflection

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

22
Q

2nd Law of reflection

A

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

23
Q

Types of reflection ( determined by smoothness)

A

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

24
Q

Reflection of waves

A

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

25
Reflection of waves ( Phase)
When reflected, waves are out of phase or opposite to the original wave.
26
Reflection (phase change)
At a fixed end, there is a change of phase but at a free end there is no phase change
27
A change in medium brings about a ......?
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
28
Ray
Arrow drawn on diagram to show direction of propagation of a set of waves and is at 90 degrees to the wavelength.
29
Huygen's Principle
When predicting the future position of a wavelength ,each point on the wave is considered a source of waves, called "secondary wavelets"
30
Application of Huygen's Principle
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
31
Refraction has:
- 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.`
32
Huygen's Principle predictions
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 '
33
Huygen's Principle predictions part 2
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.
34
Mathematical Application of Huygen
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
35
Snell's Law
n= index of refraction i= angle of incidence r= angle of refraction * Only applies to rays travelling from air into another medium