waves

wave hello to 100% in this topic

waves

is a vibration or oscillation that travels through space and transfers energy

what does wave motion do?

transfers energy from one point to another but it does not transfer matter

types of waves

mechanical waves and electromagnetic waves

mechanical waves

they require a medium such as air or water to travel through

electromagnetic waves (medium)

does not require a medium through which to travel

two types mechanical waves

transverse and longitudinal

transverse waves

particles of the medium move perpendicular to the direction of wave travel (water waves)

longitudinal waves

particles of the medium more in a direction parallel to the direction of wave travel (sound)

Crest (peak)

the highest point of a wave

trough

the lowest point of a wave

equilibrium point

the vertical midpoint of a wave

wavelength (lamda)

the distance between two crests or troughs

amplitude (m)

the maximum displacement of a wave peak or trough from equilibrium

frequency (f)

the number of waves which pass a fixed point in one second (Hz)

period (T)

the time a wave takes to complete a wavelength (s)

reflection angle of incidence

angle of incidence = angle of reflection

where is the normal drawn?

perpendicular to the barrier

what happens to the wavelength in reflection?

wavelength stays the same

is this concave or convex?

concave

what is an echo?

is a reflection of sound

refraction def

is the bending of a wave when it enters a medium with a different wave speed

fst wd (also frequency)

fast to slow towards the normal, wavelength decreases, frequency stays the same

sfa wi

slow to the fast away from the normal, wavelength increase, frequency the same

total internal reflection

• when a wave goes from a slow to fast medium it bends away from the normal

• when the incident angle exceeds the critical angle tir occurs

• wave reflects back into the boundary

Diffraction def

is the bending of waves around small obstacles and the spreading out of waves beyond small openings

what leads to greater diffraction??

greater wavelength (most often answer)
wavelength and gap having the same magnitude

in diffraction wavelength and frequency is

the same as before

high frequency means what to the pitch

higher

what type of medium is sound the fastest in??

in solids, as they have strong atomic bonds and strong interactions between particles.

this means there is more collision between sound particles leading for sound to travel faster

what happens to the speed of sound when temp increases?

• the speed of sound in air increases when the temperature of the air increases.

• at higher temperatures particles have higher average speed and average kinetic energy.

• more energetic particles transfer energy more rapidly via collisions. temperature effects outweigh density effects within a given phase

when graphing from displacement to pressure the…

the crests and troughs become zero, and the zeros becomes compression or rarefaction

What are seismic waves?

Mechanical waves caused by events such as earthquakes.

What type of wave is a P wave?

A longitudinal compression wave.

What type of wave is an S wave?

A transverse (shear) wave.

Which seismic waves arrive first at a seismograph?

P waves.

Which seismic waves are generally more destructive?

S waves.

What does the velocity of a P wave depend on?

The material through which it travels.

How does P-wave velocity generally change with depth?

It increases with depth.

What happens to seismic waves when they encounter materials of different densities?

They refract.

State 2 ways seismic waves provide evidence about the Earth’s structure

 S-waves cannot travel through liquids, showing that the Earth's outer core is liquid.

Seismic waves refract and change speed as they pass through Earth, indicating the presence of layers with different densities and materials.

Explain how a mechanical wave transfers energy without transferring matter overall.

A mechanical wave transfers energy by causing particles in a medium to vibrate and pass energy to neighbouring particles.

The particles only oscillate around their equilibrium positions, so there Is no overall transfer of matter, only energy.

Superposition

The resultant displacement when two waves meet at a point

In Phase

When peaks and troughs align

Out of Phase

their peaks and troughs no longer align

Completely Out of Phase

Peak of one wave aligns with the trough of the other wave

Constructive Interference

occurs when 2 waves combine to give a larger wave

happens at max when 2 waves are IN PHASE

Destructive Interference

when two waves combine to give a smaller wave

happens at max when 2 waves are COMPLETELY OUT OF PHASE

How is the Angle of Incidence measured?

from the normal to the ray

Free Vibration

any object made of elastic material when disturbed will vibrate at a particular set of frequencies

dependent on the elasticity and shape of the object

Forced Oscillation

produced when an external periodic driving force vibrates a system

the system will vibrate at the same frequency as the applied force and will continue to vibrate as long as the force is applied

Resonance

occurs for a driven object if the force you are applying has same frequency as the natural frequency of the object

what happens at resonance?

the maximum amount of energy is being transferred to the object

you get the greatest response (amplitude) for least amount of input

Explain how resonance is achieved when a person is pushed on a swing

Frequency of the person pushing the swing matches the natural frequency of the swing

Resonance results in an ever increasing amplitude for the person being swung

Standing Waves

is a wave that does not appear to be progressing forwards

forms when 2 waves of the same amplitude and frequency, and travelling in opposite directions ae superimposed along a 1D line

Displacement Nodes

points on standing waves where destructive interference always occurs

lamda/2 apart

no displacement

Displacement Antinodes

the particles move up and down, or forwards and backwards (sound) and reach the maximum displacement possible (constructive inteference)

lamda/2 apart

Pressure Nodes

are points where the pressure in a standing sound wave is always at atmospheric pressure

sound cannot be heard as there is no pressure variation

occurs at displacement antinodes

Pressure Antinodes

the sound pressure varies constantly and reaches the maximum pressure possible

sound is most audible at these points

occur at displacement nodes

Explain how standing waves are produced

When 2 waves of the same speed, frequency and amplitude travelling in opposite directions along a 1D line are superposed

They occur as a result as resonance

Effects of standing wave

The wave profile does not move along the medium as energy doesn’t pass along it

Fluctuations occur between the nodes

Explain how reflected waves produce standing waves

The reflected wave has the same frequency, wavelength and speed and adds to the incident wave along 1D.

Therefore the conditions for the production of a standing wave are satisfied.

The first natural frequency is the

first harmonic

Opened ended pipe

A = N + 1

Close Ended Pipe (nodes and antinodes)

N = A

String

N = A + 1

Natural frequency

frequency that standing waves are established

almost all natural systems have more than one natural frequency

Beats

Beats occur when two sound waves of slightly different frequencies intefere with each other

How are beats produced?

When 2 sounds waves with close but not identical frequencies overlap, they interfere constructively and destructively with each other. The alternating pattern creates a beat frequency

If a classroom door is open slightly, you can hear a 200 Hz sound coming from the corridor yet you cannot see a 400 THZ beam of light in the corridor. Explain this observation

Sound has a much greater wavelength than light and therefore diffracts more when passing through the door

can show with calc where use the values from the formula sheet

Explain why when lightning occurs close to you it is heard as a high frequency crack, whereas when it is far away from you it is heard as a low frequency rumble

Low frequency sounds have longer wavelengths (lower pitch, lower frequency)

Therefore the sound of lightning diffracts around objects more easily and is therefore heard at greater distances from the source