Topic 6 - waves

wavelength

distance between the same points on 2 consecutive waves

amplitude

distance from the equilibrium line to the maximum displacmnet

freuqnecy

the number of waves that pass a single point per second

period

the time taken for a whole wave to completely pass a single point

velocity =

frequency x wavelength

period =

1 / frequency

relationships (p and f)

• period is inversely proportional to frequency

• smaller period = higher frequency = greater velocity

what are the 2 types of waves?

transverse and longitudinal

transverse waves

• vibrate perpendicular to the direction of travel

• have peaks and troughs

• e.i light or waves on the electromagnetic spectrum

longitudinal waves

• vibrate parallel to the direction of travel

• have compressions and rarefactions

• e.g. sound waves

RP -- measuring velocity in a ripple tank

• place a pencil at any point on the tank.

• Then you time for a minute and you count how many waves pass the point in a minute, then divide by 60 to get the number of waves per second.

reflections of waves

• light will reflect if the object is opaque and is not absorbed by the material because the electrons will absorb the light energy and then re emit is as a reflected wave

• the smoother the surface the stronger the reflected wave

• roughs surfaces scatter the light in all directions

• angle of incidence = angle of reflection

transmissions

• the process of passing through the material and emerging

• occur when waves pass through a transparent material

absorption

• if the frequency of light matches the energy levels of the electrons the light will be absorbed

• if a material appears green, only green light has been reflected and the rest of the frequencies in visible light have been absorbed

sound waves:

• sound waves travel through solids causing vibrations

• our outer ear collects the sound and channels it down the earl canal

• the sound wave hits the eardrum (a tightly stretched membrane which vibrate as the pressure air waves reach it)

• the eardrum vibrates at the same frequency of the sound wave, converting the sound energy into mechanical vibrations, which are then transmitted to the inner ear for processing.

compression and rarefaction on eardrum

• Compression forces the eardrum inward

• Rarefaction forces the eardrum outward, due to pressure

what range can humans hear

20Hz to 20 000Hz as it gives us the greatest survival advantages

what happens when we listen to loud sounds

• in the cochlea the hair can die or get damaged

• so we cant listen to higher frequency sounds

what happens to ultrasound when it reaches a boundary between 2 medias

• they are partially reflected back

  • the rest pass through

a receiver next to the emitter can record the reflected waves:

• the speed of the waves are constant, so measuring the time between emission and detection can show distance from the source

what are the 2 sesmic waves

• primary waves

• secondary waves

P waves

• longtidunal

• can pass through solids and liquids

• faster

S waves

• transverse

• only pass through solids

how do we know the earths centre is liquid

on the other side of the earth only P waves are detected because S waves cant penetrate liquid

how to find the depth in the ocean

• a pulse of ultrasound can be sent below the ship, time taken to reflect can be used to calculate depth

• used to find how far the seabed is below the ship

are EM waves logitudinal or transvers

• transverse

trend from radio wave to gamma ray

• decreasing wavlength causes increasing frequency

• as frequency increases, energy of the wave increases

The EM spectrum

• radio

• microwave

• infrared

• visible

• ultraviolet

• X-ray

• Gamma ray

in space all waves …

• have the same velocity

if entering a denser material the light will …

bend towards the normal because it slows down

• (shorter wavelengths slow down more than longer wavelengths, blue light shows more than read)

why do materials interact differently with different parts of the EM spectrum

because the wavelengths and frequency are different

what has a longer wavelength red or blue

red

Why does dispersion of white light happen in a prism?

• The different wavelengths refract a different amount,

• depending on their wavelength

• red refracts the least

how are radio wave produced

• oscillation in electrical circuits

• when radio waves are absorbed they create an alternating current the same frequency as the radio waves

when electrons move to a higher orbit …

the atoms has absorbed EM radiation

when the electrons falls to a lower orbit

the atoms has emitted EM radiation

if an electron gains enough energy …

It can leave the atom to form an ion

where are gamma rays originate from?

the decay of an atomic nuclei

what rays are hazardous for human

• UV light

• x rays

• gamma rays

what is radiation dose

how much exposure leads to harm for a person

X-ray risks

• ionisation radiation that can cause the mutation of genes - causing cancer

Uses of EM waves

• Radio - TV and radio

  • Long wavelength, can travel far without losing quality

• Microwaves - Satellite communication, cooking food

  • Can penetrate atmosphere to reach satellites

• Infrared - Cooking food, infrared cameras

  • Transfers thermal energy

• Visible - Fibre optics

  • Best reflection/scattering in glass (others have too short/long wavelengths)

• UV - Sun tanning, energy efficient lamps

  • Radiates the least heat but more energy

• X-ray - Medical imaging and treatment (and gamma)

  • Very high in energy, and can penetrate material easily

convex lenses (virtual or real)

both

concave virtual or real

only virtual image

concave lens

• spreads light outwards

• used in glasses to correct short sightedness

convex lenses

• focus light inwards

• used for magnifications

• used to correct long - sightedness as it focuses the rays closer

magnification =

image height/ object height

specular is

a single reflection of a smooth surface

diffuse

reflections off a rough surface causes scattering

how do colour filters work

they only let one wavelength (colour) through and absorb every other colour

if all wavelengths are reflected its

white!

id all wavelengths are absorbed its

black

the wavelength which is absorbed =

the colour it appears

do all objects emit and absorb infrared radiation

yes

the hotter the body:

• the greater amount of radiation released per second

• the greater amount of short wavelength radiation releases

what is a black body

• an object that absorbs all the radiation it recieves,

• it emits all radiation

if a body is increasing tempreature

it is absorbing more energy that it emitts

if a body is cooling down

energy is released at a greater rate than it absorbs

green house gas effect

YAYAYAYAY

similarty of tranverse and longitutidinal

both transfer energy without transfering matter