waves

wavelength is the distance from one peak to the next

what is the wavelength?

frequency is how many complete waves there are per second measure in hertz Hz. 1Hz is 1 wave per second

what is the frequency?

amplitude is the height of the wave from rest to crest

what is amplitude?

the period T is the time it takes in s for one complete waves to pass a point

what is the period?

what is the formula for frequency?

what is the formula for wavespeed?

in transverse waves the vibrations are at 90 degrees to the direction energy is transferred by the wave.

e.gs:

* light and all other EM waves
* a slinky spring wiggled up and down
* waves on strings
* ripples on water

what is a transverse wave and e.gs?

in longitudinal waves the vibrations are along the same directions as the wave transfers energy

e.g’s?

* sound and ultrasound
* shock waves egg some seismic waves
* a slinky spring when you push the end

what is a longitudinal wave and e.g’s?

all waves carry and transfer energy in the direction they’re traveling.

e.g microwaves in an oven make things warm up - their energy is transferred to the food your cooking.

sound waves can make things vibrate or more e.g loud bangs can start avalanches.

what do all waves carry and transfer?

used as singles to transfer information from one place to another

e.g light in optical fibres or radio waves travelling through the air

what can waves also be used for?

they have wavefronts

* there are multiple waves moving together in the same direction
* the distance between each wavefront is = to one wavelength

what do 2 or more waves moving together have?

wavefronts are imaginary planes that cut across all waves connecting the point on adjacent waves which are vibrating together.

what is a wavefront?

the doppler effect makes waves longer or shorter

the waves produced by a source which is moving towards or away from an observer will have a different wavelength that they would if the source were stationary.

this is bc the wavespeed is constant . the wavefronts will bunch up in front of the moving source and spread out behind it.

what is the doppler effect?

will be higher and its wavelength will be shorter than the wave produced by the source

the frequency of a wave from a source moving towards you will be what?

it will be lower and it’s wavelength will be longer than the wave produced by the source.

the frequency of a wave from a source moving away from you will be what?

the longer its wavelength will be

the faster a wave is moving away from you the what?

red has the longest wavelength low freq

violet has the shortest wavelength high freq

what are the 7 types of electromagnetic waves?

they are all transverse waves and travel at the same speed through free space (vacuum)

all types of EM radiation is what type of wave?

radio waves are used mainly in communication:

radio waves are EM radiation with wavelength longer than about 10cm.

used for TV and FM radio broadcasting very short wavelength.

what are radio waves for?

long wave radio (wavelength 1-10km) can be transmitted a long wave because long wavelength are bent around the curved surface of the earth.

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what is long wave radio?

short wave radio wavelength (10-100m) can also be received at long distances from the transmitter. tis is bc they are reflected from the ionosphere ( a layer of the earth’s atmosphere).

what is short wave radio?

used for satellite communication and heating food

* wavelength 1-10cm

what are microwaves used for?

satellite communication (satellite TV signal and satellite phones) used microwaves

tv- signal from a transmitter is transmitted into space where it is picked up by the satellite receiver dish orbiting. satellite transmits signal back to earth received by satellite dish on ground.

mobile phone also travel as microwaves from your phone to nearest transmitter

what is satellite communication?

used for cooking

* microwaves are absorbed by the water molecules in the food.
* they penetrate a few centimetre in the food before being absorbed.
* energy is conducted or convected to the other parts of the food

what is the other use of microwaves?

used for heating and to monitor temp

* known as heat radiation.
* electrical heaters radiate IR to keep us war and grill use IR to cook food
* the hotter the object the more IR radiation gives out
* IR radiation given out by injects can be detected in the dark by nigh vision equipment
* electrical signal displayed on the screen as a picture which would be hidden in the dark e.g criminal on the run

what is infrared radiation?

can travel through optical fibres

* visible light can be used for communication using optical fibres

what are light signals?

optical fibres carry data over long distances as pulses of light

work by bouncing waves off the sides of a very narrow core

pulse of light enters the fibre at a certain angle at one end and is reflected again and again until it emerges at the other end

how do optical fibres work?

used for telephone and broadband internet cables.

used for medical purposes to see inside the body without having to operate

what are optical fibres used for?

* photography
* came uses a lens to focus visible light onto a light sensitive film or sensor
* the lens aperture controls how much light enters the camera
* the shutter speed determines how long the film or seniors is exposed to the light

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what is visible light used for?

used in fluorescent lamps

* fluorescence is a property of certain chemicals where ultraviolet radiation UV is absorbed and then visible light is emitted.
* they emit light
* fluorescent light use UV radiation to emit visible light. There safe to use as nearly all the UV radiation is absorbed by a phosphor coating on the inside of the glass which emits visible light instead
* fluorescent lights are more energy efficient than filament light bulbs

what is ultraviolet light used for?

* used to view the internal structure of object and materials bodies
* X-rays are directed through the body onto a detector plate.
* radiographers in hospitals take X-ray photographs to help doctors diagnose broken bone
* easily pass through flesh but not through denser material like bones
* can cause mutations which lead to cancer

what are x-rays used for?

1- sterilising medical equipment by killing all the microbes

2- food by killing microbes and keeping them fresh for longer

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what can gamma radiation be useful for?

some EM radiation enter living tissue

mostly passes through soft tissue without being absorbed

other type are absorbed and cause heating of the cell

some radiation can cause cancerous changes in living cell

how can EM radiation be harmful to people?

the more energy it has and the more harmful it is.

the higher the frequency of EM radiation the what?

internal heating- the heating of molecules inside things as in microwave ovens.

microwaves heat human body tissue

that is why they need to have shielding to prevent microwaves reaching the user

how is the body affected if it is exposed to too much of microwave radiation?

it can make the surface molecules of any substance vibrate- heating effect

higher frequency carries more energy than microwave radiation.

if too much infrared radiation skin burns

protect yourself using insulating materials to reduce the amount of IR reaching your skin

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how is the body affected if it is exposed to too much of infrared radiation?

damage surface cells and cause blindness.

some frequencies of UV radiation are ‘ionising’- carry enough energy to knock electrons off atoms.

can cause cell mutation or destruction and cancer.

wear sunscreen with uv filters when in sun

stay out of strong sunlight to protect skin from UV radiaiton

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how is the body affected if it is exposed to too much of UV radiation?

very high frequency waves such as gamma rays are also ionising and carry much more energy than UV rays.

much more damaging and can penetrate further into body.

cause cell mutation destruction leading to tissue damage or cancer.

how is the body affected if it is exposed to too much of gamma radiation?

when light bounces off an even surface

how does reflection happen?

when a wave slows down or speeds up at a boundary between 2 materials.

how does refraction happen?

lets us see thing light bounces off them into our eyes

how does reflection of light help us?

visible light is a transverse wave

what type of wave is visible light?

when light reflects from and uneven surface such as a piece of paper the light reflects off at all different angles

what is diffuse reflection?

when light reflects from an even surface smooth and shiny like a mirror then it is reflected at the same angle

what is clear reflection?

angle of incidence = angle of reflection

what is the law of reflection?

an imaginary lines that is perpendicular at right angles to the surface at the point of incidence where the wave hits the boundary.

shown as a dotted line

what is the normal?

angle between the incoming wave and the normal

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what is the angle of incidence?

the angle between the reflected wave and the normal.

what is the angle of reflection?

travel at different speeds in substance which have different densities.

EM waves travel more slowly in denser media

sound waves travel faster in denser substance

how do waves travel?

it speed

so when a wave crosses a boundary between 2 substances from glass to air what changes?

shows the path that a wave travels

what is a ray diagram?

* start by drawing the boundary between 2 materials and the normal (90 degrees to boundary)
* draw an incident ray that meets the normal at the boundary
* draw the refracted ray on the other side.
* if the second material is denser than the first the refracted ray will bends towards the normal.
* the angle between the refracted ray and the normal is smaller than the angle of incidence
* if the second material is less dense the angle of refraction is larger than the angle of incidence.

how to draw a ray diagram?

• shine a light ray at an angle into the block .

• some light will reflect but a lot passes through the glass and gets refracted

• trace the incident and emergent rays onto the piece of paper and remove the block

• draw in the refracted ray through the block by joining the ends of the other two rats with a straight line

• as the light passes from the air into the block it bends towards the normal as it slows down

• when the light reaches the boundary on the other side of the block it’s passing into a less dense medium. speeds up and bends away from normal

experiment with refraction using a light source and a rectangular block

different wavelength of light refract by different amount so the white light disperses into different colours as it enters a prism rainbow effect.

what happens when you shine white light into a triangular prism?

tells you how fast light travels in that material.

what does the refractive index of a transparent material tell you?

what is the formula for refractive index?

high

if light slows down a lot in glass is the refractive index low or high?

what is snell’s law?

using a glass block

* Draw around a rectangle glass block on a piece of paper and direct a ray of light though it at an angle
* trace the incident and emergent rays, remove the block then draw in the refracted ray between them.
* draw in the normal at 90 degrees to the edge of the block at the point where the rays enter the block
* use a protractor to measure the angle of incidence and the angle of refraction.
* calculate the refractive index using snell’s law?

how can you find the refractive index of glass?

* use a semicircular block.
* incident light ray is aimed at the curved edge of the block
* always enters at right angle to the edge
* doesn’t bends as it enter only bend when it leaves
* mark the positions of the rays and the blocks on paper use a protractor

what is an experiment to show total internal reflection?

what is the formula for finding critical angle?

optical fibres and prisms

2 uses of internal reflection?

made of plastic or glass consists of a central core surrounded by cladding with a lower refractive index

what are optical fibres made out of?