WAVES

What are x-rays used for?

medical imaging allows us to view the internal structure of things

how do X-rays work in medical imaging?

1. fires X-rays at a person's body and recording the ones that get through using a detector plate

2. works as X-rays are absorbed by dense materials such as bone, but will be able to pass through the parts that are mostly air like our lungs and intestines, they'll only partially pass through fleshy parts eg. heart

3. the images start off completely white and go black if that area if the detector plate receives radiation, so it's only our bones that appear white and everything else is black or a shade of grey

Why are gamma rays dangerous and why do we still use them

ionising radiation which can damage our cells and lead to cancer, however it also helps us to diagnose + treat diseases so it's worth the risk

what are the three uses of gamma rays

sterilisation ( medicine) - boiling water can be used but it may damage the tool if it's plastic ( they melt) but gamma rays don't do any damage at all

used in medical imaging/treating cancer using radiotherapy

sterilisation ( food) - can kill microorganisms without causing any other damage

What is ultrasound?

sound waves that vibrate at frequencies above 20,000 Hz so above the range of human hearing

how do ultrasound waves work using partial reflection?

when ultrasound hits a boundary between two mediums some is reflected then some will be transmitted through and refracted = partial reflection

how do ultrasounds tell us about the internal structure of an object?

1. we know that when we fire ultrasound waves at an object that the waves will travel through the object, but everytime it hits a boundary some of the waves are reflected back to us

2. so if we know the speed of the wave and the time it takes to be reflected we know how far away that boundary is which tells us about its internal structure

how are ultrasounds used in fetal imaging?

1. place an ultrasound device ( which is connected to an ultrasound machine) and place it on a pregnant woman's belly. This device can transmit and receive information

2. the ultrasound waves are fired at the belly and everytime it passes from one medium to another (eg. between tissue and the fluid surrounding the foetus) some of the waves are reflected back to the device

3. the timings and distributions of these echoes are produced by a computer to produce a live image of the foetus

how are ultrasounds used to check the quality of products in industry?

1. if we fire ultrasound waves at the object, as the material is completely solid the wave should pass straight through and only be partially reflected at the beginning and the end of the object because this is where mediums are changing

2. if there's a crack then the waves are partially reflected from the crack and so the company can tell that there's a fault as we're getting reflected waves we didn't expect

what is reflection

The bouncing of light off a surface

What is the angle of incidence?

The angle between the incoming wave and the normal

What is the angle of reflection?

The angle between the reflected wave and the normal

what is the normal line

An imaginary line that's perpendicular to the surface at the point where the wave hits the surface

what is total internal reflection (TIR)?

complete reflection of a ray of light within a medium, this occurs when the angle of incidence is too big, the critical angle is the minimum angle at which TIR will occur

specular reflection

a reflection produced by a smooth surface in which parallel light rays are reflected in parallel eg. in a mirror, so the normal lines are in the same direction

diffuse reflection

Reflection that occurs when parallel rays of light hit a rough surface and all reflect at different angles

What is refraction?

when waves change direction as they pass from one medium to another

what happens when the light ray enters a denser medium in refraction

slows down and it bends towards the normal

what happens when a light ray enters a less dense medium in refraction

speeds up and bends away from the normal

what is the emergent ray

the ray of light that emerges from a medium

when are seismic waves released

whenever large scale events like volcanoes and earthquakes occur, seismic waves are released from the earthquake's focus in all directions and so can be detected all around the world

what are P- waves

they are longitudinal , can travel through both solids & liquids, moves by a pushing/pulsing motion and much faster than S-waves arrives ''first''

what are S- waves

they are transverse, ONLY travels through solids, moves by a shearing motion (up & down) and causes the most damage, arrives "second"

how are seismologists able to learn about the internal structure of the earth

by tracking the paths of both types of seismic waves as S-waves can only pass through the solid path of the earth whereas P-waves can pass through both the solid and liquid parts

shadow zones

Areas on Earth's surface where no seismic waves are recorded, shadow zones are created by the outer core as these are regions where S-waves can't reach

how can seismologists determine the epicentre of an earthquake

by measuring the time delays between the waves being detected in each location

P-waves and the earth's internal structure

P-waves can pass through each layer, refracting at each boundary, and can be detected all around the earth

S-waves and the earth's internal structure

S-waves cannot pass through the liquid outer core, so they are reflected back through the mantle towards the surface

what happens when waves reach a boundary between two different mediums

they are either, reflected, absorbed or transmitted

waves transfer _______ from one place to another

energy

What is the time period of a wave?

The time taken for one complete oscillation

Equation for frequency

f = 1/T

T = time period

equation for wave speed

wave speed = frequency x wavelength

What is the amplitude of a wave?

the distance between the middle and crest or trough of a wave

What is the crest of a wave?

the highest part of a wave

What is the trough of a wave?

the lowest part of a wave

what is the displacement of a wave?

How far a point on the wave has moved from its undisturbed position( from the x-axis middle line)

what is one entire oscillation of a wave

from one crest to another

transverse wave

oscillations are perpendicular to the direction of energy transfer

examples of transverse waves

electromagnetic

radio waves

ripples/waves

longitudinal wave

Oscillations are parallel to the direction of energy transfer

Examples of longitudinal waves

Sound, Seismic P-waves

are E-m waves longitudinal or transverse?

they're all transverse

what speed do E-m waves travel at

they all travel at the same speed of 3x10^8 m/s

E-m waves are in order of increasing _______ and decreasing _________

frequency, wavelength

which of the E-m waves are ionising

UV, X-rays and gamma rays

acronym to remember the colours of visible light

ROYGBIV

all lenses have a principle focus on _____ sides

both

convex lens/converging lens

A lens that is thickest in the middle, causing parallel rays of light to converge (come together) to a focus ( called the focal point). The focal length of a converging lens is positive

concave lens (diverging lens)

A lens that is thinner in the middle and gets wider at the ends , causing parallel rays of light to diverge (spread out) from a focus on the same side of the lens that the object is. The focal length of a diverging lens is negative.

how to determine if an image is real

the image is inverted

what makes a lense strong

if it has a short focal length, if it is more curved and depending on the material

what is a real image

When the light rays from the object actually do come together to form an image, which can be captured on a screen

explain an example of a real image

light rays from a spanner pass through the lens in our eye and form a real image on our retina however it is inverted but our brain just converts it so that it's upright

What is a virtual image?

formed when the diverging light rays don't come together where the image appears to be

explain an example of a virtual image

eg. in a mirror the image appears to be behind the mirror however there can't actually be any ray behind the mirror as it's a solid object that light can't pass through so it's only a virtual image formed from virtual rays

how to draw a ray diagram of a concave lens

1. pick a point near to the top of the object and draw a horizontal line running through the lens that is parallel to the axis and one diagonal line running through the centre of the lens

2. the first ray is refracted however not the second one that runs through the centre of the lens

3. to find the position of the image draw a dotted line from the point where the refracted ray hits the lens, back to the focal point

4. the point where the rays cross is the top of our image

how to draw a ray diagram for a convex lens

1. same initial process as concave lens ( draw one horizontal line and one running through the centre of the lens)

2. the light ray will be refracted so that it passes through the focal point on the other side of the lens and carries on going

3. find the point where the light rays cross and this is the top of your image

what size will the image be if the object is more than 2x the focal length?

smaller

what size will the image be if the object is exactly 2x the focal length?

the same size as the object

what size will the image be if the object is in between F and 2F?

image will be larger than the object

what happens to the image if the object is between the focal point and the lens itsef

the refracted rays won't ever meet, so to find our image we must trace it back using virtual rays

what images do convex lenses form

real and virtual images

how do we generate radiowaves?

1. use a transmiter connected to an oscilloscope to see the frequency of the AC we're using because the oscilloscope allows us to see this on the screen ( which is important because the frequency of the AC determines the type of wave we're going to produce)

2. we then detect the radiowave using a receiver which absorbs the energy and generates another AC which it displays on another oscilloscope

3. the frequency of this AC current it produces is the same as the frequency we used to generate the radiowave in the first place

what is the main use for radiowaves

communication

what are the three types of radiowaves

long waves, short waves and very short waves

what are long waves used for

long waves can be transmitted long distances ( eg. UK to Singapore) without having to interact with anything along the way. This is because they can diffract (bend) around the curved surface of the earth

what are short waves used for

short waves can also be transmitted long distances however they can't curve around the earth. So instead they're reflected from the ionosphere (electrically charged layer of the upper atmosphere) so they're mainly used for things such as bluetooth

what are very short waves used for

TV and FM radios ; these ones have to travel directly from the transmitter to your receiver, which is why you don't always get a great radio signal in the car because surrounding structures like tunnels can get in the way

what are the two types of microwaves

1. microwaves that aren't absorbed by water molecules

2. microwaves that are absorbed by water molecules

how and why are microwaves that aren't absorbed by water molecules used in communications

used for communication using satelites as they have to pass through the earth's atmosphere which contains a lot of water vapour

how it works is that once the microwaves make it through they are received by a satlelite then transmitted back down to earth where we can detect them using a satelite dish

how are microwaves that are absorbed by water molecules used in heating our food in microwave ovens

most of the food we eat contains lots of water molecules, when microwaves are fired at our food, the energy from the waves gets absorbed by all the water molecules and as the water molecules vibrate more due to all the new energy, they transfer energy to neighbouring particles and so it spreads through the food via conduction and convection

what are the dangers of microwaves

if exposed to it for too long it can cause heating of body tissues

what are the dangers of infrared radiation

can be absorbed into the skin and cause skin burns

infrared radiation is emitted from all objects that have ________ energy

thermal

What are the uses of infrared radiation?

electrical heaters, cooking food, infrared cameras

how is IR used in cooking?

heating metals eg. ovens and grills to very high temperatures emits lots of IR so it heats our food by transferring the heat energy ( however it doesn't penetrate the surface of the food unlike microwaves)

how is IR used in electric heaters?

uses electrical energy to heat the metal; because it's so hot the heater emits IR to the surroundings

what has the longest wavelength in visible light?

red

what has the shortest wavelength in visible light

violet

How are real images formed?

By the convergence of actual light rays

a convex mirror forms a _______ image behind the mirror

virtual

a concave mirror can form a ____ image if the object is _______ ______ than the focal point

real , further away

how is visible light used in communication

using optical fibres - they are thin glass or plastic fibres that are able to transmit pulses of light over long distances because light is reflected every time it hits the surface and so it ends up bouncing back and forth until it emerges at the other end of the fibre where it can be interpreted

It uses : total internal reflection and it's specular reflection

UV light is emitted from the _____

sun

what are the use of UV radiation

- security eg. security pens

- fluorescent lights : generate UV radiation, aborbed by a layer of phosphorus then re emits the energy as visible light

- tanning beds

- sterilising water

what are sound waves and how do they travel

they are vibrations that pass through the molecules of a medium, as they are longitudinal waves they travel through a series of compressions and rarefactions

what are reflections of sound waves called

echoes

why can't sound waves travel in space?

because space is a vacuum so there are no particles to vibrate for the sound to be transferred/pass through

How do sound waves travel through a solid?

when sound waves travel through a solid they cause the particles in the solid to vibrate, these particles then gain kinetic energy and collide into neighbouring particles, transferring kinetic energy through the solid over and over again as the sound wave gets transmitted through the material

Why do sound waves travel faster through solids / denser materials?

The particles in a solid are closer together/ densely packed than in a gas or a liquid.

This means vibrations are more easily passed from particle to particle and so sound travels faster.

how are sound waves transmitted

1. sound waves enter the ear and travel down the ear canal and hit the ear drum

2. this cause the eardrum to vibrate, causing the vibrations to be transmitted down the ossicles( tiny bones in the ear)

3. then goes along the semi circular canal and into the cochlea

4. the cochlea then converts the vibrations into electrical signals and these electrical signals get sent along the auditory nerve to your brain

What is the range of human hearing?

20-20,000 Hz

what happens to our hearing as we age?

the older we get the range of our hearing decreases due to wear and tear of the cochlea

what is the acronym to remember the colours of visible light

R- red

O- orange

Y - yellow

G- green

B - blue

I - indigo

V - violet

violet has the ______ wavelength and ________ frequency

shortest wavelength and highest frequency

red has the _______ wavelength and ________ frequency

longest wavelength and lowest frequency

why isn't black on the spectrum

because it it just the absence of light

why isn't white on the spectrum

because it's a combination of all the colours/wavelengths of the spectrum

What are opaque objects?

Objects that do not transmit light. When visible light waves hit them, they absorb some wavelengths of light and reflect others (eg. yellow cheese reflects either yellow or a combination of red and green so that is why it appears yellow)