Science Y9 T1: Waves

energy

a property that allows physical work to be done

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a property a body has that helps it move against a work (kinetic and potential)

heat (thermal energy)

energy that comes from a substance whose molecules and atoms are vibrating faster due to a rise in temperature (a form of kinetic energy)

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the amount of vibration that particles have

insulator

a material that does not allow charge or heat to pass through it easily

conduction

the transfer of heat through solids

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heat is passed through vibration to neighbouring particles

convection

the transfer of heat through liquids and gasses

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heat decreases density → causes them to rise → particles cool down → heated once again

radiation

heat transfer in the form of infrared waves (no particles involved)

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electromagnetic waves

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can travel through vacuums (e.g. heat from sun → earth)

particle model

1. Behaviour of solids, liquids and gasses can be explained by representing them as a group of particles
2. Energy added/taken away from particles affects movement
3. Arrangement + movement of particles affects properties

wavelength

the distance between any one point on a wave and the same point on the next wave (e.g. from crest to crest)

frequency

a measure of how many full waves pass through a single point in a second

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measured in hertz

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shorter wavelength = higher frequency (if same speed)

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relates to the speed + wavelength

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determines the pitch in a sound wave

amplitude

the distance from the middle of the wave (resting point) to the crest or trough

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higher amplitudes = more energy

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determines the volume/loudness in a sound wave

speed

a measure of how fast the wave is travelling

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usually measured in m/s

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varies depending on the medium (travels faster in solids)

velocity

refers to both the speed and direction of a wave

medium

a substance that the wave is travelling through

longitudinal waves

the movement of particles is parallel to the motion of wave (e.g. sound and P-waves)

transverse waves

the movement of particles is perpendicular to the motion of wave (e.g. light and water waves)

crest

the top or highest point above the resting point

trough

the bottom or lowest point from the resting point

compression

the region on a longitudinal wave where the particles are very close together

rarefaction

the region on a longitudinal wave where the particles are very spread out

wave equation

v=λf'

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speed = frequency x wavelength

loudness

determined by the amplitude of a sound wave (larger amplitude = louder sound)

pitch

determined by frequency and wavelength (higher frequency, shorter wavelength = higher pitch)

electromagnetic spectrum

consists of a range of invisible waves

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all EM waves travel at the speed of light (in order of decreasing wavelength)

* radio waves
* microwaves
* infrared waves
* visible light
* ultraviolet light
* x-rays
* γ-rays/gamma rays

reflection

light bounces off an object (e.g. telescopes)

refraction

the bending of light as it passes from one medium to another due to change in speed

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faster in less dense matter (e.g. pencil in water)

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less dense → more dense: refracted towards the normal

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more dense → less dense: refracted away from the noraml

absorption

light is transformed into heat inside an object (e.g. solar cells)

law of reflection

angle of incidence = angle of reflection

normal

an imaginary line that is at an exact 90° from the surface at the point where light strikes

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normally represented by a dashed line

wave

“energy carriers”

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not made of particles

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not all require a medium to travel

light wave

an electromagnetic wave (travels through space at fast speeds)

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1. cannot bend around corners (travels in straight lines)
2. travels fastest in a vacuum, but slow in other mediums

lens

convex lens

a lens that is curved outwards and is thicker in the middle

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causes light rays to converge

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can produce either bigger or smaller images

concave lens

a lens that is curved inwards and is thinner in the middle

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causes light rays to diverge

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produces smaller images

sound wave

longitudinal waves

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can only travel through solid, liquid or gas

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cannot travel through empty space

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produced by all vibrating objects

decibel

a unit used to measure loudness (a normal conversation is about 60 dB)

penetrating power

the ability of each type of radiation to pass through matter

joule

J: a measurement for energy

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the amount of work done when a force of 1N is moved through 1m (1kJ=1000J and 1 calorie=4.2J)

radio waves uses

communication (e.g. television and radio) → transmitted easily through air, do not cause damage to body, can be reflected to change direction

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other: mobile phones, walkie-talkies, satellites

microwaves uses

cooking food → frequencies are easily absorbed by food molecules, internal energy increases (heating)

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satellite communications → pass easily through atmosphere

infrared waves uses

electrical heaters + cookers → frequencies are absorbed by some chemical bonds, internal energy increases (heating)

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infrared cameras → all objects emit infrared light

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other: deep tissue therapy, military technology

visible light uses

fibre optic communications → coded pulses of light travel through glass fibres from source to reciever

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other: vision, photography

ultraviolet radiation uses

sterilising water/hospital + hairdressing equipment → kills bacteria

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good for skin → helps to make vitamin D (but overexposure can also cause skin problems)

ionising radiation (UV, x-rays, γ-rays) uses

UV wavesγ: premature skin ageing, increases risk of skin cancer

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γ-rays: damages/kills body cells, cancer treatment, nuclear power plants

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x-rays: x-rays, security at airport

ionising radiation

can knock electrons from the shells of atoms, turning them into ions

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can lead to mutations in cells → cancer (e.g. UV waves, x-rays, γ-rays)

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a form of energy/nuclear radiation that acts by removing electrons from atoms/molecules

* atoms lose electrons
* charge changes (more positive)
* becomes ions

radio waves

largest wavelength of EM spectrum (up to 1km long)

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lowest energy of EM spectrum (cannot pass through thick material)

microwaves

second lowest energy of EM spectrum

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wavelengths tend to be about 1cm long

infrared light

less energy than visible light

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wavelength of about 0.01mm

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cannot be seen by the naked eye, but can be felt as heat

visible light

only part of the EM spectrum we can see

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white light composed of all the colours of the spectrum

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violet light: smallest wavelength (400nm), most energy

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red light: largest wavelength (700nm), least energy

ultraviolet (UV) light

has lots of energy

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shorter wavelengths than visible light (100nm-10nm)

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can penetrate skin cells and cause cancer

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causes sunburn

x-rays

very energetic

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can pass through soft tissue of the human body

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very short wavelength (1nm-0.1nm)

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cannot pass through bones and teeth (reflected by denser materials)

γ-rays

has the most energy of the EM spectrum

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high frequency

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shortest wavelength (0.000006nm)

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extremely dangerous to humans (can pass through body and cause damage)

α-particle

two protons + two neutrons

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high ionisation density

β-particle

electrons

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low ionisation density

γ-rays and x-rays

electromagnetic waves

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low ionisation density

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high penetrating power

conductor

a material that allows charge or heat to pass through it easily

hertz

a measurement for frequency (Hz)

colour

a property of visible light that depends on its frequency

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lowest frequency of light that we can see is red, and the highest is purple

transmission

the passing of light through a material

diffraction

the spreading of waves as they pass through or around an obstacle

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e.g. a megaphone

scattering

a change in the direction of motion of a particle because of a collision with another particle

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the spreading of a stream of particles or a beam of rays, as of light, over a range of directions as a result of collisions with other particles

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e.g. the prism experiment

shadow

an absence of light

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light blocked by an object

transparent

allowing nearly all light to pass through

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e.g. window

translucent

allowing only some light to pass through

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object appears blurred

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e.g. sunglasses

opaque

not allowing light to pass through

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e.g. a rock