the oscillations (vibrations) are perpendicular (at 90º) to the direction of energy transfer.

• electromagnetic waves e.g. light
• ripples & waves in water
• a wave on a string

• set up oscilloscope so detected waves at each microphone are shown as separate waves.
• start with both microphones next to speaker then slowly move one away until the two waves are aligned on the display but have moved exactly one wavelength apart.
• measure distance between microphones to find one wavelength (λ)
• use v = fλ to find speed of the sound waves passing through the air, the frequency is what the signal generator was set to (around 1kHz)
• speed of sound in air 330 m/s - results should roughly agree.

• using a signal generator attached to the dipper of a ripple tank, you can create water waves at a set frequency.
• use lamp to see wave crests on a screen below tank.
• distance between each shadow line is equal to one wavelength. measure distance between shadow lines that are 10 wavelengths apart, divide this distance by 10 to find average wavelength - good method for measuring small wavelengths
• use v = f λ to calculate wave speed
• suitable for investigating waves as it allows you to measure the wavelength without disturbing the waves.
  
  

dim lights. dipper dips in & out of water producing ripples.

• when signal generator & vibration transducer turned on, string starts to vibrate.
• adjust frequency of signal generator until there is a clear wave on the string. frequency needed depends on length of string between pulley & transducer & the masses used.
• measure wavelength of waves accurately by measuring the lengths of e.g. 4 or 5 half-wavelengths (as many as poss.) at once then divide to get mean half-wavelength, double this to get full wavelength.
• frequency of wave is what signal generator is set to.
• find speed with v = fλ
  
  

suitable for investigating waves on a string as it's easy to see & measure wavelength.

angle of incidence = angle of reflection

• ray is perpendicular to wave's wave front
• angle of incidence is angle between incoming wave & normal.
• angle of reflection is angle between normal & reflected ray
• normal is imaginary line perpendicular to surface at point of incidence (where wave hits boundary), shown as a dotted line

when waves arrive at a boundary between 2 different materials:

• waves are absorbed by the material the wave is trying to cross into, transferring energy to the material's energy stores.
• waves transmitted - carry on travelling through new material which often leads to refraction.
• waves are reflected.

happens when a wave is reflected in a single direction by a smooth surface e.g. when light is reflected by a mirror you get a clear reflection.

happens when the normal is different for each incoming ray, so angle of incidence is different for each ray --> angle of incidence = angle of reflection

when light is reflected by a rough surface, the surface appears matte (not shiny) & you don't get a clear reflection of objects

• the frequency of the waves produced is equal to the frequency of the alternating current.
• radio waves can be produced using an alternating current in an electrical circuit.
• charges (electrons) oscillate to create the radio waves in a transmitter.
• when transmitted radio waves reach a receiver, the radio waves are absorbed.
• the energy carried by the waves is transferred to the electrons in the material of the receiver.
• this energy causes the electrons to oscillate & if the receiver is part of a complete electrical circuit, it generates an alternating current.
• this current has the same frequency as the radio waves that generated it.

• medium-wave signals can also reflect from the ionosphere depending on atmospheric conditions & the time of day.

satellite TV - signal from a transmitter is transmitted into space where it is picked up by the satellite receiver dish orbiting thousands of kilometres above the Earth.
the satellite transmits the signal back to Earth in a different direction where it is received by a satellite dish on the ground - slight time delay between signal being sent & received because of the long distance the signal has to travel.

the water molecules then transfer this energy to the rest of the molecules in the food by heating - quickly cooks the food.

• electric heaters can heat a room as they contain a long piece of wire that heats up when a current flows through it. the wire then emits lots of IR radiation (& a little visible light, the wire glows).
• the emitted IR radiation is absorbed by objects & the air in the room - energy is transferred by the IR waves to the thermal energy stores of the objects, causing their temperatures to increase.

• they work because of reflection. the light rays are bounced back & forth until they reach the end of the fibre.
• visible light used.
• light is not easily absorbed or scattered as it travels along a fibre.

UV radiation is produced by the Sun & exposure to it gives people a suntan.
in tanning salons UV lamps are usd to give people an artificial suntan however overexposure to UV radiation can be dangerous.

• security pens can be used to mark property with your name. under UV light the ink will glow (fluoresce) but is invisible otherwise - help police to identify your property if it is stolen.

used to treat people with cancer (radiotherapy) as high doses of these rays kill all living cells - so they are carefully directed towards cancer cells to avoid killing too many normal, healthy cells.

gamma radiation can be used as a medical tracer where a gamma-emitting source is injected into the patient & its progress is followed around the body.
↪ gamma radiation is well suited to this as it can pass out through the body to be detected.

X-rays & gamma rays can be harmful to people so radiographers wear lead aprons & stand behind a lead screen or leave the room to keep their exposure to a minimum.

the brighter bits are where fewer X-rays get through - this is a negative image - the plate starts off all white.

there is a principal focus on each side of the lens.
the distance from the centre of the lens to the principal focus is the focal length.

• an object at 2F (2 principal focuses away) will produce a real, inverted image the same size as the object & at 2F.
  
  • between F and 2F, it will make the real, inverted image bigger than the object and beyond 2F.
  • an object nearer than F will make a virtual image the right way up, bigger than the object, on the same side of the lens. (further from object)

colours can mix together to make other colours. the only colours that can't be made by mixing are the primary colours: red, green & blue.
when all of these colours are put together, white light is created.

white objects reflect all of the wavelengths of visible light equally.

opaque objects do not transmit light - when visible light waves hit them, they absorb some wavelengths of light & reflect others.

• the colour of an opaque object depends on which wavelengths of light are most strongly reflected.
• for opaque objects that aren't a primary colour, they may be reflecting either the wavelengths of light corresponding to that colour OR the wavelengths of the primary colours that mix together to make that colour.

black objects absorb all wavelengths of visible light - the eyes see black as the lack of any visible light (i.e. the lack of colour).

some wavelengths of light may be absorbed or reflected by transparent & translucent objects - its colour is related to the wavelengths transmitted & reflected by it.

if the object was e.g. red (of any colour not made from blue light), the object would appear black when viewed through a blue filter. All of the light reflected by the object is absorbed by the filter.

filters that aren't for primary colours let through both the wavelengths of light for that colour AND the wavelengths of the primary colours that can be added together to make that colour.

• don't move the cube when it is full of boiling water as you might burn your hands + be careful when carrying the kettle.

the intensity & distribution of the wavelengths emitted by an object depends on the object's temperature.
intensity is the power per unit area i.e. how much energy is transferred to a given area in a certain amount of time.

• as the temperature of an object increases, the intensity of every emitted wavelength increases but the intensity increases more rapidly for shorter wavelengths which causes the peak wavelength (highest intensity) to decrease.

overall, the temperature of the Earth stays fairly constant.

changes to the atmosphere can cause a change to the Earth's overall temperature - if the atmosphere starts to absorb more radiation without emitting the same amount, the overall temperature will increase until absorption & emission are equal again (global warming).

electrical devices can be made which produce electrical oscillations over a range of frequencies, these can be converted into mechanical vibrations to produce sound waves beyond the range of human hearing - ultrasound (frequencies higher than 20kHz).

a pulse of ultrasound can be pointed at an object & wherever there are boundaries between one substance & another, some of the ultrasound gets reflected back.
↪ the time it takes for the reflections to reach a detector can be used to measure how far away the boundary is.

• ultrasound waves can pass through the body, but whenever they reach a boundary between two different media (like fluid in the womb & the skin of the foetus) some of the wave is reflected back & detected.
• the exact timing & distribution of these echoes are processed by a computer to produce a video image of the foetus.
• no one knows if ultrasound is safe in all cases but X-rays would be more dangerous.

• ultrasound can find flaws in objects such as pipes or materials like wood or metal.
• ultrasound waves entering a material are reflected by the far side of the material.
  
  • if there is a flaw e.g. a crack inside the object, the wave will be reflected sooner.

echo sounding uses high frequency sound waves (including ultrasound) & is used by boats & submarines to find out the depth of the water they are in or to locate objects in deep water.

when a wave arrives at a boundary between materials it can:

• be completely reflected or partially reflected.
• continue travelling in the same direction but at a different speed
• refracted
• or absorbed

studying the properties & paths of waves through structures can gives clues to some of the properties of the structure that can't be seen by the eye.

when seismic waves reach a boundary between different layers of material (which have different properties like density) inside the Earth, some waves are absorbed & some are refracted.

• if the waves are refracted they change speed gradually, resulting in a curved path but when the properties change suddenly, the wave speed changes abruptly & the path has a kink.

P waves are longitudinal, travel through solids & liquids & travel faster than S-waves

S-waves are transverse, can't travel through liquids (or gases) & are slower than P-waves.