P6 Flashcards
Describe how energy is transferred in waves
When waves travel through a medium, the particles of the medium oscillate and transfer energy between each other
What direction the waves transfer energy
Direction they are travelling
What is the amplitude of a wave
The maximum displacement of a point on the wave from its undisturbed position
What is the wavelength of the wave
Distance between the same point onto adjacent waves
What is the frequency of a wave, What is it measured in and what is one of these equal to
The number of complete waves passing a certain points per seconds, hertz, one wave Per second
Is the period of a wave and how do you work it out
The amount of time it takes for a full cycle of the wave to pass a points – one over frequency
What are the two types of waves
Transverse and longitudinal
Describe the oscillations in transverse waves
Perpendicular to the direction of energy transfer
What are examples of transverse waves
All electromagnetic waves e.g. light
– ripples and waves in water
– a wave on a string
Describe the oscillations in longitudinal waves
– Parallel to the direction of energy transfer
What is a key characteristic of longitudinal waves
Rarefractions and compressions
What are examples of longitudinal waves
– Soundwaves in air, ultrasounds
– shockwaves e.g. some seismic waves
What is the equation for wave speed in metres per second
Frequency times wavelength in metres
How could you measure the speed of sound
– Attach a signal generator to the speaker – generate sounds with a specific frequency
– used to microphones and an oscilloscope to find wavelength of the sound waves generated
Describe the method of measuring the speed of sound
– Set up oscilloscope so the detected waves at each microphone shown as separate waves
Starts with both microphones next to the speaker, then slowly move on away until the two waves are aligned on the display but have moved exactly one wavelength apart
– measure the distance between the microphones to find out one wavelength
– use the formula to wave speed to find the speed of the sound waves passing through air – frequency is whatever you set the signal generate two – around one kHz
What is the speed of sound is roughly
330 m/s
Describe the equipment for the practical of measuring the speed of water ripples
– Strobe light over water placed in tree over screen
– signal generator attached to dipper – water waves at set frequency
Describe the method of the wave water speed practical
– Dim lights and turn on strobe lights – sea wave pattern made by shadows of Wavecrest sunscreen blowtank
– increased frequency of strobe light until the wave pattern on the screen appears to freeze and stop moving – happens when the frequency of the strobe light is equal to the frequency of the waves
– distance between each shadow and line is equal to one wavelength – measure distance between shadow lines that are 10 wavelengths of parts then divide this distance by 10 defined average wavelength – suitable for measuring small wavelengths
Why is the strobe a suitable piece of equipment in the wave water speeds practical
It allows you to measure a steel pattern instead of a constantly moving one
Describe the equipment for the wave and string experiment
– Attach signal generator to vibration transducer which is attached to string and a pulley on a bench with masses hanging off the end using a clamp and hook
Describe the methods of the wave string practical
– I just frequency setting on the signal generator to change length of we’ve created on string
– keep adjusting the frequency of the signal generator until there appears to be a clear wave- standing wave from resonance
– measure the length of all the half wavelengths on stream in one go then divided by the total number of half wavelengths to get them in half wavelength
– double the value to get a Photo wall wavelength
– frequency of a wave it’s whatever the signal generator is set to
– find speed of a wave by times in the frequency by the wavelength
When in the string wave practical there appear to be one clear wave
When a whole number of half wavelengths fit exactly on the string – if you want at least four or five ideally
What does the frequency you need in a string wave practical depends on
The length of string between the pulley and transducer and the masses you have used
What type are all electromagnetic (EM) waves, what do they do and what are they
– Transverse
– transfer energy from a source to an absorber
Can EM waves travel through a vacuum and why
Yes because they aren’t vibrations of particles, they are vibrations of electric and magnetic fields
Describe the speed of electromagnetic waves
– The same speed through or a vacuum – all the same
What are the seven types of EN waves in order of increasing frequency and decreasing wavelrngth
– Radio waves – microwaves – infrared – visible lights – ultraviolet – x-rays – gamma rays
Why is there such a large range of frequencies in EN waves and what can this explain
They are generated by a variety of changes in atoms and that nuclei e.g. changes in the nucleus of an atom creates gamma rays
– explains why atoms can absorb a range of frequencies – each one causes a different change
What are EM waves and alternating-current made up of
– EM waves – oscillating electric and magnetic fields
– AC – oscillating charges – as they oscillate they produce oscillating electric and magnetic fields i.e. electromagnetic waves
What is the frequency of waves produced equal to
The frequency of the alternating-current
How can you produce radio waves
– Using an alternating-current in an electrical circuit
What is a transmitter
The object in which charges (electrons) oscillate to create the radio waves
What happens when transmitted radio waves reach a receiver
The radio waves are absorbed
What happened to the energy transferred by the waves, What does this cause and describe this
It is transferred to the electrons in the material of the receiver – energy causes the electrons to oscillate and if the receiver is part of a complete circuit it’s generates an alternating currents
– current has the same frequency as the radio waves that’s generated it
What are radio waves
EM radiation with wavelengths longer than about 10 cm
What classes as long wave radio waves, how far can they be transmitted, around what, and why, And what does this make possible
– 1 to 10 km
– from London and received halfway around the world
– around hills, into tunnels and allsorts
– they diffract around the curved surface of the Earth
– For radio signals to be received even if the receiver isn’t in the line of sight of the transmitter
What does shortwave radio signals class as and how can they both be received, why, and what is an example
– 10 m to 100 m
– can be received at long distances from the transmitter
– reflected from the ionosphere
– Bluetooth uses shortwave radio waves to send data over short distances between devices without wires e.g. wireless headsets so you can use your phone whilst driving a car
What is the ionosphere
An electrically charged layer in the earths upper atmosphere
Can medium wave signals reflect of the ionosphere and what does this depend on
Sometimes – depending on atmospheric conditions and the time of day
Describe the radio waves used for TV and FM radio transmissions and what does this mean
– Very short wavelengths
– to get reception you must be in direct sight of the transmitter – signal doesn’t bend or travel through buildings very far
What type of waves are used by satellites
Microwaves
What are examples of satellites
Satellite TV signals and phones
What specificity is a needed the waves in satellites
Microwaves which can pass easily through the earths watery atmosphere
Describe the process of satellite TV
– The signal from a transmitter is transmitted into space
– picked up by satellite receiver dish or between thousands of kilometres above the Earth
– satellite transmits the signal back to earth and different direction where it is received by a satellite dish on the grounds
– slight time delay between the signal being sent and received because of the long distance the signal has to travel
Describe the contrast in waves needed in microwave ovens to microwave is used in satellite
– In communications the microwave is used need to pass through the earths water in the atmosphere
– in microwave ovens the microwaves need to be absorbed by water molecules in the food – so they use a different wavelength to those used in satellite communications
Describe how a microwave oven works
– Microwaves penetrate up to a few centimetres into the foods before being absorbed and transferring energy they are carrying into the water molecules in the food – causing the water to heat up
– the water molecules and transfer this energy to the rest of the molecules in the food by heating – quickly cooks the food
What objects is infrared radiation given out by and what increases it
– All objects
– the hotter the object, the more IR radiation it gives out
What is an example of infrared radiation use and how does this work
– Infrared cameras
– can be used to detect infrared radiation and monitor temperature
– camera detect the infrared radiation and turns it into an electrical signal which is displayed on a screen as a picture
– the hotter an object is, the brighter it appears e.g. energy transfer from the house is thermal energy store can be detected using infrared cameras
– different colours represent different amounts of IR radiation being detected
What are two examples of appliances which use infrared radiation and how do they work
– Toaster – food can be cooked using infrared radiation – the temperature of the food increases when it absorbs radiation
– electric heaters heat to room in the same way – contain long piece of wire that heats up when a current flows through it
– this wire emits lots of infrared radiation and a little visible lights – the wire glows
– emitted infrared radiation is absorbed by objects and the air in the room – Energy is transferred by the infrared waves to the thermal energy stores of the objects causing the temperature to increase
What is a use of visible light, how do they work, why
– Optical fibres – thin glass or plastic fibres that can carry data e.g. from telephones or computers over long distances as pulses of visible light
– work because of reflection – light rays are bounced back and forth until they reach the end of the fibre
– light is not easily absorbed or scattered as it travels along a fibre
What is fluorescent and why do fluorescent colours look so bright
– Property of certain chemicals where ultraviolet radiation is absorbed and then visible light is emitted
– they actually emit light
Describe uses of ultraviolet radiation
– Fluorescent lights – generate UV radiation which is absorbed and readmitted as a visible light by a layer of phosphorus inside of the bulb– Energy-efficient so good to use when light is needed for long periods e.g. in a classroom, emits very little UV – safe
– security pens can be used to mark property with your name – under UV light the ink will blow but it is invisible otherwise – can help please identify property if stolen
– UV light produced by sun – gives people suntan
– sat tanning salons where UV lamps are used to give them artificial suntan- overexposure can be dangerous
What is an example use of x-rays and how does this work
– radiographers in hospitals take x-ray photographs of people to see if they have any broken bones
-X-rays pass easily through flesh but not so easily through denser material such as bones or metal – amount of radiation that is absorbed or not absorb that gives you an x-ray image
How come x-rays and gamma rays be used
– Radiotherapy – treating people with cancer
– high doses of these Waves kill all living cells – carefully directed towards cancer cells to avoid killing too many normal, healthy cells
What is another medical use of gamma radiation and why is it well suited to this
– Medical traces – a gamma omitting source is injected into the patient, and its progress is followed around the body
– well suited because it can pass out through the body to be detected
What is used when handling X and gamma rays and why
– Can be harmful
– radiographers where lead aprons and stand behind a lead screen or leave the room to keep their exposure to a minimum
Describe different damages done by EM radiation (low/high frequency)
– Low frequency – e.g. Radio waves – don’t transfer much energy so mostly passed through soft tissue without being absorbed
– high-frequency – UV, x-rays, gamma rays – transfer lots of energy and so can cause lots of damage
How can UV radiation be harmful
– Damages surface cells – can lead to sunburn and cause skin to age prematurely – can cause blindness and increased risk of skin cancer
What are x-rays and gamma rays examples of and what can be side-effects of this and why
– Ionising radiation
– carry enough energy to not electrons off of atoms
– can cause gene mutations also distractions and cancer
What is needed before using UV radiation, x-rays and gamma rays
– People look at whether benefits outweigh the health risks
What is radiation dose measured in, what is this a measure of and what is its not
– Sieverts
– measure of risk of harm from the body being exposed to radiation not a measure of the total amount of radiation that has been absorbed
What does the risk of radiation depend on
The total amount of radiation absorbed and how harmful the type of radiation is
How does a CT scan work, what is the difference of radiation dose the head and chest and what does this mean
– Uses x-rays and a computer to build up a picture of the inside of a patient’s body
– head – to millisieverts, chest – 8 mSv
– if a patient had a CT scan on their chest they are four times more likely to suffer damage to their genes – added risk of harm is four times greater than if they had a head scan
Describe reflection in white and black objects
– Whites – reflect all of the wavelengths of visible light equally
– black – absorb all wavelength of visible light – your eyes see black is the lack of any visible light – the lack of any colour
Describe transparent and translucent objects
They transmit light i.e. not all like that hits the surface of the object is absorbed or reflected – some can pass through
Describe what happens to some wavelengths in transparent and translucent objects and what is there colour related to
– Some wavelengths of light may be absorbed or reflected by transparent and translucent objects – its colour is related to the wavelengths of light transmitted and reflected by it
What are all objects continually emitting and absorbing, where is it emitted from and what controls how much is emitted
– Infrared radiation
– the hotter an object is the more infrared radiation it radiates
– emitted from the surface of an object
Describe the infrared radiation/absorption from an object that is hotter than its surroundings
Hotter – emites more Infrared radiation than it absorbs as it cools down e.g. a cup of tea left on a table
Cooler – absorbs more infrared radiation than it omits as it warms up e.g. cold glass of water on a sunny day
Describe infrared radiation in objects that are at a constant temperature
Emit infrared radiation at the same rate they are absorbing it
Describe another factor affecting the absorption/omission of infrared radiation and give examples
– Some colours and surfaces absorb and emits radiation better than others
– e.g. black surface better at absorbing and emitting radiation than a white one
– Matt service better at absorbing and emitting radiation than a shiny one
Described the practical equipment for investigating the absorption
– two identical metal plates, with wax and ball bearing attached, one with silverside and one with Matt black sides
– Bunsen burner in between
Describe how the wax Ball practical works
– The sides of plates facing towards the flame have different surface colour
– as the heat up, one will fall off earlier
– one with black plate should fall first as black surface absorbs more infrared radiation – transferring more energy to the thermal energy store of the wax – means the wax on the black Plate melts before the max on the silver plate
What is a Leslie cube and what can it be used to investigate
– A hollow, watertight, metal cube made of substance e.g. aluminium whose four vertical faces have different surfaces e.g. Matt black paint, Matt white paint, shiny metal and stone metal
– investigate infrared radiation emitted by different surfaces
Describe how you would investigate emission using a Leslie cube
– Please empty Leslie cube on a heat proof Matt
– boil water and fuel cube with it
– wait for cube to warm up then hold a thermometer against each of the four vertical faces of the tube – should find that all our same temperature
– hold infrared detector at set distance e.g. 10 cm away from one of the cubes vertical faces and record the amount of infrared radiation it detects
– repeat measurements for each of the cubes faces
– make sure you position detector at same distance from Cuba each time
What should you find with the Leslie cube practical and what do you need to do with the results
– You should detect more infrared radiation from the black surface and Matt surface, and less from the white surface and shiny surface
– do it more than once to make sure results are repeatable
What are hazards from the Leslie cube practical
Boiling water, full kettle
What is a perfect black body
An object that absorbs all of the radiation that hits it – no radiation is reflected or transmitted
Describe the omission in perfect black bodies
– The best possible emitters of radiation – all objects emit electromagnetic radiation due to the energy in their thermal energy stores, radiation isn’t just in the infrareds part of the spectrum – covers a wide range of wavelengths and frequencies
What does the intensity and distribution of wavelengths emitted by an object depends on
The objects temperature
What is intensity
The power per unit area i.e. how much energy is transferred to a given area in a certain amount of time
What happens as the temperature of an object increases
The intensity of every emitted wavelength increases
What is the peak wavelength and what causes it to decrease
– The wavelength with the highest intensity
– the intensity increases more rapidly for shorter wavelengths than longer wavelengths
What happens to the peak wavelength as the object gets hotter
It’s decreases
What causes an increase in local temperature during the day on Earth
Lots of radiation like light is transferred to the Earth from the Sun and absorbed
Describe radiation at night
Less is absorbed that is being omitted causing a decrease in the local temperature
What does the overall temperature of the Earth depends on
The amount of infrared radiation it reflects, absorbs and emits
Describe different ways which radiation is reflected and emited
–some reflected by atmosphere, clouds and earths surface
– some emitted by the atmosphere
What happens to some of the radiation which is omitted by the surface of the Earth
Reflected or absorbed and later emitted by the clouds
What different things absorb radiation on earth
Atmosphere, clouds and earths surface
What can changes to the atmosphere cause
A change to the earths overall temperature
Describe global warming in terms of radiation
– If the atmosphere starts to absorb more radiation without limiting the same amounts, the overall temperature will rise until absorption and emission are equal again
What are soundwaves caused by, what are these passed through as and what wave type are they
– Waves caused by vibrating objects
– vibrations are passed through the surrounding medium as a series of compressions and rarefactions
– longitudinal
Describe the general speed of sound waves in different mediums
Faster in solids and liquids, fast in liquids and gases
How does a sound waves travel through a solid
Causes the particles in the solid to vibrate
How does a speaker work
– Paper diaphragm and a speaker vibrates back-and-forth which causes the surrounding air to vibrate creating compressions and rare fractions
– soundwave is created is
– soundwaves travels through as a series of compressions and rarefactions
– when it hits a solid object the Air particles cause hitting the object (the pressure) causes the particles in the solid to move back on the fourth – vibrates
– these particles hit the next particles in line and so on passing the soundwave through the object as a series of vibrations
Can sounds particles travel in space and why
No – it is mostly a vacuum so there are no particles to move or vibrate
Describe the process of hearing a sound
– Sound waves that reach your eardrum can cause it to vibrate
– these vibrations are passed on to tiny bones in your ear called ossicles, through the semicircular canals and to the Cochlea
– The cochlea Turn these vibrations into electrical signals which gets sent to your brain and allow you to sense i.e. hear the sounds
What is the range of frequencies which humans can hear
20 Hz to 20 kHz
How do microphones work
– Soundwaves cause a diaphragm to vibrate and this movement is transferred into an electrical signal
– can pick up soundwaves outside of human range but if you tried to listen you probably wouldn’t hear anything
What is human hearing limited bye
The size and shape of our eardrum as well as the structure of all of the parts within the air that vibrate to transfer the energy from the soundwaves
What are echoes
Reflected sound waves off hard flat surfaces
What changes are sound waves refract from entering different media and why
– As they enter denser material they speed up – its wavelength changes but its frequency remains the same – speeds must also change
