P2 Waves Flashcards
define how energy is transferred through mechanical waves
energy is transferred between 2 points through the vibration/oscillation of air/solid particles through which the energy travels
describe transverse waves
oscillations are perpendicular to direction of energy transfer
eg. EM waves
describe longitudinal waves
oscillations are parallel to direction of energy transfer
eg. sound waves
define amplitude
maximum displacement of a point on a wave from its undisturbed position
(horizontal line to peak)
define wavelength
distance from a point on a wave to the closest equivalent point
(longitudinal: compression to compression / rarefaction to rarefaction)
(transverse: peak to peak)
define frequency
number of waves passing a point per second
measured in Hz (= 1 wave per second)
define wave period
time taken for a wave to complete a full cycle
(one wavelength)
equation for wave period (wavelength)
period = 1 / frequency
(secs) (Hz)
equation for wave speed
wave speed = frequency x wavelength
v = f x λ
(m/s) (Hz) (m)
method of measuring speed of water waves RP (6)
- set up ripple tank: shallow water tank, lamp directly above+downwards, connect power supply+motor circuit, motor on wooden rod
- pour water into tank to 5mm deep, adjust rod so it’s touching water surface
- switch on electric motor+lamp, then adjust until clear+low-frequency waves can be seen on card
- find wavelength: place metre rule perpendicular to waves on card, record how many waves across 100cm, then divide length by no. waves
- find frequency: count number of waves passing a point in 10secs, then divide number by time
- find wave speed: v = f x λ
suitability of method to measure speed of water waves RP
- motor ensures regular ripples are generated - increased accuracy
method of measuring speed of waves through a solid RP (5)
- set up apparatus: attach string to vibration generator (connected to power supply), use a 200g hanging mass and pulley to pull the string taut. place wooden bridge under string near the pulley
- switch on vibration generator, adjust the wooden bridge until clear stationary waves can be seen
- find wavelength: measure across as many loops (half wavelengths) as possible, then divide length by no. loops to find half wavelength, double
- find frequency: equal to the frequency of the power supply
- find wave speed: v = f x λ
suitability of method to find wave speed through a solid RP
- vibration generator ensures regular ripples are generated - increased accuracy
describe EM waves (4)
- transverse
- transfer energy from source to an absorber
- continuous spectrum of long - short wavelength, grouped by wavelength+frequency
- they travel at same speed = 3 x 10⁸ m/s through vacuum/air
describe frequency+energy of waves as wavelength gets shorter
- higher frequency
- higher energy
name EM wave spectrum from long-short wavelength
radio, micro, infrared
visible light
ultraviolet, x-ray, gamma
describe limit of EM waves detectable by humans
our eyes only detect visible light, so detect a limited range of electromagnetic waves
why refraction occurs
when waves travel through one medium to another with different densities
wave speed changes, causing wavelength to change (as directly proportional)
-> wave fronts get closer together as speed decreases
rule of refraction
-> a wave going through a less dense material will get faster + move away from the normal
-> a wave going through a more dense material will slow down + move towards the normal
Faster is Away , Slower is Towards
effect of wavelength on refraction
shortest wavelengths are refracted the most (violet)
what happens when white light is transmitted through a glass prism
colours making up white light have different wavelengths, so also different wave speeds
this means they are refracted at different angles, causing colours to disperse
describe reflection/ absorption/ emission of light radiation for matt+black surfaces
- no visible light wavelengths reflected or transmitted
- therefore all wavelengths absorbed
- and all radiation emitted
describe reflection/ absorption/ emission of light radiation for shiny+white surfaces
- all visible light wavelengths reflected
- therefore no wavelengths absorbed
- and no radiation emitted
why do black/matt surfaces get hot
- black/matt surfaces are good absorbers of light radiation
- short wavelength light radiation (absorbed) transferred to long wavelength infrared radiation (emitted)
- radiation emitted causing surface to heat up
method for investigating effect of surface on infrared absorption/emission RP
- Leslie cube on heat-proof mat, filled with hot water, put lid on
- use infrared detector to measure amount of IR emitted from each side/surface
-> detector must be same distance from each surface
-> give time between readings for detector to settle
describe what radio waves are made up of
oscillating electric/magnetic fields
therefore can be produced by oscillations in electric circuits
describe how radio waves are produced with electricity
- high-frequency AC supplied to a transmitter, causing electrons in the antenna to oscillate
- oscillating electrons produce oscillating magnetic fields aka radio waves (with same frequency as AC)
- when waves reach the receiver they are absorbed, causing electrons in the receiver to oscillate - produces a current of same frequency as the radio waves
factors affecting how dangerous EM waves are (3)
- type of radiation: high frequency wave means high energy so more damage
- size of dose absorbed: higher dose means higher energy so more damage
- tissue which has absorbed the radiation
danger of micro waves for humans
heats water molecules in body cells - can damage/kill them
danger of infrared for humans
felt as heat - can cause skin damage/burns
danger of visible light for humans
can damage eyes - blindness
danger of UV for humans
- cause mutations to DNA - cancer
- cause skin to age prematurely - increased risk of cancer
danger of x-rays for humans
- cause mutations to DNA (ionising) - cell copying errors - cancer
- radiation sickness - organ failure, death
- damages eyes
danger of gamma rays for humans
- cause mutations to DNA (ionising) - cell copying errors - cancer
- radiation sickness - organ failure, death
- damages eyes
define radiation dose
a measure of the risk of harm from an exposure to radiation
depends on: type of radiation / amount absorbed / type of tissue affected
measured in milliSieverts (mSv)
suitability of radio waves for transmitting tv/radio signals +how
they can travel long distances
* long-wave radio signals diffract+follow curvature of the earth - national broadcasting
* short-wave radio signals reflect off the ionosphere - intercontinental broadcasting
range limited by horizon as waves travel in straight lines
suitability of micro waves for transmitting signals to satellites
they are not strongly absorbed by earth’s atmosphere as they have short wavelength, so can reach satellites in space
* waves sent by a transmitter to a receiver on a satellite orbiting earth
* satellite then transmits waves back to earth + picked up by receivers
suitability of micro waves for cooking
- water molecules in food absorb microwave radiation
- water heats up and cooks the food
suitability of xrays for medical imaging
- xrays absorbed by dense body parts (bones) and transmitted through soft body tissues
- scanners can create negative images of internal body parts
suitability of gamma rays for radiotherapy/sterilisation
gamma rays (+ high doses of xrays) can damage/kill living cells as high energy - used to kill cancer cells or bacteria
suitability of infrared for electric heaters/cookers and cameras
- infrared absorbed by surfaces of food/objects - cause heating
- objects emitting infrared can be seen at night using IR cameras
suitability of visible light for fibre-optic communications
- data is coded into light pulses
- light travels down a long fibre by total internal reflection by glass
suitability+process of UV for energy-efficient light bulbs
fluorescent lights absorb UV radiation and emit the energy as visible light
* an electric current is used to excite the gas
* when atoms de-excite they emit UV waves
* the waves are absorbed by the coating on the bulb
* the coating ‘fluoresces’ + emits visible light
effect of changes in nuclei on EM waves
EM waves can be generated or absorbed over a wide frequency range
eg. gamma rays originate from changes in the nuclei of atoms (radioactive decay)
