waves Flashcards
what is amplitude
maximum displacement from rest position. larger the amplitude the more energy a wave carries
what is wavelength
distance between two equivalent points on adjacent waves
what is frequency
number of waves passing a point each second
what is period
the time needed for once complete cycle of vibration to pass a given point
what is the correlation between frequency and period
as the frequency of a wave increases the period of a wave decreases
equation for period
period t (seconds) = 1 divided by frequency (Hz)
wave speed equation
wave speed = frequency x wavelength
what are electromagnetic waves
electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber
properties of electromagnetic waves
reflect refract diffract absorb transmit
how do electromagnetic waves differ from other waves
because they can travel through a vacuum
they form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum
what are waves in electromagnetic spectrum grouped in
grouped in terms of frequency and wavelength
from long to short wavelength or low to high frequency the order of electromagnetic spectrum is
radio waves microwaves infrared visible light ultraviolet xrays gamma rays
radio waves in communication long and short
transfer energy: short radio wave (10m-100m) can be sent over long distances but have to be reflected of the earths atmosphere (ionosphere)
long radio waves (1-10km) waves can diffract (bend) around earths surface
how are radio waves produced
radio waves are made by oscillating electric and magnetic fields
AC current creates the oscillating electric and magnetic fields which creates radio waves in a transmitter
receiver absorbs radio waves and the energy is transferred to the elections in material of receiver
the energy absorbed causes the electrons to oscillate and generates an alternating current
microwaves used by satellites
microwaves are used as they can pass through the earths watery atmosphere
transmitter sends information into space to a satellite
the satellite transmits signal back to earth in a different direction
received by a satellite dish
time delay between signal being sent and received
microwaves in microwave ovens
microwaves in a microwave oven hv a different wavelength compared to communication microwave
therefore microwaves are absorbed by water molecules in food
microwaves penetrate a few cm into the food before being absorbed and transferring the energy to the water molecules
the water molecules transfer the energy to rest of the molecules in the food
causes the food to heat up
required practical : measuring infrared radiation
- place an empty leslie cube on heatproof mat
- boil water in a kettle and fill cube w boiling water
- wair a while for the cube to warm up then hold a thermometer against each of 4 vertical faces of the cube. all 4 faces should be same temp
- hold an infrared detector a set distance away from one of cubes vertical faces and record the amount of IR radiation it’s detects
- repeat the measurement for each of cubes vertical faces. make sure you position the detector at the same distance from the cube each time
- you should find that you detect more infrared reaction from the black surface than the white one and more from matt surfaces than shiny ones
- as always you should do the experiment more than once to make sure results are repeatable
- be careful when doing experiment - don’t move cube when it’s full of boiling water you nufnt burn your hands
dangers of EM waves
UV radiation damages surface cells leads to sunburn and causes skin to age prematurely
serious effects - blindness and increase risk of skin cancer
x rays and gamma rays are ionizing radiation (ability to knock electrons of their atoms)
cause gene mutations , cell destruction and cancer
radiographers have to wear lead apropos to reduce risk of x ray wxposure
what do waves do
transfer energy from one place to another
what are longitudinal waves
particles move side to side - oscillations are parallel to the direction of energy transfer. they show areas of compression and rare fraction sound waves travelling theougj air are longitudinal
what are transverse waves
oscillations are perpendicular (90 degrees) to the direction of the energy transfer
investigating waves required practical
- pour water to a depth of 5mm into tank
- adjust height of wooden rod so that it touches the surface of the water
- switch on overhead lamp and electric motor
- adjust speed of moter as low frequency waves need to be produced
- adjust height of lamp so pattern can be clearly seen on card on floor
- place a meter ruler at right angles to the wave shown in pattern on the card. measure across as many waves as possible then divide length by number of waves to give wavelength of waves
- count number of waves passing a point in latter on 10s then divide number of waves by 10 to give frenquchcy
- calculate speed of waves using equation wave speed = frequency x wavelength
what type of waves are sound waves
longitudinal
what kind of waves are water waves
transverse
what do longitudinal waves show areas of
compression and rare fraction
what emits more IR radiating and what absorbs more
hotter objects than surrounding EMITS more IR radiotion (cools down )
objects cooler than surrounding ABSORB more IR radiation and warm up
what surfaces are btr at emitting radiation
black and matt surfaces are btr at emitting & absorbing radiation compared to white to give maximum rate of energy transfer
refraction of waves
when a wave crosses a boundary between two materials it changes velocity. if the wave is travelling at an angle it changes direction - it is refracted
what is optical density
optical density of a material is the measure of how quickly light can travel though it. the higher the optical density the slower the light wave travels
