Electromagnetic waves and sound waves Flashcards
transverse wave
vibrations are perpendicular to the direction of wave motion
longitudinal waves
vibrations are parallel to the direction of wave motion
waves
transfer of energy by vibrations without a medium
examples of transverse waves
electromagnetic spectrum, water waves, seismic S-waves, light waves
examples of longitudinal waves
sound waves, seismic P-waves
echo
the reflection of sound waves
wave speed formula
speed = frequency x wave length
electromagnetic waves
Radio waves, microwaves, infrared waves, visible light, ultraviolet, xrays, gamma rays
largest wavelength, lowest frequency (EM)
Radiowaves
smallest wavelenth, largest frequency (EM)
Gamma rays (y)
speed of EM waves in vacuum
3.0 x 10^8m/s
Use of radio waves
communication and broadcasting (TV and Radio)
Use of microwaves
Heating food, communication (moblie phones, wifi, satellites)
How do microwaves work (in terms of satellite communication)?
Their shorter wave length means they can penetrate the atmosphere and reach the orbiting satellites. Then, the wave will be reflected to where needed.
How do radiowaves work (in terms of communication)
They reflect off the ionsphere and to a place in the line of sight
How do microwaves heat food?
The waves cause the water molecules to vibrate, producing heat energy to cook food.
Infrared uses
electrical heaters and conventional ovens/grills, heat detectors, tv remotes, thermal imaging and intruder alarms
Visible light uses
photography, sight, optic fibres
How does visible light make optic fibres possible?
Visible light can go through total internal reflection, making it reflect back into the fibre continuously
Ultraviolet uses
energy efficient light bulbs, suntanning, curing inks and resin, sterilisation, fake bank note checking,
How does ultraviolet waves make energy efficient light bulbs - fluorescent light bulbs?
An electric current excites the gas, moving its atoms to a higher energy level. When they ‘de-excite’ - they emit UV waves. These are absorbed by the coating on the bulb and emit fluorescence.
Xray uses
medical imaging, airport secruity, and industry
How do xrays allow medical imaging?
X-rays are able to penetrate soft tissue but are absorbed by bones. A photographic plate is blackened where it receives X-rays, and the bones leave a white “shadow”.
Gamma ray uses
sterilisation of medical tools and food, treating cancer
What do bluetooth devices use?
Low energy radio waves or microwaves, they can pass through walls but the signal is weakened doing so.
What do mobile phones use?
microwaves, because they can penetrate some walls and only require a short aerial for transmission and reception
What waves do optical fibres use?
Visible light and infrared. Visible light and short wavelength infrared can carry high rates of data.
speed of sound in air
330 - 350 m/s
relative speed of sound in gases, liquids and solids
Fastest in solids, then liquids and slowest in gases. Because particles are closer to eachother in solids.
How does increased temperature effect speed of sound?
Increased temperature increases speed of sound as particles have higher kinetic energy and so there is a higher rate of collisions, easier energy transfer
difference between digital and analogue signal
Analogues signal changes in frequency and amplitude all the time in a way that matches the changes in the voice or music being transmitted.
Digital signals have only two values - 0 and 1.
two ways sound can be transmitted
as a digital or analogue signal
benefits of digital signaling
increased rate and range of transmission due to accurate signal regeneration
What waves are used for communication with artificial satellites
microwaves:
a) some satellite phones use low orbit artificial satelites
b) some satellite phones and direct broadcast satellite television use geostationary satellites
what do some satellite phones use?
low orbit artificial satellites
what do some satellite phones and direct broadcast satellite television use?
geostationary satellites
geostationary satellite
a satellite that appears to be located at a fixed point in space when viewed from the earth’s surface
how is sound produced?
to produce sound an object needs to be vibrating and pushing on the air around it to generate the longitudinal wave that is transmitted through the air (or water)
compression
region in which the particles of the wave are closest to each other
rarefraction
region in which the particles of the wave are far from eachother.
increase in amplitude increases…
volume
increase in frequency increases..
pitch
ultrasound
a sound with a frequency higher than 20 kHz
uses of ultrasound (non-destructive)
testing of materials, medical scanning of soft tissue and sonar
how does medical scanning with ultrasound work?
A small transducer (probe) transmits sound waves into the body and records the waves that echos back. Sound waves travel into the area being examined until they hit a boundary between tissues. At these boundaries some of the sound waves are reflected back to the probe, while others travel further until they reach another boundary and are reflected back. Since the speed, direction, and distance sound waves travel differ depending on the boundary they run into, a computer can interpret this information as a two-dimensional image on a screen.
(DONT NEED THIS MUCH DETAIL)
how does ultrasound work in terms of testing materials?
a probe/transducer sends sound waves through the material they want to test. if there are no defects, the sound waves will pass through, but if the sound waves hit a defect they will bounce of it, indicating its prescence
