Waves Flashcards
Define transverse wave
A wave which travels at 90 degrees to direction of energy transfer
Define longitudinal wave
A wave which travels parallel to direction of energy transfer
Examples of transverse waves
Light waves, Surface water waves
Examples of longitudinal waves
Sound waves, pressure waves
What do waves transfer?
Waves transfer energy but NOT matter
Amplitude
The point of max. displacement from equilibrium position
Frequency
Number of waves produced/passing a particular point per second
Time period
The time taken for a wave to complete 1 cycle
Wavelength
The distance between a point on one wave to the same point on the next wave, eg peak to peak
What formula links time period and frequency?
T = 1/f OR F = 1/T
What formula links wavespeed, wavelength and frequency?
Wavespeed = frequency x wavelength
What is the unit of wavelength?
meters, m
What is the unit of time period?
Seconds, s
What is the unit of speed?
meters per second, m/s
What is the unit of frequency?
Hertz, Hz
What determines the pitch of a sound?
The frequency
What determines the loudness of a wave?
The amplitude
If a wave has a low frequency and a low amplitude, what is the pitch and loudness like?
Low pitch, low volume
If a wave has high frequency and high amplitude , then what’s the wave like?
High pitch, high volume
If a wave has low frequency and high amplitude, what’s the wave like?
Low pitch, high volume
If a wave has a high frequency and a low amplitude, what’s the wave like?
High pitch, low volume
Speed of sound in air
330m/s
Speed of sound in water
1500m/s
Speed of sound in steel
5000m/s
How does medium affect the speed of sound?
- As density of medium increases, so does speed of sound.
- Sound travels fastest in a solid where the particles are close together (as solids are the most dense) and they can transfer vibrations faster between particles
- in gas + liquids, particles are further away (less dense) so vibrations take longer to pass between particles
What is the range of human hearing?
20-20,000Hz
What are the uses of ultrasound?
- prenatal ultrasound scans
- crack detection in machinery
- breaking kidney stones
How is ultrasound used in prenatal scans?
- probe emits + receives the waves
- ultrasound transmits through the tissue
- the waves are reflected whenever there is a change in density to create an image on the screen
- the time taken to recieve echo x speed of sound = depth of fetus
Which is done multiple times to form image
How is ultrasound used in crack detection in machinery?
- the transceiver transmits ultrasound through the metal
- waves are reflected back to transceiver when the crack is detected to see how deep in the crack is
- time taken and speed through medium is multiplied to find how deep the crack is
Order of waves in EM spectrum
Radiowaves, Microwaves, Infrared, Visible, Ultraviolet, X-rays, Gamma rays
Common properties of all EM waves
- all are transverse
- all travel at 3 x 10^8m/s in a vacuum
- all can be reflected, refracted and diffracted
Uses of Radiowaves
- radio + TV signals
- long wave radio signals are broadcasted by transceivers and and are reflected by the atmosphere around the world to other transceivers
Uses of microwaves
- cooking wood w large water content + mobile & satellite comms
- water molecules in food absorb large amts of microwaves so food gets hot and cooks
- are able to transmit though atmosphere to satellites
Uses of infrared
- cooking food on grills + short range data comms (TV remotes)
- thermal energy emits from grill into air and absorbed by food
- waves transmit through air from remote, and energy absorbed quickly so are used for short distances
Uses of visible light
- traffic systems + glasses/ contacts
- coloured light transmits through the air and is absorbed by eyes
- refraction of light through curved glass is absorbed by eyes to correct vision
Uses of ultraviolet
- security tagging banknotes, sterilising, tanning
- fluorescent ink absorbs UV and reflects white light into eyes
- bacteria absorbs UV and is killed
- suncream absorbs and/or reflects UV instead of it being absorbed by skin
Uses of X-rays
- airport security scanners, scanning of skeleton
- waves are transmitted through bags and picked up by a receiver to form an image
- transmitted through body tissue but reflected by bones so the film has a shadow of the bones to identify cracks
Uses of gamma rays
- radiotherapy cancer treatment, medical tracer
- high energy waves are directed to the cancer which absorbs them and the cells die
- patient is injected w radioactive tracer which absorbs gamma so blockages can be seen during a scan
What 3 parts of the EM spectrum are ionising?
UV, X-rays and gamma rays
Why are UV, X-rays and gamma rays ionising?
have the highest frequency = highest energy which means that they’re more dangerous
Why is ionising radiation dangerous?
- overexposure of ionising radiation causes atoms in cells to lose electrons, ionising them
- this can mutate cells and lead to cancer
Why is overexposure to visible light dangerous?
harms the eyes by damaging the retinas
Why is overexposure to infrared dangerous?
Burns the skin and tissue
What is the Doppler effect?
The apparent shift in wavelength when a source moves relative to an observer. As wavelength decreases, frequency increases. The faster the sourceis moving relative to the observer, the more pronounced the difference in pitch and volume.
How does the Doppler effect work?
- as the source gets closer to the observer, there is an apparent increase in frequency which results in a higher volume and pitch, called blue shift
- as the source moves away from the observer, there is an apparent decrease in frequency which results in a lower volume and pitch, called red shift
