P2 - Waves Flashcards
Describe the differences between transverse and longitudinal waves
- Transverse waves (eg water waves) oscillations are perpendicular to direction of energy transfer
- Longitudinal waves (eg sound) oscillations are parallel to energy transfers
What is frequency?
number of waves passing a fixed point per second, measured in Hertz (Hz)
What is amplitude?
maximum displacement of any particles for undisturbed position (m)
What is wavelength?
the distance from one point on a wave to the equivalent point on the next wave (m)
What is a wave period?
time taken for one complete oscillation (s)
What happens when waves pass between different mediums?
- wavelength changes
- frequency doesn’t change because same amount of waves are still being produced per second
- speed and wavelength are directly proportional
What happens when waves reach boundary between two medium?
reflected, refracted, absorbed, transmitted
What is the refractive index?
The way in which a material affects refraction
- low to high RI bends towards normal
- high to low RI bends away from normal
Why does refraction happen?
difference of wave speed in different mediums
What happens when a light wave enters a medium, at an angle, where it travels slower?
- first part of wave slows down
- rest of wave continues at high speed
- changes direction towards normal
What is the range of human hearing?
20 Hz to 20kHz (20 000Hz) - frequencies at which the ear drum can vibrate
Why can’t ultrasound waves be heard by humans?
frequency higher than 20kHz
What happens when an ultrasonic wave meets a boundary between two mediums? How can this be used?
- partially reflected
- helps find how far away a boundary is, measure time taken for ultrasonic wave to return to detector
How are ultrasound waves used in industry?
- defects in materials (cracks, air bubbles, corrosion)
- medicine (pre-natal scans, kidney stones, tumours, images of damaged ligaments or muscles)
What is echo sounding?
use of ultrasonic waves for detecting objects in deep water and measuring water depth
How does echo sounding work?
- ultrasonic pulse see in to water, reflected back when it hits a surface
- time between pulse being send and reflected detected can be used to calculate distance (remember to /2 as it is in both directions)
What is the speed of sound in water?
1500m/s
What are the 2 types of seismic waves?
p-waves (primary)
s-waves (secondary)
Describe P-waves
- longitudinal
- speed of sound
- twice as fast as s-waves
- different speeds through liquids and solids
Describe s-waves
- transverse
- can’t travel through liquids
How can seismic waves be used to locate earthquakes and different materials they have travelled through?
difference in time of arrival of P and S waves at different detectors
In terms of seismic waves, what happens during an earthquake?
- seismic waves travel outwards from earthquake and can travel all the way through earth
- seismic waves travel in a curved path due to earth increasing in density with depth
- detectors placed around the earth measure when and where different waves around
What evidence is given by the s-wave shadow zone?
- s waves can’t travel through liquid outer core
- large shadow zone on opposite side of earth where earthquake originates
- this shadow zone shows size of earth’s core
What evidence is given by the p-wave shadow zone?
- able to travel through liquid outer core
- refracted at boundary between semi solid mantle and liquid outer core
- refract again and boundary between liquid outer core and solid inner core
- refractions = shadow zones
- determines size and composition of inner and outer core
Describe EM waves
- transverse
- same velocity in air or vacuum (speed of light)
- wavelength affects how it is absorbed, transmitted, reflected or refracted, changing its uses
Recall the order of the electromagnetic spectrum from low frequency, long wavelength to high frequency, short wavelength
radio waves microwaves infrared visible light ultraviolet x rays gamma
What are the uses of radio waves and why?
- tv, radio, bluetooth
- low energy so not harmful
What are the uses of microwaves and why?
- satellite, cooking
- travel in straight lines, ideal for transmitting donald to satellites in orbit and back down to receivers
What are the uses of infrared and why?
- heaters, cooking, camera
- glow red as electricity flows, transmits infrared energy absorbed by food and converted back into heat
What are the uses of visible light waves and why?
- fibre optics
- visible light travels down optical fibres from one end to the other without being lost through the sides
What are the uses of UV light waves and why?
energy efficient life bulbs (UV produced by gas in bulb, absorbs by coating on bulb which fluoresces)
security marking, sun beds
What are the uses of x-rays waves and why?
-medical imaging and treatment
can penetrate soft tissue and bone, showing shadows where bones are
What are the uses of gamma ray waves and why?
sterilising food, treating tumours
most energetic of all waves so can destroy bacteria and tumours
What are radio waves caused by?
oscillations in electrical circuits (alternating current)
What does frequency of radio wave depend on?
frequency of electrical oscillation
How is a radio signal received?
Radio waves absorbed by a conductor with same frequency as the wave
How can changes in atoms or nuclei generate or absorb EM waves?
- electrons moving between energy levels due to heat or electrical energy
- nucleus of an atom generates wave (unstable nucleus emits excess gamma rays)
What EM waves are harmful enough to damage the human body? How?
- UV can cause skin to age prematurely and increase risk of skin cancer
- X and gamma are ionising radiation: cells that absorb them can have no change, mutate (leading to cancer) and die (burns, sickness, death)
What is a real image?
opposite side of lens to objects and can be projected on to screen
What is a virtual image?
same side as the object, can only be seen through the lens
Describe the difference between concave and convex lenses
Convex
- wider in middle
- rays converge
Concave
- wider at edges than middle
- diverging rays
- rays appear to have come from same principal focus on same side of lens as the originated (track diverging rays back behind lens)
What is visible light?
em waves detectable by human eye
What is reflection from a smooth surface in a single direction called?
speculate reflection
What is scattered reflection from a rough surface called?
diffuse reflection
Define:
transparent
translucent
opaque
transparent - transmits light coherently
translucent - transmit light but scattered rays
opaque - reflect or absorb all light so no light passes through
Why do objects appear a certain colour?
- reflects light of that particular wavelength
- absorbing all other wavelength
Why do objects appear white?
reflecting all rays equally
Why do objects appear black?
All wavelengths absorbed
How do colour filters work?
- absorb some wavelengths and not others
- transmitted wavelengths control what colour the filter allows the pass through
they do not mix colours, just absorb and transmit
When a filter is the same colour as the object, what happens?
the object will appear it’s true colour
What will happen if an object is a different colour to the filter?
- the object will appear black
All bodies ___________ and ___________ infrared radiation
emit, absorb
What effect does increasing temperature have on infrared emission?
- The hotter the body, the fast it emits infrared radiation
- intensify if shorter wavelengths increase faster
- goes from red to white
Define a perfect black body
- absorbs all infrared incident on it
- does not reflect or transmit any
- good absorber = good emitter, so perfect black bodies are best possible emitters as well as absorbers
What does the temperature of a body depend on?
- rate of emitting radiation
- wavelength of radiation it emits
Explain how the term pasture if the Earth is determined by emitted and absorbed radiation
- ground on a sunny day increases in temperature
- because it absorbs radiation fast than it emits
- warmer the ground gets the faster it emits radiation
- constant temperature: emission = absorb
What does the temperature of the earth depend on?
- how much energy received from sun
- how much energy is reflected back in to space
- how much energy emitted in to space
