p6 Flashcards
what is a wave?
a wave is a disturbance that transfers energy without transferring matter
what is an oscillation?
object repeatedly moving back and forth in a regular rhythm
what are transverse waves?
oscillations are perpendicular to the direction of energy transfer (or the direction of wave travel)
what are longitudinal waves?
oscillations are parallel to the direction of energy transfer (or wave travel)
what is the wavelength of a wave?
the distance from one point on a wave to the corresponding point on an adjacent wave
what is amplitude of a wave?
the maximum displacement of a point on a wave from the resting position
what is the frequency of a wave?
the number of waves passing a point in one second. measured in Hz
what is the time period of a wave?
time for one wave to pass a point. measured in seconds (s)
what is the equation that links frequency and time period
time period = 1/ frequency
what is the equation that links frequency, wavelength and wave speed
wave speed = frequency * wavelength
what four things can happen to a wave when it meets a boundary?
- absorption
- reflection
- transmission
- refraction
what is reflection
occurs when a wave or particle bounces from the surface of an object or from the boundary between two materials
what is the normal in waves?
an imaginary line 90° to the surface/ boundary and acts at the point of interaction
what is the law of reflection?
the angle of incidence is equal to the angle of reflection (only for specular reflection)
what is refraction?
refraction is the change in the direction of a wave as it passes from one material into another across a boundary due to a change in wave speed
what happens when a wave travels from a less dense to a more dense medium? e.g from air to glass
TAG - towards air glass
wave refracts towards the normal
what happens when a wave travels from a more dense medium into a less dense medium? e.g from glass to air
AGA - away glass air
the wave refracts away from the normal
what is a lens?
a lens is a transparent block that has been shaped to retract light to form an image
what is the principle focus of a lens?
the point at which the light rays meet
what is the focal length of a lens?
the distance between the centre of a lens and the principal focus
what are the three steps for constructing lens ray diagrams?
- draw a ray parallel to the principal axis from the top of the object to the lens
- continue from the end of the parallel ray, drawing a ray that passes through the principal focus
- draw a ray from the top of the object through the centre of the lens
what are the three ways to describe images formed by lenses?
- upright or inverted
- magnified or diminished
- real or virtual
what are five properties or EM waves?
- all transverse waves
- travel at the speed of light (3x10^8)
- can travel through a vacuum
- follow the wave speed equation
- can be reflected or refracted
state the types of wave in order of decreasing wavelength
radio
micro wave
infrared
visible
ultraviolet
x ray
gamma ray
what happens when an electron absorbs an EM wave?
it moves away from the nucleus by jumping up to a higher energy level
what happens when an electron emits an EM wave?
it moves closer to the nucleus by falling to a lower energy level
what are the uses of radio waves?
communication - radios and tvs send and receive radio waves
what are 3 the uses of microwaves?
- satellite communication: microwaves are received and sent by satellites
- cooking: microwaves are absorbed by water molecules. water in food is heated so food is also heated
- mobile phone communication: mobile phones send and receive signals as microwaves
what are the two uses of infrared?
- thermal imaging: all objects emit and absorb infrared waves
- remote controls send IR waves to communicate with a tv
what is the use of visible light?
communication - super fast internet signals are sent as visible light along optical fibres
what are the three uses of ultraviolet?
- tanning
- detecting forged banknotes/ passports
- kill microbes/ sterilise surgical equipment
what are the two uses of x rays?
- medical imaging to detect broken bones and dental problems
- security imaging at airports to scan for dangerous items
what are the two uses of gamma rays?
- in radio therapy high doses of gamma rays are used to kill cancer cells
- sterilisation of food and surgical instruments
what are the dangers of radio waves?
no effect
what are the dangers of micro waves?
very minor heating effect
what are the dangers of infrared?
infrared can cause skin burns
what are the dangers of visible light?
very bright light can damage your eyes (even blindness)
what are the dangers of ultraviolet?
- premature skin aging
- eye damage
- ionising radiation so can cause gene mutation or cell death leading to cancer
what are the dangers of x rays and gamma rays?
ionising radiation so can cause gene mutation and cell death leading to cancer
how are radio waves transmitted and received?
- electrons in the transmitter oscillate (a.c) to produce radio waves
- radio waves are absorbed by electrons in the receiver (aerial)
- this induces an alternating current in the aerial circuit
- alternating current has the same frequency as the radio waves
how does an object hotter than its surroundings reach thermal equilibrium?
- an object hotter than its surroundings will emit IR at a greater rate than it will absorb it
- therefore, temperature of the object will decrease
- eventually, the temperature of the object will match its surroundings
- so the rate of IR emission is equal to the rate of IR absorption
what colour is the best emitter and absorber or IR ?
black
what colour is the worst emitter and absorber of IR?
white
what type of surface is good at absorbing and emitting IR radiation?
dull surfaces
what type of surfaces are the worst reflectors of IR?
dull surfaces
what type of surface is poor at absorbing and emitting IR?
shiny surface
what type of surface is good at reflecting IR?
shiny
what is white light made up of?
equal combination of all the colours
if all wavelengths are absorbed what colour will an object appear?
matte black
what are the primary colours?
- blue
- red
- green
what are the secondary colours?
- magenta
- yellow
- cyan
what colour does a red object appear if cyan light is incident upon it?
black because cyan light is a mixture of blue and green and red has none of these
what colour will a magenta object appear in cyan light? explain
- cyan light is a mixture of blue and green
- the magenta objext will reflect only the blue light making the object appear blue to the observer
- the green light is absorbed by the object
what type of wave are sound waves?
longitudinal
how are sound waves produced?
when an object vibrates
why can’t sound waves travel through a vacuum?
there are no particles to pass on vibrations
what medium do sound waves travel fastest in? why?
solids
the particles are more tightly packed so it is easier for vibrations to be passed on
how does normal human hearing range work?
the conversion of sound waves to vibrations of solid structures within the ear only works over a limited frequency range:
20Hz to 20,000Hz
what are three uses of ultrasound?
- echolocation/ sonar
- foetal ultrasound scanning
- detecting cracks or faults
what is echolocation ?
method used to detect objects by producing an ultrasound and listening for its echo
explain how echolocation is used to measure the distance to the bottom of the sea?
- ultrasound waves are emitted which have a frequency above 20,000 Hz
- when the sound waves meet a different medium (sea floor) they are partially reflected
- the time between the emission or the wave and the detection of the reflected wave is measured
- sinfe the speed of the wave is known, distance can be calculated using distance = speed * (time/2)
describe how x rays are able to produce an image of bones?
- x rays are absorbed by bone
- x rays are transmitted by soft tissue
- transmitted x rays are detected
what type of waves are seismic P waves?
seismic (primary) waves are longitudinal
what type of waves are seismic s waves?
seismic secondary waves are transverse
what instrument is used to detect seismic waves?
seismometer
compare seismic s waves and p waves
- s waves are slower than p waves
- s waves can only travel through solids whereas p waves can travel through solids and liquids
- s waves are transverse and p waves are longitudinal
what is the state of each layer of the earth?
crust: solid
mantle: solid
outer core: liquid
inner core: solid
when investigating the refraction of light with a ray box, why should the ray of light from the ray box be as narrow as possible? (2)
it is harder to judge where the centre of a wider ray is
causing larger uncertainty in measurements
giving less accurate results
what property of a light wave changes when it’s refracted?
velocity
describe why a blue object appears black when light is passed through a red filter (3)
only red is transmitted by the filter
red is absorbed by the blue object
- so no livht is reflected by the blue object
when investigating the angles of refraction, why is having a protractor drawn on the paper better? (2)
you do not have to move the mirror to measure angles
so more likely to record the correct angle of incidence and angle of reflection
what is the name given to reflection off a smooth surface?
specular reflection
explain why the study of seismic waves provides evidence for the structure of the earths core (2)
- s waves do not travel through liquid
- so s waves do not travel through outer core
when investigating reflection, how would the hypothesis be proved?
if within experimental accuracy, the angle of incidence and the angle of reflection are the same.
instead of using a mirror, what is used to investigate diffuse reflection?
an irregular reflecting surface
