Waves

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what are mechanical waves?
waves that can only travel through a medium
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what are electromagnetic waves?
waves that can travel through a medium AND a vacuum
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what are transverse waves?
waves whose oscillations travel perpendicular to the direction of energy transfer
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what are longitidinal waves?
waves whose oscillations travel parallel to the direction of energy transfer
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what type of waves are sound waves?
mechanical and longitudinal
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what type of waves are light waves?
electromagnetic and transverse
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what is the amplitude of a transverse wave?
the maximum displacement of a point on the wave from its equilibrium
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what is the wavelength of a wave?
the distance from a point on the wave to the equivilant point on the adjacent wave
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the bigger the wave...
the more energy the wave carries
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what is the frequency of a wave?
the number of waves passing a fixed point every second
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what is the period of a wave?
the time taken from each wave to pass a fixed point
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what is the formula involving frequency and the period?
frequency(Hz) = 1 / period(s)
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what is wavespeed?
the distance travelled by each wave every second through a medium
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what is the formula for wavespeed?
wavespeed(m/s) = frequency(Hz) x wavelength(m)
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which formula do you use to calculate the speed of sound in air?
speed(m/s) = distance(m) / time(s)
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what formula shows the relationship between wavefronts at a non-zero angle to a barrier?
incident wavefront = reflected wavefront
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what is refraction?
the change of the direction in which waves are travelling when they cross a boundary
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how can you show refraction in a ripple tank?
when water waves cross a boundary between deep and shallow water, plane waves change direction as they cross the boundary
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why are refracted waves slower after they cross a boundary?
refracted wavefronts are closer together and are at a smaller angle to the boundary than the incident wavefronts, so their wavelengths are longer
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what happens when waves are absorbed by a substance?
the substance would gain heat because it would gain energy from the waves
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what happens to the amplitude of waves as they travel through a substance?
the amplitude decreases because the substance absorbs some of the wave`s energy
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what is the audible human range?
20Hz-20000Hz
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how does echo sounding work?
pulses of high-frequency sound waves from a transmitter are reflected at the sea bed and detected by the ship`s receiver. So, the depth of the sea bed is 1/2vt (the waves go to the sea bed and back)
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what is ultrasound used for?
pre-natal scans, organ imaging, destruction of kidney stones
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each ultrasound wave pulse from the transducer...
is partially reflected from the different tissue boundaries in its path and returns to the transducer as a sequence of ultrasound waves reflected by tissue boundaries (they arrive back at different times)
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what are the advantages of ultrasound over x-rays?
the waves are reflected at boundaries so you can scan different types of tissue, the radiation is non-ionising and therefore harmless
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how is ultrasound used in industrial imaging?
flaws in metal castings can be detected (e.g. an internal crack will partly reflect ultrasound waves from this boundary which can be displayed on a oscilloscope screen)
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what is the formula to calculate distance travelled by ultrasound waves in the body?
distance travelled = speed of ultrasound waves in body tissue x time taken
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what is the formula used to calculate the depth of a boundary in the body
depth of boundary below the surface = 1/2 x speed of ultrasound waves x time taken
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what is the structure of the earth?
crust, mantle, outer core, inner core
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what is the focus of an earthquake?
the point where an earthquake originates from
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what is the epicentre of an earthquake?
the nearest point on the surface to the focus
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what are p-waves?
primary waves: longitudinal waves which last about one minute, push or pull on a material as they move through the earth, fastest
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what are s-waves?
secondary waves: transverse waves, shake the material in the earth from side to side, slower than p-waves
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what are l-waves?
long waves: longitudinal and transverse waves, most violent, cause movements on the surface up, down, backwards and forwards, slowest, only occur in the crust
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where do p-waves refract and what does this do to their speed?
refract at the boundary between the mantle and outer core, this slows the waves
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can s-waves travel through the outer core
no because they are transverse and the outer core is liquid
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what are the 7 electromagnetic waves?
radio, micro, infrared, visible light, UV, x-rays, gamma
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at what speed do em waves travel through a vacuum?
300 million m/s
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the shorter the wavelength of a wave...
the higher the frequency and the greater the energy the wave transfers
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what are the colours in the visible light spectrum?
red, orange, yellow, green, blue, indigo, violet
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the hotter an object is...
the more infrared radiation it emits
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what can infrared radiation do to your cells?
when it`s absorbed by your skin, it can damage, burn or kill skin cells because the cells heat up
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why do optical fibres use infrared radiation instead of visible light?
infrared radiation is absorbed less than visible light in the glass fibres
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what are other uses of infrared radiation?
remote controls for tvs, used in medicine to detect infrared radiation emitted on the body surface (unhealthy tissue), infrared cameras, electric heaters
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do microwaves have a shorter length than radio waves?
yes
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what are the uses of microwaves
communications (satellite tv because they can pass through the atmosphere), microwave ovens (microwaves can penetrate into food and are absorbed by water molecules)
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what is the range of frequencies for radio waves?
300,000Hz - 3000 million Hz
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what are radio waves used for?
to carry radio, tv and mobile phone signals
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why can radio waves be hazardous
they penetrate people`s bodies and can heat the internal parts of the body
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why could mobile phones be dangerous, especially to children?
a mobile phone sends out a radio signal when your use it, if the phone is very close to your brain, scientists think the radiation might affect the brain. children have thinner skulls than adults, so their brains could be more affected.
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what are optical fibres?
very thin glass fibres used to transmit signals carried by light or infrared information
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why do optical fibres carry much more information compared to radio and micro waves?
light has a much shorter wavelength than radio waves, so can carry more pulses of waves
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why are uv waves harmful?
they carry a lot of energy so can cause blindness and burn and damage skin, perhaps resulting in skin cancer
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how are x-rays and gamma rays similar?
short, em waves which carry lots of energy
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how do x-rays and gamma rays differ?
x-rays are produced by electrons moving at high speeds stopping, gamma rays are produced by radioactive substances, gamma rays have a shorter wavelength
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what are gamma rays used for?
kills bacteria such as salmonella in foods, sterilises instruments in hospitals, destroys cancer cells
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what is ionisation and why is it dangerous?
when high-energy waves knock electrons out of atoms in a substance and the atoms become charged. if ionisation happens to a living cell, it can damage, kill, or cause mutations to a cell.
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what precautions do people exposed to x- or gamma rays take?
they must wear a film badge to show if the wearer is over-exposed or not, they have to leave the room when taking x-rays and wear a lead apron
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do x-rays pass through soft tissue?
yes
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what is the law of reflection?
i=r
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what is specular reflection?
reflection froma smooth surface where parallel light rays are reflected in a single direction
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what is diffuse reflection?
reflection from a rough surface where light is scattered in different directions
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what is the formula to find the constant value?
constant value = Sin(i) / Sin(r)
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what happens when light enter a more-dense medium?
it`s refracted toward the normal
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what are the primary colours?
red, blue, green
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what are the secondary colours?
cyan, yellow, magenta
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what are transparent objects?
objects that transmit all the indident light that enters the object
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what are translucent objects?
objects that let light pass through them, but light is scattered or refracted
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what is an opaque object?
an object that absorbs the light that reaches it
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what does a convex lens do?
makes parallel rays converge to a focus
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what are convex lenses used for?
magnifying glass, cameras
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what is a concave lens?
a lens that makes parallel rays diverge
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what is the focal length?
the distance from the centre of the lens to the principle focus
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what are the properties of an image created by a convex lens?
real, inverted, smaller than the object
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what is the formula for the magnification produced by a lens?
magnification = image height / object height
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what are the properties of an image created by a convex magnifying glass?
virtual, upright, larger than the object
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what are the properties of an image created by a concave lens?
virtual, upright, smaller than the object
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what is the formula for the power of a lens?
power = 1 / focal distance
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what vision defect do convex lenses correct?
hyperopia
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Other cards in this set

Card 2

Front

what are electromagnetic waves?

Back

waves that can travel through a medium AND a vacuum

Card 3

Front

what are transverse waves?

Back

Preview of the front of card 3

Card 4

Front

what are longitidinal waves?

Back

Preview of the front of card 4

Card 5

Front

what type of waves are sound waves?

Back

Preview of the front of card 5
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