topic 6 - Waves Flashcards
what are the two types of waves?
- longitudinal waves
- transverse waves
what is a transverse wave?
a wave for which the oscillations are perpendicular to the direction of energy transfer
what is a longitudinal wave?
a wave for which the oscillations are parallel to the direction of energy transfer
what are two examples of transverse waves?
- electromagnetic waves
- seismic s-waves
what are two examples of longitudinal waves?
- sound waves
- seismic p-waves
what are the two parts of a longitudinal wave called?
compressions and rarefactions
what is the frequency of a wave?
the number of waves that pass a given point each second
what is the unit used for frequency?
Hertz, Hz
what does a wave transfer?
energy
what word is used to describe when a wave bounces off a surface?
reflection
when does reflection occur?
when a wave hits a boundary between two media and does not pass through, but instead stays in the original medium
what is the law of reflection?
the angle of incidence = the angle of reflection
what are echoes an example of?
sound waves being reflected off a surface
what surfaces are the most reflective?
the smoother the surface, the stronger the reflected wave
what surfaces are the least reflective?
- rough surfaces are the least reflective
- this is because the light scatters in all directions
what do opaque surfaces reflect?
- opaque surfaces will reflect what is not absorbed by the material
- the electrons will absorb the light energy and then reemit it as a reflected wave
when does transmission occur?
when a wave passes through a substance
how does the transparency of a material affect light waves?
the more transparent the material, the more light will pass through
what must be occur for transmission to happen?
for the process to count as transmission, the wave must pass through the material and emerge from the other side
when does absorption occur?
when energy is transferred from the wave into the particles of substance
How is light absorbed?
- light will be absorbed if the frequency of light matches the energy levels of the electrons
- the light will be absorbed, and then reemitted over time as heat
what does it mean when an object appears red?
- only red light has been reflected
- all the other frequencies of visible light have been absorbed
what are sound waves?
- vibrations of air molecules
- can travel through solids causing vibrations in the solid
what happens when a sound wave hits a solid?
- the variations in pressure cause the surface of the solid to vibrate in sync with the sound wave
What do sound waves consist of?
- compressions - regions of higher density
- rarefactions - regions of lower density
what happens when sound moves from a denser medium to a less dense medium?
- the wavelength of the sound waves increases
- the frequency of the sound wave stays the same
- the velocity of the sound wave increases
what happens when sound moves from a less dense medium to a denser medium?
- the wavelength of the sound wave decreases
- the frequency of the sound wave stays the same
- the velocity of the sound wave decreases
what is an angle of incidence?
the angle between the incident ray and the normal
what is the relationship between the angle of incidence and the angle of reflection?
they are equal
what is the frequency range of human hearing?
20Hz - 20KHZ
what are ultrasound waves?
sound that vibrates at frequencies above 20,000Hz
what are some uses for ultrasound waves?
- prenatal scanning
- industrial imaging
- sonar
describe how sound waves travel through the human ear
- the sound wave travels down the auditory canal towards the eardrum
- the pressure variations created by the sound wave exert a varying force on the eardrum causing it to vibrate
- the vibration pattern of the sound waves creates the same pattern of vibration in the eardrum
- the eardrum vibration is transferred to the three small bones (hammer, anvil, stirrup)
- the vibrations are transferred to the inner ear where nerve cells detect the sound and send a message to the brain giving the sensation of sound
what are the uses of sound waves?
echo sounding - used by shipping to detect the ocean floor
ultrasound - used to look inside the human body
ultrasound crack detection- to find cracks in rail tracks
reflection seismology - to detect oil and gas underground
seismic activity - can be used to investigate the structure of the earth
describe the prenatal scanning method
- ultrasound waves are produced in the transducer
- some of the ultrasound waves are reflected each time it meets a different material such as bone, muscle or fluid
- the reflected wave is detected by the transducer each time taken is measured
- using the time taken, the distance to different parts of the fetus is calculated and image is built up
describe the prenatal scanning method.
- ultrasound waves are produced in the transducer
- some of the ultrasound waves are reflected each time it meets a different material such as bone, muscle or fluid
- the reflected wave is detected by the transducer each time taken is measured
- using the time taken, the distance to different parts of the fetus is calculated and image is built up
what are the advantages of ultrasound waves?
- the ultrasound reflects all types of tissue so can be used to scan many organs or tissues
- x-rays used for bones are ionising. Ultrasound is non-ionising
how is ultrasound used by ships to determine the distance to shoals of fish?
- ultrasound signal is produced by the ship
- ultrasound signal reflected by the fish
- reflected signal detected by the ship
- time taken between emission and detection measured
- then use distance = velocity x time
what natural event causes seismic waves to be produced?
- earthquakes
what types of waves do seismic waves produce?
P- waves
S-waves
what is the difference between the mediums that P-waves and S-waves can travel through?
- P-waves travel through both solids and liquids
- S-waves are transverse, seismic waves, they only travel through solids
what is the nearest point on the Earth’s surface called?
epicentre
what are shadow zones?
areas that are unable to detect seismic waves
What happens to P and S waves as they travel through the mantle?
- P and S waves bend as they travel through the mantle as their speed changes with depth
what does the discovery of shadow zones suggest about the outer core?
the outer core is liquid, as S-waves are transverse waves so they cannot pass through
why do both waves change direction as they go deeper into the earth?
due to the change in medium, they change speed and refract
what is used by lenses to form an image?
refraction
what wave is used by lenses to form an image?
refraction
how does a convex lens form an image?
parallel rays of light are refracted and brought together at a point known as the principal focus
what is meant by the focal length of a lens?
the distance from the lens to the principal focus
what is the difference between the image produced by a convex and a concave lens?
- convex lenses can produce real or virtual images
- concave lenses can only produce virtual images
why does magnification not have a unit?
- it is the ratio between image height and object height
- ratios do not require units
what determines the colour of visible light waves?
the wavelength and frequency of the light waves
what colour of visible light has the highest frequency?
blue
what colour of visible light has the largest wavelength?
red
what is meant by the term “specular reflection”?
reflection from a smooth surface in a single direction
what happens to the wavelengths of light that arent reflected by an opaque object?
any wavelengths that aren’t reflected are absorbed by the object
what colour does an object appear if all wavelengths are reflected in equal amounts?
white
what colour does an object appear if all wavelengths are absorbed?
black
what do all objects emit and absorb?
infrared radiation
what happens to the infrared radiation emitted by an object as temperature increases?
- the hotter the object, the more infrared radiation it will emit
what is a perfect black body?
- an object that absorbs all of the radiation incidents on it
- a black body does not reflect or transmit any radiation
- since a good absorber is also a good emitter, a perfect black body would be the best possible emitter
what is a perfect black body?
- an object that absorbs all of the radiation incidents on it
- a black body does not reflect or transmit any radiation
- since a good absorber is also a good emitter, a perfect black body would be the best possible emitter
what does the temperature of the Earth depend on?
- the rates of absorption - emission of radiation
- reflection of radiation into space
how much radiation does a perfect black body reflect or transmit?
none
what can be said about the rates of emission and absorption for a body at constant temperature?
- the body is absorbing and emitting radiation at the same rate
how do emergency blankets keep a trauma victim warm?
- rescue teams use light-coloured, shiny emergency blankets to keep accident survivors warm
- a light, shiny outer surface emits a lot less radiation than a dark, matt surface
- this keeps the patient warm, as less infrared radiation is emitted than if an ordinary blanket had been used
what is the amplitude of a wave?
- the maximum displacement of a point on a wave away from its undisturbed position
