waves Flashcards
Name the two types of waves
- Transverse
- Longitudinal
Define transverse waves
- The direction of oscillation is perpendicular to the direction of energy transfer
Name examples of transverse waves
- Electromagnetic waves like light and microwaves, ripples on a water surface
Define longitudinal waves
- The direction of oscillation is parallel to the direction of energy transfer
Name examples of longitudinal waves
- Sound waves travelling through air
What is the difference between transverse and longitudinal waves (medium)
- All longitudinal waves require a medium to travel through (gas, liquid, solid) whereas some transverse waves can travel through a vacuum e.g., electromagnetic waves
What is the purpose of all waves?
- They transfer energy from one place to another
e.g., ripples transfer kinetic energy, sound waves transfer sound energy
Describe evidence that for ripples on a water surface, it is the wave and not the water itself that travels
- If you place a floating duck on a water wave (transverse) the duck will bob up and down but will not move from side to side
Describe the evidence that for sound waves in air, it is the wave and not the air itself that travels
- If you use a slinky to model a longitudinal wave and mark a fixed point on the slinky, it will move side to side but does not travel through the medium
What is the top of the wave called?
- The peak or the crest
What is the bottom of the wave called?
- The trough
Define the amplitude of a wave
- The maximum displacement of a point on a wave away from its undisturbed position
Define the wavelength of a wave
- The distance from a point on one wave to the equivalent point on the adjacent wave
Define the frequency of a wave
- The number of waves passing a point each second
Define the wave speed of a wave
- The speed at which the energy is transferred (or the wave moves) through the medium
Define the period of a wave
- The time taken for one wave to pass a point
How can you measure the speed of sound waves in the air?
1) Person A has cymbals, person B has timer
2) Make them stand 500m apart
3) Person A crashes cymbals together; person B starts stopwatch when they see person A crash cymbals and stops stopwatch when they hear crash of cymbals
4) Calculate speed of sound waves by doing S=D/t
How can you use an oscilloscope to measure speed of sound?
- Set up the scope sot he detected waves at each microphone are shown as separate waves
- Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display but have moved exactly one wavelength apart
- Measure distance between phones to find one wavelength
- Use formula for wave speed
What are the problems with the experiment for measuring speed of sound waves in air? How to resolve them?
- Different people have different reaction times, giving way for inaccuracies
to overcome this - We can use a large number of observers with timers and calculating a mean
- It is only a very short space of time between seeing cymbals crash and hearing them, making it very difficult to press stopwatch at correct times
- Increasing distance between the people can reduce this problem
What happens to waves between two different materials (at the boundary)?
- At the boundary, they can be reflected, absorbed or transmitted
What happens when a wave is absorbed?
- Transfers energy to the material’s energy stores
What happens when a wave is transmitted?
- Waves carry on travelling through the new material
- Often leads to refraction
What does the activity of a wavelength depend on (absorb transmit reflect)?
- Properties of the materials involed
Describe how you would draw a simple ray diagram for reflection
- Angle of incidence = angle of reflection
- Draw incoming ray, hitting the boundary and normal line (perpendicular
- Draw reflected ray at the same angle
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What can sound waves travel through?
- Solids, causing vibrations in the solid
How are the limits of human hearing restricted?
- Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound
- The conversion of sound waves to vibrations of solids works over a limited frequency range
- Thus restricting the limits of human hearing
What is the range of normal human hearing?
- 20Hz to 20kHz
- Frequencies outside this range do not cause the ear drum to vibrate
How do microphones detect sound waves?
- The sound waves cause the microphone to vibrate
- Microphones transfer these vibrations into an electrical signal by detecting the sound waves’ frequency and amplitude as the waves hit the paper cone
- Causing it to vibrate forwards and backwards
What do sound waves move faster in and why?
- Sound waves move faster in solids than in gases
- They are longitudinal mechanical waves rather than being electromagnetic, so because particles are closer together in solids
- Vibrations can be passed on more easily between them
What happens when waves move from one medium to another?
- Their speed can change; when wave speed changes as waves pass from one medium to another, wavelength must also change - that is because the frequency never changes (bc that would mean we’re not abiding by the law of conservation of energy)
therefore increasing wave speed would increase wavelength, and decreasing wave speed would decrease wavelength
What does a cathode ray oscilloscope do and what’s an issue with using one?
- It allows us to see the features of sound waves; the only issue is that it represents sound waves as transverse waves which is incorrect
What are the properties of a cathode ray oscilloscope wave?
- Frequency controls pitch; high frequency means high pitch and vice versa
- Amplitude controls volume; high amplitude means loud volume and vice versa
Define echo
- A reflected sound wave
What is ultrasound?
- Sound waves with a frequency higher than the upper limit of hearing for humans (i.e., >20kHz)
What happens to ultrasound waves at a boundary?
- They are partially reflected when they meet a boundary between two different media (with different densities)
How can you determine how far away a boundary is?
- Use the time taken for the reflections to reach a detector, and multiply it by the speed of the ultrasound wave (which is shown on the device)
- This is the distance = speed x time equation
What are ultrasound waves used for?
- Medical imaging; e.g., internal organs, prenatal scanning
- Industrial imaging; e.g., detecting hidden defects like cracks or air bubbles
What are the condition for using ultrasound waves for producing images of internal organs
- The organ cannot be surrounded by bone, otherwise it would absorb the ultrasound wave and wouldn’t be detected by the scanner
What are the pros of ultrasound waves over x-rays?
- Ultrasound is much safer than x-rays because it is non-ionising unlike x-rays, therefore it doesn’t increase the risk of mutations and cancer
- Ultrasound can distinguish between two different types of soft tissue, unlike x-rays which would just penetrate through both
Why can ultrasound be used for industrial imaging?
- Because there is a difference in density between hidden defects like air bubbles and the rest of the material, so partial reflection takes place at the boundary
State of the layers of the Earth
- Mantle - solid
- Outer core - liquid
- Inner core - solid
What did the study of seismic waves aid?
- They provided new evidence that led to discoveries about the structure of the Earth which is not directly observable
How are seismic waves produced?
- They’re produced by earthquakes; when an earthquake occurs due to a sudden movement between tectonic plates in the earth’s crust, seismic waves are emitted, which carry energy away from the earthquake
What happens after seismic waves are emitted?
- They can pass through the earth and be detected by seismometers; the patterns of these waves give us the information about the internal structure of the earth
Name the types of seismic waves
- P-waves (primary waves)
- S-waves (secondary waves)
What type of waves are the seismic waves?
- P-waves are longitudinal seismic waves
- S-waves are transverse seismic waves
What can the seismic waves pass through?
- P-waves can travel at different speeds through both solids and liquids
- S-waves can only travel through solids
- S- waves Solids (way to remember)
What seismic wave travels faster?
- P waves travel faster than s waves
Define echo sounding
- The use of high frequency sound waves to detect objects in deep water and measure water depth
Define electromagnetic waves
- Transverse waves that transfer energy from the source of the waves to an absorber
What do electromagnetic waves form?
- They form a continuous spectrum
How do electromagnetic waves travel?
- They travel at the same velocity through a vacuum (space) or air
How are electromagnetic waves grouped?
- In terms of their wavelength and their frequency
Order of electromagnetic waves
- Red - radio waves
- Men - microwaves
- Invaded - infrared
- Venus - visible light
- Using - ultraviolet
- X-Ray - x-ray
- Guns - gamma rays
List the electromagnetic wave spectrum from short to long wavelength
- Gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, radio waves
List the electromagnetic wave spectrum from low to high frequency
- Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
What electromagnetic wave(s) do our eyes detect?
- Our eyes only detect visible light and so detect a limited range of electromagnetic waves
What are radio waves produced by?
- Oscillations in electrical circuits
What happens when radio waves are absorbed?
- They may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical current
What do gamma rays originate from?
- Changes in the nucleus of an atom
What do changes in atoms and the nuclei of atoms result in?
- Electromagnetic waves being generated or absorbed over a wife frequency range
What electromagnetic waves can have hazardous effects?
- Ultraviolet waves, x-rays and gamma rays on human body tissue
What do the hazardous effects from electromagnetic waves depend on?
- The type of radiation and the size of the dose
Define radiation dose
- A measure of the risk of harm resulting from an exposure of the body to the radiation
What is the unit of radiation + conversion?
- Sieverts (Sv)
- 1000 millisieverts (mSv) = 1 sievert (Sv)
What are the effects of ultraviolet waves on the body?
- They can cause skin to age prematurely and increase the risk of skin cancer
What are the effects of x-rays and gamma rays on the body?
- They are ionising radiation that can cause the mutation of genes and cancer
What are EM wavse made up of?
- oscillating electric and magnetic fields
- Alternating currents are made up of oscillating charges, producing oscillating electric and magnetic fields
- Frequency of waves produced equal to frequency of A.c
What are the practical applications of radio waves and how is it suitable?
- Television and radio
- They can easily pass through air
- Alternating currents in an electric circuit, object which charges oscillate to create RW is a transmitted
- When transmitted RW reach a receiver, radio waves are absorbed
- Energy transferred by waves is energy transferred to electrons in the material of the receiver
- Energy causes electrons to oscillate and if receiver is part of a complete circuit it generates a.c.
- current has same frequency as RW
- Long RW can be transmitted far because they bend around curved surfaces on the earth - can receive signals even if not in line of sight
- Short wave RW are reflected into the ion sphere
What are the practical applications of microwaves and how is it suitable?
- Satellite communications, cooking food
- Microwaves are absorbed by water molecules in the food; the energy carried by the waves turns into thermal energy in the food
What are the practical applications of infrared waves and how is it suitable?
- Electrical heaters, cooking food, infrared cameras
- Camera detects IR radiation and turns it into an electrical signal which is displayed as a picture
- The temp of food increases when it absorbs IR radiation
- Heaters emit IR which is absorbed by objects into room, transferred to thermal energy stores
What are the practical applications of visible light waves and how is it suitable?
- Fibre optic communications
- Work because of reflection, light rays bounced back and forth until reach end of fibre
- Light not easily absorbed or scattered
What are the practical applications of ultraviolet waves and how is it suitable?
- Energy efficient lamps, sun tanning
- Fluorescence - UV is absorbed and visible light is emitted
- Under UV light ink glows, otherwise invisible
What are the practical applications of x-rays and gamma rays and how is it suitable?
- Medical imaging and treatments
- Xray easily pass through flesh but not denser material
How does a lens form an image?
- By refracting light
Describe how a convex lens works
- Convex lenses bulges outwards
- Parallel rays of light are brought to a focus a the principal focus (converge)
- Principal focus of convex lens is where rays hitting the lens parallel to the axis all met
Describe how a concave lens works
- Caves inwards
- Rays of light to diverge (spread out
- Principal focus of a concave lens is the point where rays hitting the lens parallel to the axis appear to all com from
Define the axis of a lens
- Line passing through the middle of a lens
Define the focal length
- The distance from the lens to the principal focus
What do ray diagrams show?
- The formation of images by convex and concave lens
What are the three rules for refraction in a convex lens?
- An incident ray parallel to the axis refracts through the lens and passes through the principal focus ont he other side
- An incident ray passing through the PF refracts thruogh the lens and travels parallel to the axis
- An incident ray passing through teh center of the lens carries on in the same direction
What are the three rules for refration in a concave lens?
- An incident ray parallel to the axis refrats through the lens and travels in a line with the principal focus
- An incident ray passing thruogh the lens towards the PF refracts through the lens and travels parallel to the axis
- An incident ray passing through teh centre of the lens carries on in the same direction
What images do convex lens produced?
- Can either be real or virtual
What images do concave lens produce?
- Always virtual
Define a real image
- Where the light from an object comes together to form an image on the screen
Define a virtual image
- When the rays diverge so the light from the object appears to be coming from a different place
e.g. mirror, or magnifying lens
How would you describe an image?
- How big it is compared to the object
- Upright or inverted
- Real or virtual
Define specular reflection
- Reflection from a smooth surface in a single direction
- You get a clear reflection
Define diffuse reflection
- Reflection from a rough surface causes scattering in different directions
- This is because the normal is different for each incoming ray, meaning the angle of incidence is different
- You do not get a clear reflection of objects
Describe refraction
- When a wave crosses a boundary between materials at an angle it changes direction and is refracted
What does refraction depend on?
- How much he wave speeds up or slows down or he density of the materials
- The higher the density the slower a wave travels
What happens if a wave slows down/ speeds up when it crosses a boundary?
- Slows down = bend towards normal
- Speeds up = bends away from normal
What happens when a wave is refracted?
- Wavelength changes, frequency stays the same
What happens if a light hits the boundary face on compared to if it meets a different medium?
- Face on, carries on in the same direction, wave fronts closer to show change in wavelength (and velocity)
- Different medium at an angle means wave changes direction, its been refracted
Define optical density
- Measure of how quickly light can travel through it
- Higher the optical density the slower light waves travel
How do colour filters work?
- By absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour)
How can you construct a ray diagram to show refraction?
- Draw boundary and normal line
- Draw incident ray, and angle of incidence
- Draw refracted ray on the other side of the boundary
- If second material is optically denser, bend towards
- The angle between the refracted ray and normal is smaller
- If second materially less optically dense, angle refraction is larger
How is the colour of an opaque object determined?
- It’s determined by which wavelengths of light are more strongly reflected
- Wavelengths that are not reflected are absorbed.
- If all wavelengths are reflected equally the object appears white
- If all wavelengths are absorbed the object appears black
What are colour filters used for
- To filter out different wavelengths of light so that only certain colours are transmitted, rest are absorbed
Define transparent or translucent objects
- Objects that transmit light
What objects absorb infrared radiation and under what conditions?
- All bodies (objects), no matter what temperature, emit and absorb infrared radiation.
- The hotter the body, the more infrared radiation it radiates in a given time
Describe the emitting and absorption of radiation
- An object that is hotter than its surroundings emit more IR than it absorbs and cools down
- An object cooler than its surroundings absorbs more IR than it emits and warms up
- Objects at a constant temp emit IR at the same rate it aborbs
Define a perfect black body
- An object that absorbs all of the radiation incident 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 intensity and distribution of wavelentghs emitted by an object depend on ?
- Object’s temp
- Intensity is power per unit area
- As temp increases, intensity of every wavelength increases
- Intensity increases more rapidly for shorter wavelength than longer
- Causes the peak wavelength to decrease
How are changes in velocity, frequency and wavelength are inter-related in the transmission of sound waves?
- Velocity of sound is directly proportional to the wavelength, thus, if the velocity of sound doubles when it travels from one medium to another, its wavelength also doubles; the frequency of sound depends upon the source of sound, not the medium of propagation so it does not change.
