Unit 3 - Waves Flashcards
Source of waves
Produced by vibrations causing a disturbance which spreads out from the source
What waves transfer
Waves transfer energy from one place to another without transferring matter
Types of waves
- Transverse wave
- Longitudinal wave
Transverse wave
The particles oscillate perpendicular to the direction of propagation of the wave
Longitudinal wave
The particles oscillate parallel to the direction of propagation of the wave
Crest
The peak of the wave
Trough
The lowest point of the wave
Amplitude
The height of the wave
Frequency
The number of complete waves that pass a point each second
Unit of frequency
Hertz (Hz)
Wavelength
The distance between one wave crest and the next (or trough)
Wave speed calculation
Wave speed (m/s) = Frequency (Hz) x wavelength (m)
Relationship with amplitude and energy
If amplitude increases, more energy is transferred per second
Transverse wave examples
- Ripples along the surface of water
- Waves formed by shaken rope
- Visible light and electromagnetic radiation
Longitudinal wave examples
- Waves produced when ends of a stretched spring are moved
- Sound waves- series of compressions and rarefactions
Earthquake waves
- Primary waves - longitudinal - ground is compressed in the same direction as the wave travels
- Secondary waves - transverse - ground rises and falls as wave passes through
Reflection
When a wave ‘bounces’ off a boundary
Refraction
When a wave moves from one medium to another and changes speed and hence direction
Diffraction
When a wave spreads as it moves through a gap or passes and edge
Incident wave
The wave before it reaches a boundary
Reflected wave
The wave after it has hit the boundary and bounced off
Reflection constants
- Wave speed, frequency and wavelength doesn’t change
Increasing effect of diffraction
Gap and wavelength are of similar size
Normal line
Drawn to measure angle of incidence and reflection
Law of reflection
Angle of incidence = Angle of reflection
Virtual image
When rays of not pass through the place an image is seen - hence can’t be projected onto screens
Real image
An image that can be projected onto a screen because the rays of light actually pass through the position of the image
Refractive index
Shows how much the speed of light changes when it moves from a vacuum to a certain material
Refractive index equation
Refractive index (n) = Speed of light in vacuum ÷ Speed of light in a substance
Snell’s law
Relationship with angle of incidence and refraction is constant ration which is refractive index
n = sin i ÷ sin r
Light reflecting off the back surface of a medium
Internal reflection
Total internal reflection
When all of the light leaving a glass block is reflected back inside
Needs for total internal reflection
- Angle of incidence if greater than critical angle
- Wave needs to speed up after it passes across
Critical angle
The largest angle of incidence which allows light to escape the medium
Relationship of critical angle and refractive index
refractive index (n) = 1 ÷ sin c
Use of total internal reflection
Optical fibers - transmis optical pulses over long distances, pulse can be detected since the pulse doesn’t leave the fibre
- Optical fibers - endoscopes
Types of actions of lenses
- Diverging light (spreading it out)
- Converging light (bringing it towards a point)
Converging lens
- Refracts light rays to come together
- If light rays are parallel to each other and to the optical axis, rays will come together to the principal focus
Optical axis
The line which passes through the centre of the lens
Principal focus
The point where the rays of light in a converging lens are brought together
Focal length
The distance between the centre of the lens and the principal focus
Characteristics of an image with a converging lens
- Enlarged or diminished
- Upright or inverted
- real or virtual
Type of image with a converging lens and an object inside the focal length
An upright, magnified, virtual image
Type of image with converging lens and an object twice the focal length
An inverted, diminished, real image
Diverging lens
- Refracts rays of light to spread apart
- if light rays are parallel to each other and optical axis, they will be spread out from the same place - the principal focus of the lens
Relationship of focal length and lens strength
The shorter the focal length, the more powerful the lens
Properties of an image with a diverging sense
- Virtual - rays do not pass through
- Diminished - always is smaller than the original
- Upright - same way up as the original object
Converging lenses in the eye
- Cornea
- Lens
- Both focus light onto the retina
Far point vs. near point
- Far point - most distant point you can focus your eye to
- Near point - closest point you can focus on
Short-sightedness
- Thick lens causes light from distant objects to be focused in front of the retina, far point decreases
Long-sightedness
- Lens isn’t thick enough or eyeball is to short causes light from nearby objects to be focused on a point behind the retina, near point increases
Dispersion
When a ray passes through a medium and splits the white light splits into different components/wavelengths
Seven colors of white light in dispersion in increasing frequency
- Red
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet
Light of only a single frequency
Monochromatic
Electromagnetic waves, wave type
- Transverse waves
Special feature of electromagnetic waves
- Can travel in a vacuum
Electromagnetic waves from shortest to largest
- Gamma rays
- X-ray
- Ultra-violet
- Infrared
- Micro-waves
-Radio waves
Non-ionizing radiation
Type of radiation that does not directly damage cells unless intense
Ionizing radiation
Radiation that can damage cells even at low intensity
Reasons for different wavelengths
Electrons that oscillate at different frequencies
How radio and television broadcasts work
Radio signals are refracted by upper atmosphere and can travel past the curvature of earth
Radio astronomy
Using large radio waves to detect weak radii signals from stars and black holes
Uses of microwaves
- Microwave ovens - cooks food by heating rapidly
- Satellite and phone communication - microwaves can penetrate upper atmosphere, can be used with low power in mobile phone networks
Danger of microwaves
- Heating effect damages living tissue
Uses of infrared radiation
- Remote controls - uses pulses of infrared to be detected on television
- Cooking - heating effect when absorbed is used for cooking
- Thermal imaging and alarms - night vision, identifying energy loss, finding hotspots, medical diagnosis
- Communication - used in fibre optic networks
Dangers of infrared radiation
Heating effect that can bun skin
Visible light
Electromagnetic radiation that can be seen by the eye
Ultraviolet radiation
Produced by the sun and absorbed by the atmosphere
Uses of ultraviolet radiation
- Biological washing powder
- Bleaching paper exposed to UV
- Sterilizes water in waste treatment plants and water supplies - kills microbes
Danger of UV
Damaging to skin and eyes - ca burn skin cells and lead to cancer
X-rays
Short wavelength electromagnetic waves - produce fast-moving electrons
- Also emitted by stars and astronomical objects
Uses of X-rays
- X-ray machines to take photos of bones inside the body since rays go through bones and muscle easily - can be used by doctors
- Security in airports and more - luggages can be scanned for dangerous objects
Danger of X-rays
Can damage cells - especially growing ones
Gamma rays
Produced by the radioactive decay of a nucleus
Uses of gamma rays
- Gamma camera - used to show how healthy organs are if radiation is emitted
- Radiotherapy - kills cancerous cells
- Sterilize medical equipment
Dangers of gamma rays
Damages DNA inside cells which can cause cancer
Two most important types of satellites
- Low Earth Orbit (LEO) satellites - not far above the atmosphere moving quickly across the sky
- Geostationary satellite - far out in an orbit that makes them seem stationary
Low Earth Orbit satellites
- Some used for spying or observing weather
- Part of phone networks or internet
Geostationary satellites
- Positioned 36000km above the Earth’s equator
- Takes exactly one day to orbit the planet
- Used for satellite television
- Some used for phone networks
Optical fibres
- Use visible light or infrared radiation to transmit large amounts of information very quickly
Speed of a pulse calculation
Speed = speed in vacuum ÷ refractive index
Analog signal
The signal can be any level within a range and varies continuously
Digital signal
The signal has fixed levels - often two; called 0 & 1 - information is sent in poses of fixed duration
Signal regeneration
Removes most of the noise and distortion from the transmission of a signal
Medium
The material through which a wave passes
Effect of having larger vibrations on sound
- Increased amplitude = increased volume
Effect of having faster vibrations on sound
- Increased frequency = Increased pitch
Wave type of a sound wave
Longitudinal wave - particles travel parallel to wave propagation
Compressions
A region of air where the particles are closer together than normal due to a sound wave passing through it
Rarefactions
A region of air where the particles are further apart than normal due to a sound wave passing through it
Direction of movement of compressions and rarefactions
Away from the source of the sound in all directions - spreading the sound wave outwards
Echo
The reflection of a sound wave after hitting a hard surface
Speed of sound in different media
- Air - 343m/s
- Helium gas - 972m/s
- Water - 1500m/s
- Mercury - 1450m/s
- Gold - 3240m/s
- Iron - 5130m/s
- Glass - 5640m/s
- Diamond - 12000m/s
Speed of sound in a vacuum
Sound doesn’t travel in a vacuum because there are no particles to transfer vibrations
Frequency range that the human ear can detect
20-20000Hz
Ultrasound
Sound waves with a frequency above 20000Hz
Uses of ultrasound
- Measure distances using echoes
- Sonar - e.g. measuring depth of the ocean
- Checking for damage in materials - ultrasonic pulse would detect echoes if cracks are present
- Medical scanning
