Topic 6 - Waves Flashcards
What are the two types of waves?
Transverse or longitudinal
Given example of a transverse wave
The ripples on the water surface
Give an example of a longitudinal wave
Sound waves travelling through air
What do longitudinal waves show?
Areas of compression and rarefraction
Describe transverse waves
The oscillations are perpendicular to the direction of energy transfer
What directions do transverse waves vibrate in?
Up-and-down
How does a transverse wave move?
Up-and-down
Describe longitudinal waves
The oscillations are parallel to the direction of energy transfer
How does a longitudinal wave move?
Left and right
Give an example using a guitar string to show that the wave moves?
If you strum a guitar string and create sound waves, the sound waves don’t carry the air away from the guitar and create a vacuum
Give an example using ripples in the water to show that waves move
If you drop a twig into a calm pool of water, ripples fall on the water surface, the ripples don’t carry the water away with them
What is amplitude?
The maximum displacement of a point on the wave away from its undisturbed position
What is wavelength?
The distance from a point on one wave to the equivalent point on the adjacent wave
What is frequency?
The number of waves passing through a point each second
What is the equation to calculate a period?
Period (secondsw) = 1/frequency (hertz)
What is wave speed?
The speed at which the energy is transferred (or the wave moves) through the medium
What is the wave equation?
Wave speed (m/s) = frequency (hertz) x wavelength (m)
What are the three ways that you can measure the speed of a wave?
- using oscilloscope to measure the speed of sound
- Measure the speed of water ripples using a strobe light
- use the wave equation for waves on strings
When are waves reflected?
At the boundary between two different materials
When can waves be absorbed or transmitted?
At the boundary between two different materials
What are the three things that can happen to waves at the boundary between two different materials?
Reflection, absorption and transmission
What is the equation for the angle of incidence and reflection?
Angle of incidence = angle of reflection
What happens when a wave is absorbed?
Energy is transferred to the materials energy stores
What happens when waves are transmitted?
They carry on travelling through the new material which often leads to refraction
When does specular reflection happen?
When a wave is reflected in a single direction by a smooth surface
What is diffuse reflection?
When a wave is reflected by a rough surface the reflected rays are scattered in lots of different directions
Why are rays reflected in lots of directions during diffuse reflection?
Because the normal is different for each incoming ray which means the angle of incidence is different
What happens when light is reflected by a rough surface?
The surface appears matte and there isn’t a clear reflection of objects
What happens when the soundwave travels through a solid?
It causes vibrations in the solid as it travels fast
What causes the sensation of sound in the ear?
Soundwaves cause the eardrum and other parts to vibrate
What restricts the limits of human hearing?
The conversion of soundwaves and vibrations in solids, works over a limited frequency range
What is the range of normal human hearing?
20 Hz to 20 kHz
What else limits human hearing?
This size and shape of our eardrum, the structure of all the other parts in our ear that vibrate to transfer energy
What happens when vibrations are felt in the ear?
They are passed on to tiny bones called ossicles through the semicircular canals and to the cochlea which turns them into electrical signals and sent to the brain
How do soundwaves pass through the surrounding medium?
As a series of compressions and rare fractions
Why can’t sound travel in space?
Because it’s mostly a vacuum so there are no particles to move or vibrate
Why can’t humans hear Ultrasound waves?
They have a higher frequency than the upper limit of hearing for humans
What happens to Ultrasound waves when they meet a boundary between two different media?
They are partially reflected
How do you determine how far away a Boundary is when ultrasound meets it?
The time taken for the reflections to reach a detector can be used to determine how far away such a Boundary is
What are the uses of ultrasound?
Medical and industrial imaging
Why can Ultrasound waves be used for medical and industrial imaging?
Because we can determine how far away a Boundary is
How are seismic waves produced?
earthquakes
What are P – waves?
Longitudinal seismic waves that travel at different speeds through solids and liquids
What are S – waves?
Transverse seismic waves that cannot travel through a liquid
What do you P – waves and S – waves provide evidence for?
The structure and size of the earths core
What is echo sounding and what is it used for?
Echo sounding, using high-frequency soundwaves is used to detect objects in deep water and measure water depth
What did the study of seismic waves provide new evidence for?
It provided new evidence that led to discoveries about parts of the Earth which are not directly observable
What are electromagnetic waves?
Transverse waves that transfer energy from the source of the waves to an absorber
What do electromagnetic waves form?
A continuous spectrum and all types of electromagnetic waves travel at the same velocity through a vacuum or air
How are waves in the electromagnetic spectrum grouped?
In terms of their wavelength and their frequency
What is the order of the electromagnetic spectrum?
Radio waves, microwaves, infrared radiation, visible light, ultraviolet, x-rays, gamma rays
Which wave in the electromagnetic spectrum has the longest wavelength and lowest frequency?
Radio waves
Which wave in the electromagnetic Spectrum has the shortest wavelength and the highest frequency?
Gamma rays
Which waves can our eyes detect?
Visible light so we detect a limited range of electromagnetic waves
Give an example to illustrate the transfer of energy by electromagnetic waves
A hot object transfers energy by emitting infrared radiation, which is absorbed by the surrounding air
What does a varied wavelength cause?
Different substances may absorb, transmit, refract or reflect electromagnetic waves in different ways that vary with wavelength
What is refraction caused by?
The difference in velocity of the waves in different substances
How can radio waves be produced?
Oscillations in electrical circuits
What happens when radio waves are absorbed?
They may create an alternating-current with the same frequency as the radiowave itself, so radio waves can induce oscillations in electrical circuit
What can changes in atoms and the nuclei of atoms result in for electromagnetic waves?
Electromagnetic waves being generated or absorbed over a wide frequency range
What do gamma rays originate from?
Changes in the nucleus of an atom
What is the issue with ultraviolet waves, x-rays and gamma rays?
They can have a hazardous perfect on human body tissue
What do the effects of ultraviolet waves, x-rays and gamma rays depend on?
The type of radiation and the size of the dose
What is radiation dose measured in?
Sieverts
What is radiation dose?
A measure of the risk of harm resulting from an exposure of the body to the radiation
What is one sievert also equivalent to?
1000 millisieverts = 1 sievert
What are the effects of ultraviolet waves?
They can cause skin to age prematurely and increase the risk of skin cancer
What are the effects of x-rays and gamma rays?
They are ionising radiation that can cause the mutation of genes and cancer
What are the practical applications of radio waves?
Television and radio
What are the practical applications for microwaves?
Satellite communications and cooking food
What are the practical applications for infrared radiation?
Electrical heaters, cooking food and infrared cameras
What are the practical applications for visible light?
Fibre-optic communications
What are the practical applications for UV light?
Energy-efficient lamps, suntanning
What are the practical applications for x-rays and gamma rays?
Medical imaging and treatments
How do satellites use microwaves?
For satellite TV, the signal from a transmitter is transmitted into space where it is picked up by the satellite receiver dish orbiting the Earth which then transmits the signal back to the Earth in a different direction where it’s received by satellite dish on the ground
Why is there a slight time delay between the signal being sent and received using satellites?
Because of the long distance the signal has to travel
How do microwave ovens use microwaves?
The microwaves need to be absorbed by water molecules in foods and penetrate up to a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food causing the water to heat up
Why can infrared radiation be used to increase monitor temperature?
Infrared radiation is given out by all hot objects, the hotter the object, the more infrared radiation it gives out
How do infrared cameras work?
The camera detect the infrared radiation and turns it into an electrical signal which is displayed on the screen as a picture, the hotter the object is, the brighter it appears
What happens to objects when they absorb infrared radiation?
The temperature increases
How do electrical heaters use infrared radiation?
They contain a long piece of wire that heats up when a current flows through it which then emits lots of infrared radiation which is absorbed by objects and the air in the room. Energy is transferred by the infrared waves to the thermal energy stores of the objects, causing the temperatures to increase
How do fibre-optic cables use visible light to transmit data?
The light rays are reflected back and forth until they reach the end of the fibre to carry data
What are optical fibres?
Thin glass or plastic fibres that can carry data over long distances as pulses of visible light
Why do fluorescent colours look so bright?
Fluorescence is a property of certain chemicals where ultraviolet radiation is absorbed and visible light is emitted
How do you fluorescent lights work?
They generate UV radiation which is absorbed and reemitted as visible light by a layer of phosphorus on the inside of the bulb so they are energy-efficient and a good use when light is needed for long periods
How does ultraviolet give you a tan?
- UV light is produced by the Sun and exposure to it gives you a tan
- UV lamps can be used to give an artificial suntan however overexposure can be dangerous
How are x-rays used?
Radiographers in hospitals take x-ray photographs to see if people have broken bones as x-rays pass easily through flesh but not as easyily through denser material like bones
How are x-rays and gamma rays used to treat people with cancer?
High doses of these rays kill all living cells, so they are carefully directed towards cancer cells to avoid killing too many normal healthy cells
How is gamma radiation used as a medical tracer?
A gamma emitting source is injected into the patient and its progress is followed around the body, gamma radiation is well suited to this because it can pass out through the body to be detected
How does a lens form an image?
By refracting light
How is light brought to focus in a convex lens?
Parallel rays of light are brought to a focus at the principal focus
What is the focal length?
The distance from the lens to the principal focus
What are ray diagrams used to show?
The formation of images by convex and concave lenses
Describe the image produced by a convex lens?
It can be either real or virtual
Describe the image produced by a concave lens?
It is always virtual
How do you calculate magnification?
Magnification = Image height/objects height
How will convex lenses be represented in ray diagrams?
With outward facing arrow heads
How will concave lens is be represented in ray diagrams?
With inward facing arrow heads
What are the 6 descriptions of an image in a ray diagrams?
Real or virtual
Upright or inverted
Magnified or diminished
How is each colour within the visible light spectrum identified?
Each colour within the visible light spectrum has its own narrow band of wavelength and frequency
How do colour filters work?
They work by absorbing certain wavelengths and transmitting other wavelengths
How is the colour of an opaque object determined?
By which wavelengths are more strongly reflected
What happens to wavelengths that are not reflected?
They are absorbed
What happens if all wavelengths are reflected equally?
The object appears white
What happens if all wavelengths are absorbed by the object?
The object appears black
How can object that transmit light be described?
Transparent or translucent
What do all bodies (object) do?
All bodies, no matter what temperature, emit and absorb infrared radiation
What is a perfect black body?
An object that absorbs all of the radiation incident on it
Does a black body reflect or transmit any radiation?
Neither
Why would a perfect blackbody be the best possible emitter?
Because a good absorber is also a good emitter
What is a body at constant temperature doing?
Absorbing radiation at the same rate as it is emitting radiation
When does the temperature of a body increase?
When the body absorbs radiation faster than it emits radiation
What does the temperature of the Earth depend on?
- The rate of absorption and emission of radiation
- reflection of radiation into space
