6. Waves Flashcards
What are longitudinal waves?
Waves in which the oscillations are parallel to the direction of energy transfer.
What are transverse waves?
Waves in which the oscillations are perpendicular to the direction of energy transfer.
What is the peak/crest?
The highest point above the rest position.
What is the trough?
The lowest point below the rest position.
What is amplitude?
The maximum displacement of a point of a wave from its rest position.
What is wavelength?
The distance covered by a full circle of the wave, usually measure from peak to peak or trough to trough- usually measured in (m). From one point on the wave to the same point on another wave.
What is compression?
Regions of high pressure due to particles being close together.
What is rarefaction?
Regions of low pressure due to particles being spread further apart.
What is a period?
The time it takes for two successive crests (one complete wave) to pass a point.
What is frequency?
The number of waves passing a point every second.
Period = 1/ frequency (what are the units?)
Period in seconds (s)
Frequency in herts (Hz)
Velocity= frequency x wavelength (what are the units?)
Velocity in metres per second (m/s)
Frequency in herts (Hz)
Wavelength in metres (m)
What is the definition of transmit?
To cause (light, heat, sound etc) to pass through a medium.
What is the definition of absorb?
To take in or soak up (energy, liquid or another substance) by chemical or physical action.
What is refraction?
Where a wave changes direction when it meets a boundary between 2 media. Less dense to more dense = wavelength decreases, speed decreases, frequency remains the same.
What is the law of reflection?
i = r
What is the range of normal human hearing?
From 20 Hz to 20 kHz.
What does the amplitude of the wave show?
How loud the wave is.
What does the frequency of the wave show?
The pitch of the waves- how many oscillations per second
Are sound waves transverse or longitudinal?
Longitudinal.
What are some facts about P waves?
They are longitudinal and travel at different speeds through solids and liquids.
What are some facts about S waves?
They are transverse and cannot travel through a liquid.
What is echo sounding?
Echo sounding- using high frequency sound waves- is used to detect objects in deep water and measure water depth
What speed to electromagnetic waves travel at?
They all travel at the same speed, the speed of light, 300,000,000 m/s
What is the order of the electromagnetic spectrum from the lowest to highest frequency?
Radio waves
Microwaves
Infrared radiation
Visible light
Ultraviolet
X-rays
Gamma rays
How do radios work?
When radio waves strike the receiving antenna, they push the electrons in the metal back and forth, creating tiny oscillating currents which are detected by the receiver. They oscillate with the wave’s frequency. Other aerials absorb the radio waves and create an alternating current with a frequency that matches the radio waves.
What are radio waves produced by?
Oscillations in electrical circuits
How do microwaves work?
Microwaves are absorbed by water and fat molecules making water and fat molecules vibrate more. This energy is then conducted into the rest of the food.
What does ionising mean?
The waves have enough energy to remove electrons from atoms.
What is the use of radio waves?
Communication- e.g. television and radio because they don’t cause damage to humans and long wavelength travel far.
What are the uses of microwaves?
Cooking food and satellite communications because the frequencies are easily absorbed by food molecules and can penetrate the atmosphere
What are the uses of infrared radiation?
In electrical heaters, cookers and infrared cameras because the frequencies that are absorbed by some chemical bonds lead to the internal energy increasing. They can be absorbed by the skin and generate heat.
What are the uses of visible light?
Fibre optic communications because that is the light we can see and have low energy loss
What are the uses of ultraviolet light?
To kill bacteria present in water, for security tagging, detergents and crime investigations because the light can kill bacteria to sterilise and absorb and emit fluorescence
What are the uses of x-rays and gamma rays?
Medical imaging, cancer treatment and food irradiation because x-rays can penetrate soft tissues and are absorbed by denser materials and gamma rays are highly penetrating so effective for cancer treatment and sterilisation
What are the hazards of UV radiation?
- they are ionising at higher frequencies
- they cause skin damage
- they increase risk of skin cancer
What are the hazards of X-rays?
- they are ionising radiation which lead to cellular damage and DNA mutations
- repeated exposure increases cancer risk
What are the hazards of gamma rays?
- they are ionising, penetrating and cause deep internal tissue damage
- cause radiation sickness and genetic mutations
- prolonged exposure increases cancer risk
What is a body?
An object when we talk about IR, all bodies no matter what temperature emit and absorb IR.
How does temperature affect bodies?
- a body at a constant temp is absorbing radiation at the same rate as it is emitting it
- the hotter a body, the more IR it radiates in a given time
- the temp of a body increases when the body absorbs radiation faster than it emits radiation
What is a perfect black body?
A perfect black body is a theoretical object that would absorb all the radiation that falls incident on it and would not reflect or transmit any radiation. It would also be the best possible emitter.
What factors affect the temp of the earth?
- rate of absorption of radiation
- rate of emission of radiation
- reflection of radiation into space
What is specular reflection?
Reflection from a smooth surface in a single direction.
What is diffuse reflection?
Reflection from a rough surface that causes scattering
How does colour work?
The light reflected back into the eyes determines the colour.
How do colour filters work?
They absorb certain wavelengths and transmit other wavelengths. Wavelengths that are transmitted can be seen.
What colour has the longest and shortest wavelength?
Red has the longest wavelength and violet has the shortest wavelength.
What is a real image?
Real images can be projected onto a screen (on the opposite side of the lens from the object)
What are virtual images?
Virtual images cannot be projected onto a screen (on the same side of the lens as the object)
What does upright mean?
The same way up as the object
What does inverted mean?
Upside down (compared with the object)
What does magnified mean?
Magnified images are bigger than the object
What does diminished mean?
Images that are smaller than the object.
What is the focal length?
The distance between the lens and the principal focus (where parallel light rays (from a distant object) will be focused)
How to draw ray diagrams?
- Line through the centre of the lens from object
- Line from object parallel and then through focal point
- Line through the focal point and then parallel
