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Section 3 - Waves
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- 1How do humans see things? (Reflection of waves)1) Visible light is a transverse wave, like all Electromagnetic waves.
2) Reflection of visible light is what allows us to see most objects. Light bounces off them into our eyes.
3) When light reflects from an uneven surface such as a piece of paper, the light reflects off at all different angles and you get a diffuse reflection.
4) When light reflects from an even surface (smooth and shiny like a mirror) then it's all reflected at the same angle and you get a clear reflection.
5) The law of reflection applies to every reflected ray:
Angle of Incidence = Angle of reflection - 2How do you find the: Wave length? Frequency? Amplitude? Period?1) The distance from peak to peak.
2) How many complete waves there are per second passing a certain point - measured in hertz (Hz).
3) Height of the wave (from trough to peak)
4) The time it takes for one complete wave to pass a point.
E.g. a wave with period 0.002s has a frequency of 1 divided by 0.002 = 500hz - 3What is the formula for wave speed?Speed (m/s) = Frequency (Hz) x Wavelength (m)
- 4What is the definition of a transverse wave?In transverse waves the vibrations are at 90 degrees to the direction that energy is transferred by the wave.
- 5Examples of Transverse waves:Light and all other electro-magnetic waves.
- 6What is the definition of Longitudinal waves?In longitudinal waves the vibrations are along the same direction as the wave transfers energy.
- 7Examples of longitudinal waves:1) Sound and ultrasound.
2) Shockwaves. - 8What do all waves transfer and in what direction? Give examples: What else can waves be used as? Give examples:All waves transfer energy in the direction they're travelling in. E.g. microwaves in an oven has their energy transferred to the food when cooking.
Waves can be used as signals to transfer information, e.g. light in optical fibres. - 9What does a reflected wave do? What does a refracted wave do?The waves 'rebound off' the material
The wave goes through the material but changes direction. - 101. What are the 7 types of EM waves? 2. What are the 2 properties shared by EM waves? 3. What do different colours depend on to be different colours?1. Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-rays, Gamma rays.
(Increasing Frequency and decreasing wave length) -------->
2. All are transverse waves and travel at the same speed through free space (vacuum).
3) Depends on wavelength - red has the longest wavelength and lowest frequency, violet is the opposite. - 11What are the uses of Radio waves?1) They have wavelengths longer than 10cm.
2) Long-wave radio (wavelengths of 1-10km) can transmit data around the World. That's because they diffract around the curved surface of the Earth, get around hills and into tunnels.
3) Radio waves are used for TV and FM radio, they have short wavelengths (10cm-10m) and subsequently don't bend around hills or travel far through buildings).
4) Short-wave radio signals can be received at long distances from the transmitter because they are reflected from the ionosphere. - 12What are the uses of microwaves?1) Microwaves have shorter wavelengths than radio waves (1-10cm) but are still used for communication.
2) Satellite communications (satellite TV and phones) use microwaves. But you need to use microwaves with wavelengths that can easily pass through the Earth's watery atmosphere without being absorbed.
3) For satellite TV, the signal from a transmitter is transmitted into space where it's picked up by the satellite receiver dish. This then transmits the signal back to Earth in a different direction where it's received by a satellite dish on the ground.
4) Can be used by remote-sensing satellites which can monitor oil spills, track the movement of icebergs and see how much forest has been cut down. - 13Describe the difference between the difference in microwaves used in satellite communication vs cooking:1) Microwaves used in microwave ovens have different wavelengths.
2) These waves are absorbed by the water molecules in the food. - 14What are the uses of Infrared radiation?1) IR is also known as heat radiation.
2) IR is given out by all objects - the hotter the object, the more IR it radiates.
3) The IR of objects can be detected by night-vision equipment which turns it into electrical signals. This is displayed on a screen as a picture.
4) Used in TV remotes. - 15How can light signals travel through Optical Fibres? What are optical fibres used for?1) Visible light can be used for communication using optical fibres (which carry data long distances as pulses of light), visible light is not only for sight.
2) The fibres work by bouncing the waves off the sixes of a very narrow core.
3) The pulse of the light enters the fibre at a certain angle at one end and is reflected again and again until it emerges again at the other end.
4) Optical fibres are used for telephone and broadband internet cables, replacing the old electrical ones. They're also used for medical purposes to 'see inside' the body without having to operate. - 16Describe how visible is used in photography?1) Cameras use a lens to focus the visible light onto a light-sensitive film or electronic sensor.
2) The lens aperture controls how much light enters the camera.
3) The shutter speed determines how long the film/sensor is exposed to light.
4) By varying the aperture and shutter speed, a photographer can capture as much or as little light as they want in their photographs.
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- Physics Fichas sobre Section 3 - Waves, creado por max bresges el 05/02/2018.
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