Flashcards in Section 2 - Waves & The Electromagnetic Spectrum Deck (64):
What do waves do?
Waves transfer energy and information in the direction that ey are travelling
What are the two types of waves?
What is amplitude?
Amplitude is the displacement from the rest position to a crest or trough
What is wavelength?
Wavelength is the length of a full cycle of the wave (e.g. From crest to crest)
What is frequency?
Frequency is the number of complete cycles of the wave passing a certain point per second
Frequency is measured in hertz (Hz)
What is the period of a wave?
The period of a wave is the number of seconds it takes for one full cycle
How do you calculate the period of a wave?
1 (divided by) frequency
Give 3 examples of transverse waves
1) all electromagnetic waves - e.g. light
3) Ripples and waves in water
Transverse waves have _ _ _ _ _ _ _ _ vibrations
Transverse waves have sideways vibrations
Longitudinal waves have _ _ _ _ _ _ _ _ vibrations
Longitudinal waves have parallel vibrations
What are the two calculations for wave speed?
1) distance (divided by) time
2) wavelength x frequency
Give 2 examples of longitudinal waves
1) sound waves
How can you use an oscilloscope to measure sound?
1) set up the oscilloscope so the detected waves at each microphone are shown as separate waves
2) start with both microphones next to the speaker, and then slowly move one away until the two waves are aligned on the display, but have moved exactly one wavelength apart
3) measure the distance between the microphones to find out one wavelength
4) then use the formula frequency x wavelength to find the speed of the sound waves passing through the air. The frequency is whatever the set signal generator was set to in the first place
How do you measure the speed of water ripples in a tank?
1) using a signal generator, you can create a wave at a set frequency
2) turn on the strobe light - a pattern should be seen made by the shadows of the wave crests on the screen below the tank
3) alter the frequency of the strobe light until the wave pattern begins to stop moving. This happens when the frequency of the waves and the strobe light are equal - the waves appear not to move because they are being lit at the same point in their cycle each time
4) the distance between each shadow is the distance between the lines that are 10 wavelengths apart, then find the average wavelength
5) use the fi mule frequency x wavelength to calculate the speed of the waves
How do you use peak frequency to find the speed of waves in solids? (Hammer and metal rod experiment)
1) measure and record the length of the metal rod
2) position a microphone at the end of the metal rod, which should be hung using clamps and elastic bands.
3) tap the rod with a hammer, and write down the peak frequency displayed by the computer
4) repeat this three times to get an average peak frequency
5) calculate the speed of the wave using frequency x wavelength, where the wavelength is equal to twice the length of the rod
What is a ray diagram?
A ray diagram shows the path that a wave travels. You can draw one for a refracted light ray
When a wave meets a boundary, what three things can happen?
1) it can be absorbed by the second material
2) it can be transmitted through the second material
3) it can be reflected away from the second material
What is refraction?
Where the angle and speed of a wave changes when it enters a new medium (meets a boundary)
How does sound travel?
Sound travels as a wave
What are sound waves caused by?
Recall the process of how sound information reaches the brain through the ears
1) the sound is sent down the ear canal, and reaches the eardrum
2) the eardrum vibrates. These tiny vibrations are sent on to tiny bones called ossicles (hammer, anvil and stirrup).
3) these vibrations are passed through the semicircular canals and to the cochlea
4) the cochlea turns these vibrations into electrical signals. The cochlea contains hairs which correspond to a specific pitch in the sound wave
5) these electrical signals are sent down the auditory nerve which leads to the brain, where the signals will be interpreted
What is the human range of hearing?
What is ultrasound?
Ultrasound is a sound that has frequencies higher than the human range of hearing (above 20,000Hz)
Give 2 examples of using ultrasound in technology
1) medical imaging - e.g. Pre-natal scanning of a foetus
2) industrial imaging - e.g. Finding flaws in materials
What is infrasound?
Infrasound is a sound below the range of human hearing (below 20Hz)
Earthquakes and explosions cause seismic waves. True or false?
What substances can p-waves travel through
Solids and liquids
Can p-waves travel through the Earth's core?
Yes, because they can travel through both solids and liquids. This is because the outer core is liquid. S-waves can only travel through solids, and are therefore refracted away from the core.
What substances can s-waves travel through?
Are p-waves transverse or longitudinal?
Are s-waves transverse or longitudinal?
Which wave is faster? S-waves or p-waves?
P-waves are faster than s-waves
What are ray diagrams used to show?
What angle is the angle of incidence equal to?
Angle of reflection
What is total internal reflection?
Total internal reflection is where a wave hitting a surface is reflected back into the material
What are the two types of reflection?
Specular and diffuse
How can you investigate refraction? Refer to an experiment
1) place a rectangular glass block on a plain piece of paper and trace around it.Use a ray box to shine a ray of light at the middle of one side of the block.
2) trace the rays on each side of the block. Draw a straight line through the block to join the two rays of light
3) draw on the normal, and measure the angles with a protractor. Do the same for the point where the ray emerges from the block
4) repeat this three times, keeping the angle of incidence the same. Then, calculate averages for each of the angles
If a white light is shone on a blue filter, what colour light will pass through?
Blue will move through the filter, whereas all other colours will be absorbed (white light contains all colours)
What are the two different types of lenses?
The _ _ _ _ _ of a lens increases with its curvature
The power of a lens increases with its curvature
The power of a converging lens is _ _ _ _ _ _ _ _
The power of a _ _ _ _ _ _ _ _ _ lens is negative
What are the two types of image that can be formed by lenses?
1) real image
2) virtual image
What is a real image?
A real image is formed when the light rays actually come together to form the image. The image can be captured on a screen, because the light rays actually meet at the place where the image seems to be.
e.g. the image formed on the eye's retina
What is a virtual image?
A virtual image is when the light rays from the object appear to be coming from a completely different place to where they're actually coming from. The light rays don't actually come together at the point where the image seems to be, so it cannot be captured on a screen.
e.g. magnifying glasses create a virtual image
What EM wave has the longest wavelength?
What EM wave has the shortest wavelength?
What is the order of the EM spectrum, from longest wavelength to shortest?
Radio, micro, infrared, visible light, ultraviolet, x-ray, gamma
What is the only part of the EM spectrum that our eyes can detect?
What are some dangers of microwaves?
Some wavelengths can be absorbed, causing heating of calls which could be dangerous
Being near electronic devices such as mobile phones - it isn't clear the extent of what the waves can do to human cells
What are dangers of infrared and visible light?
Infrared can cause burns if the skin gets too hot
Both infrared and visible light are mostly reflected or absorbed by the skin, which can cause burns
What are dangers of ultraviolet?
UV is absorbed by skin, but at a higher frequency, so it is potentially more dangerous.
It is a type of ionising radiation, and when absorbed it can cause damage to cells on the surface of the skin, which can result in skin cancer.
Can also damage your eyes, which can lead to a variety of eye conditions, or even blindness
What are dangers of x-rays and gamma rays?
Both of these waves are ionising, so they can cause mutations and damage cells, which can lead to skin cancer
Have even higher frequencies, and transfer even mor energy, causing even more damage.
They can be absorbed by deeper tissues in the body, which can cause more serious conditions
Every object _ _ _ _ _ _ _ and emits EM radiation
Every object absorbs and emits radiation
What colour surfaces emit radiation better: black or white?
How are radio waves made?
What are radio waves mainly used for?
Communication and broadcasting
What are microwaves and radio waves used for?
Used in microwave ovens and satellites
What can infrared be used for?
To monitor temperatures using infrared cameras
Thermal imaging is used by police to see suspects that are trying to escape/ hide in the dark
Can infrared transfer information?
Yes - can be used to send files between mobile phones or laptops.
Infrared is used in TV remote controls
Optical fibres can carry data using pulses of infrared radiation
Give an example of using visible light
Photography - digital cameras contain image sensors which detect visible light
What is ultraviolet commonly used for?
Security pens can be used to mark property, and then if shone under a UV light, it can be detected
Bank notes and passports detect forgeries
Can be used to sterilise water, as it kills bacteria in the water
What are x-rays commonly used for?
Can be used in hospitals to see broken bones
Used in airports to see inside passenger's luggage