Waves (6) - Pt2 Flashcards
What are microwaves used for?
• microwaves – satellite communications, cooking food
What are infrared waves used for?
• infrared – electrical heaters, cooking food, infrared cameras
What’s visible light used for?
- visible light – fibre optic communications
- fibre optic communications-thin glass or plastic fibres that can carry data (eg from computers) over long distances
- they work of reflections the light rays bounce back and forth till they reach the end of the fibre
- the lights not easily absorbed/scattered as it travels along a fibre
What are ultra violet waves used for?
• ultraviolet – energy efficient lamps, sun tanning
What are x-rays and gamma radiation used for?
• X-rays and gamma rays – medical imaging and treatments
Which are the most dangerous EM waves?
- high frequency waves UV, X-rays and gamma rays transfer lots of energy so cause lots of damage
- low frequency waves like radio waves don’t transfer a lot of energy so pass through soft tissue without being absorbed
Why is UV radiation dangerous?
- It damages surface cell, this leads to sunburn and can cause skin to age prematurely
- can also cause blindness and an increased risk of skin cancer
What makes X-rays and gamma rays dangerous?
- they’re ionising radiation (they carry enough energy to knock electrons off atoms)
- this can cause gene mutation or cell destruction and cancer
What does the danger of each wave depend on?
How much energy the wave transfers
What’s radiation dose?
(Measured in sieverts)
- a measure of the RISK of harm from the body being exposed to radiation
- it depend on how much is absorbed and what type of radiation it is and what are of the body is effected
How do lenses work?
They firm imaged by refracting light ans changing its direction
What are the properties of a convex lens?
- curves outwards
- causes light parallel to the axis to converge at the principle focus
What’s the properties of a concave lens?
- caves inwards
- causes parallel rays of light to spread out (diverge)
What the axis of a lens?
Is a line passing through the middle of the lens
What’s the principle focus of a convex lens?
Where the rays hitting the lens parallel to the axis all meet.
What’s the principle focus of a concave lens? And what’s the focal length?
The point where rays hitting the lens parallel to the axis appear to all come from
(The distance from the centre of the lens to the principle focus is called the focal length)
What happens when a ray hits the centre of a convex or a concave lens?
-it carries on in the same direction
What’s a real image?
Where the light from an object comes together to form an image in a screen
What’s a virtual image?
- When the rays are diverging, so the light from the object appears to be coming from a completely different place
- you can’t project a virtual image onto a screen
What are examples of virtual images?
- a mirror image (because it looks like your behind the mirror)
- a magnify lens (the image looks bigger than it actually is)(the object being magnified needs to be closer to the lens then the focal length)
What kind of image does a convex lens produce?
either real or virtual
What kind of image does a concave lens produce?
always virtual
When describing an image what 3 things do you need to mention?
- size compared to the original object
- upright or inverted
- if it’s virtual or real
What are the properties of a virtual image?
- the right way up
- smaller then the orignal object
- on the same side of the lens as the object
What’s the formula to the magnification of something?
Magnification = image height / object height
Do colour filters work?
Colour filters work by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour).
What does the colour of an opaque object depend on?
- which wavelengths of light are more strongly reflected.
- Wavelengths that are not reflected are absorbed.
- If all wavelengths are reflected equally the object appears white.
- If all wavelengths are absorbed the objects appears black.
What are translucent and transparent objects?
Objects that transmit light
What are the primary colours of light? What do you get when mix the primary colours?
- primary colours are ones you can’t make by mixing: red, blue and green
- mixed together they make white light
Why does a banana loo yellow?
- it reflecting yellow light
- or its both red and green light
What colour would a red object look if your looking at it through a blue filter? And why?
Black
All the light reflected by the object is absorbed by the filter?
