Waves (6) - Pt2

Question 1

What are microwaves used for?

Answer 1

• microwaves – satellite communications, cooking food

Question 2

What are infrared waves used for?

Answer 2

• infrared – electrical heaters, cooking food, infrared cameras

Question 3

What’s visible light used for?

Answer 3

• 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

Question 4

What are ultra violet waves used for?

Answer 4

• ultraviolet – energy efficient lamps, sun tanning

Question 5

What are x-rays and gamma radiation used for?

Answer 5

• X-rays and gamma rays – medical imaging and treatments

Question 6

Which are the most dangerous EM waves?

Answer 6

• 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

Question 7

Why is UV radiation dangerous?

Answer 7

• 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

Question 8

What makes X-rays and gamma rays dangerous?

Answer 8

• they’re ionising radiation (they carry enough energy to knock electrons off atoms)
• this can cause gene mutation or cell destruction and cancer

Question 9

What does the danger of each wave depend on?

Answer 9

How much energy the wave transfers

Question 10

What’s radiation dose?

Answer 10

(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

Question 11

How do lenses work?

Answer 11

They firm imaged by refracting light ans changing its direction

Question 12

What are the properties of a convex lens?

Answer 12

• curves outwards

- causes light parallel to the axis to converge at the principle focus

Question 13

What’s the properties of a concave lens?

Answer 13

• caves inwards

- causes parallel rays of light to spread out (diverge)

Question 14

What the axis of a lens?

Answer 14

Is a line passing through the middle of the lens

Question 15

What’s the principle focus of a convex lens?

Answer 15

Where the rays hitting the lens parallel to the axis all meet.

Question 16

What’s the principle focus of a concave lens? And what’s the focal length?

Answer 16

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)

Question 17

What happens when a ray hits the centre of a convex or a concave lens?

Answer 17

-it carries on in the same direction

Question 18

What’s a real image?

Answer 18

Where the light from an object comes together to form an image in a screen

Question 19

What’s a virtual image?

Answer 19

• 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

Question 20

What are examples of virtual images?

Answer 20

• 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)

Question 21

What kind of image does a convex lens produce?

Answer 21

either real or virtual

Question 22

What kind of image does a concave lens produce?

Answer 22

always virtual

Question 23

When describing an image what 3 things do you need to mention?

Answer 23

• size compared to the original object
• upright or inverted
• if it’s virtual or real

Question 24

What are the properties of a virtual image?

Answer 24

• the right way up
• smaller then the orignal object
• on the same side of the lens as the object

Question 25

What’s the formula to the magnification of something?

Answer 25

Magnification = image height / object height

Question 26

Do colour filters work?

Answer 26

Colour filters work by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour).

Question 27

What does the colour of an opaque object depend on?

Answer 27

• 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.

Question 28

What are translucent and transparent objects?

Answer 28

Objects that transmit light

Question 29

What are the primary colours of light? What do you get when mix the primary colours?

Answer 29

• primary colours are ones you can’t make by mixing: red, blue and green
• mixed together they make white light

Question 30

Why does a banana loo yellow?

Answer 30

• it reflecting yellow light

- or its both red and green light

Question 31

What colour would a red object look if your looking at it through a blue filter? And why?

Answer 31

Black

All the light reflected by the object is absorbed by the filter?