P5.3 Flashcards
(54 cards)
1
Q
What can different substances do to electromagnetic waves
A
- absorb
- transmit
- refract
- reflect
They do these in ways that vary with wavelength
2
Q
What types of diagrams are used to show reflection and refraction?
A
Ray diagrams
3
Q
How do you draw a ray diagram
A
- using a ruler and pencil, draw lines to represent rays
- draw the normal at 90 degrees to the surface at the point the rays hits
- measure the angle between the normal and the rays
- add arrow to show direction
4
Q
In reflection what is the angle of incidence equal to?
A
Angle of reflection
5
Q
Why are electromagnetic waves refracted
A
When light goes from air into glass or a denser medium at an angle, it slows and bends towards the medium.
6
Q
When in the change in direction higher
A
If the difference in density is higher
7
Q
How is reflection used in terms of radio waves?
A
The earth is curved so to send radio waves long distances you have to reflect them from a layer of the atmosphere called the ionosphere. It’s a low frequency wave so it’s less that 30MHz and has long wavelengths.
8
Q
What are high frequency waves and what are they used for?
A
They have a frequency of over 30MHz and are used for satellite communications through the atmosphere due to their short wavelength.
9
Q
What do wavelengths determine?
A
It’s determines what happens to the electromagnetic wave
10
Q
What do walls transmit and absorb?
A
They can transmit radio and microwaves BUT absorb visible light and ultraviolet (you don’t get sunburnt in a building and very slowly in a greenhouse)
11
Q
What does a plastic bin bag absorb and transmit?
A
It’s absorbs visible light BUT transmit infrared.
12
Q
What does the atmosphere absorb ?
A
- absorbs X -rays and there are no natural X- ray sources
- absorbs Gamma rays from the Sun and space BUT gamma rays can be detected from rocks in your house
13
Q
How do lenses form images?
A
They refract light which changes its direction
14
Q
What is the focal length?
A
- Distance form centre of lens to the principal focus
- principal focus is on each side of lens
15
Q
What is a concave lens, and where is its axis and virtual principal focus?
A
- concave (diverging) lens caves inwards
- causes the parallel rays of light to diverge (spread out)
- axis of lens = line passing though the middle of the lens
- principal focus (focal point) of concave = point where rays hitting the lens parallel to the axis appear to come from (all meet up at point behind lens)
16
Q
Why can you not set fire to anything with a concave lens?
A
- concave lens = spreads light out
17
Q
What is a convex lens, and where is its axis and principal focus?
A
- convex lens (converging) bulges outwards
- causes parallel rays of light to converge (move together)
- principal focus is where rays hitting the lens parallel to axis all meet
18
Q
What are the two types of images that lenses can form?
A
- REAL image = light from an object comes together to form an image on a ‘screen’ (e.g. image formed on an eyes retina)
- VIRTUAL image = rays are diverging so the light from object appears to be coming from a completely different place (e.g mirror = virtual image)
19
Q
Give examples of convex lens are the type of image they form:
A
- magnifying glass = virtual,magnified , upright
- camera,eye = real, diminished, inverted
- projector = real,magnified, inverted
- microscope / telescope = lens near object - real and inverted/ lens near eyes - virtual and upright
20
Q
Give examples of concave lens are the type of image they form:
A
- spy holes in door = virtual, diminished and upright
- back windows of coaches = virtual, diminished and upright
21
Q
How do you draw a ray diagram for an image through a concave lens?
A
- pick point at to of image
- draw ray going from object to lens parallel to axis of lens
- draw ray from top of object to right through middle of lens
- incidence ray that’s parallel to axis is refracted so appears to have come from principal focus (F)= dray ray from F to parallel line (make it dotted till lens = virtual here)
- ray passing through middle of lens doesn’t bend and mark where this ray meets virtual ray (dotted line) = top of image
- repeat for a point on the bottom of image (if bottom of object on axis, then image is also on axis)
22
Q
What kind of image do concave lens produce?
A
- virtual image
- right way up, smaller than object and on same side of lens as object no matter where object is
23
Q
How are concave and convex rays represented in ray diagrams?
A
Y = concave lens
⅄
↑ = convex lens
↓
24
Q
How do you draw a ray diagram for an image through a convex lens?
A
- pick point at top of object and draw ray from it parallel to axis
- draw another ray from top of object going through middle of lens
- incident ray that’s parallel to axis is refracted through F
- ray passing middle doesn’t bend
- where rays meet = top of image
- repeat for bottom of object (if object bottom = axis then image = axis)
25
What does the distance form the lens to the object effect and how?
- distance from lens to object effects size and position of image
- an object 2F (2 focal lengths) from lens = real, inverted image same size as object and at 2F on other side of lens
- an object between F and 2F = real,inverted image bigger than object beyond 2F
- object nearer F makes virtual image the right way up, bigger than object on same side of lens
26
What happens in short sightedness?
- short sighted = can’t focus on distant objects
- eye has convex lens to focus incoming light onto back of retina = where image formed
- if eyeball too strong/long = lens can’t produce focuses image on refine and image of distant objects are brought into focus in front of retina = image is blurry
27
How can we correct short sightedness?
- concave lens
- correct it = put concave lens in front of eye = diverges light before enters the eye = focused onto the refine = produce sharp, clear image
28
What happens in long sightedness?
- long sighted = can’t focus on near by object
- lens is too weak / eyeball is too short
- images of near objects are brought into focus behind the back of the eye = images are blurry
29
How can we correct short sightedness?
- convex lens
- correct = convex lens put in front of eye = light starts to converge before entering the tee = can be focused on retina = clear, sharp image
30
What do triangular prisms disperse?
- White light
- Diff wavelengths (colours) of light travel at diff speeds so they refract by diff amounts
- So white light through prism = rainbow
31
How do triangular prisms disperse white light?
- light bends towards the normal as it enters the prism as glass is denser than air = diff wavelengths/colours of light bend by different amounts (red bends least and violent bends most)
- light bends away from the normal as it leaves a prism and different colours bend by different amounts and due to the prism’s shape this spreads the wavelengths out even more
- on far side of prism= spectrum (rainbow)
32
How can you investigate refraction of a light using a prism?
- need light source, coloured filters and triangular glass prism on piece of paper
- place red filter in front of ray box and shine a thin light beam into prism at an angle to the normal (some light will be reflected)
- trace the incident and emerging rays onto paper and remove prism
- draw refracted ray by joining ends of the other two rays with a straight line (could measure incidence and refraction angle)
- repeat with blue filter (keep incidence angle same)—> blue light refracts more at each boundary
- repeat with more colours/wavelengths (shorter wavelength = more refraction) OR repeat with white so it disperses
- could try changing the shape or material of prism
33
What happens to opaque objects when light waves hit them
- don’t transmit light and when visible light hits them, they absorb some wavelengths of light and reflect others
34
What does the colour of an opaque object depend on?
- depends on which wavelengths of light are reflected
| - red apple = red as wavelengths corresponding to the red part of spectrum are reflected
35
What colours can’t you make?
- red, green and blue (primary colours)
| - banana looks yellow because it’s reflecting yellow or red and green light
36
What happens when wavelengths hit white and black objects?
- white objects = reflects all wavelengths of visible light equally
- black objects = absorbs all wavelengths of visible light (black = lack of visible light p)
37
What happens when wavelengths hit transparent and translucent objects?
- transparent (see through) and translucent (partially see through) transmit light
- not all light hitting surface is absorbed/reflected = some can pass through objects
38
What happens when waves are reflected or absorbed off transparent/translucent objects?
- some wavelengths that may be absorbed or reflected by translucent/(more less likely) transparent objects = these objects appear to be the colour of light that corresponds to the wavelength most strongly transmitted by objects
39
How do colour filters work?
- only let particular λ through and filter out diff λ of light = only certain colours (λ) are transmitted and the rest are absorbed
40
What colour does a primary colour filter transmit?
- only transmits that colour (white light on blue = only blue light let through and rest of the colours are absorbed)
- look at blue obj through blue filter = looks blue as blue is reflected from object’s surfer and transmitted by filter
41
What happens when a blue filter is placed on a red object?
- obj appears black through blue filter = all light reflected by object will be absorbed by the filter
42
What colour does a non primary colour filter transmit?
- let through both λ of light corresponding to that colour and the λof the primary colours that can be adde together to make that colour
- e.g. cyan = blue + green so cyan colour filter lets through all λ of light corresponding to cyan, blue and green
43
What do filters do to white light?
- they take away colours from light NOT add colours to light
44
What happens in specular reflection?
- light bounces off objects into our eyes
- Specular reflection = light rays reflect off smooth surfaces all in the same direction = giving a clear reflection (light on mirror)
45
What happens in scattered reflection?
- light reflects off rough surfaces in all directions = each day hits surface at different angles so if scatters the light
- because normal is different for each incident ray
- if light reflected by rough = surface looks Matt = no clear reflection
46
How can you investigate reflection using a ray box and a mirror?
- take piece of paper and draw solid line across then dotted at 90 degrees (normal)
- place plane (flat) mirror lining with solid line
- using ray box, shine thin beam of white light at the mirror so light hits mirror where normal meets mirror
- trace incident and reflected light rays
- measure angle between incident and normal and the angle between reflected ray and normal
- repeat using varying angle of incidence (incidence always = reflection)
- repeat for diff colours by using colour filters (any colour always should stay same)
- keep test fair by keeping same mirror, same width, brightness of beam
47
```
Why does:
Milk look white
Ink looks black
Clouds look white or black
Sky looks blue
```
- milk = white because particles scatter all λ
- ink = black beacuse particles absorb the λ
- clouds = some particles absorb and some scatter λ
- sky = molecules in atmoshere are very small and scatter light with short wavelengths such as blue
48
For the investigation including a ray box and a mirror, why may a systematic error occur and why may someone’s results be more consistent and how will different colours have an affect on the results?
- surface of the mirror may not be flat or the normal may be drawn incorrectly
- using a sharper pencil or the ray box producing a narrower ray of light causes more consistent results
- coloured light has no affect as angle of incidence is equal to angle of reflection
49
Why happens when u shine red light on a blue cube?
- appears black
- red wavelengths only transmitted by red filter and rest absorbed
- only blue filter reflected by cube and rest absorbed
- so therefore all light reaching the cube is absorbed = looks black
50
What colour comes out of the ray box when you place a red and blue filter?
None as both together would absorb the light
51
What does the focal length depend on?
Thickness of the lens
| - fatter lens = shorter focal length as light spends more time inside the lens and thus refracts more
52
How do you know if an image is virtual?
- it’s virtual if the top of the image is where the rays appear to come from
53
When you shine a torch on a wall in a dark room, why can everyone see it?
- wall = rough so the light from the torch is scattered from the surface (diffused scattering)
- thus wherever you are in the room, torch will reflect from each part of the rough surface into your eye
54
What are the advantages of optical fibres?
- rapid transmission rate of data
- multiple signals at once
- output signal is clear
- noise is not recognised
- interference is not recognised
