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🌌 > P5.3 > Flashcards

P5.3 Flashcards

1
Q

What can different substances do to electromagnetic waves

A
  • absorb
  • transmit
  • refract
  • reflect
    They do these in ways that vary with wavelength
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2
Q

What types of diagrams are used to show reflection and refraction?

A

Ray diagrams

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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
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4
Q

In reflection what is the angle of incidence equal to?

A

Angle of reflection

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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.

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6
Q

When in the change in direction higher

A

If the difference in density is higher

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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.

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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.

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9
Q

What do wavelengths determine?

A

It’s determines what happens to the electromagnetic wave

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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)

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11
Q

What does a plastic bin bag absorb and transmit?

A

It’s absorbs visible light BUT transmit infrared.

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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

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13
Q

How do lenses form images?

A

They refract light which changes its direction

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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

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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)
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16
Q

Why can you not set fire to anything with a concave lens?

A
  • concave lens = spreads light out
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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
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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 β€˜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)
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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
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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

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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)
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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
β…„

↑ = 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
Q

What does the distance form the lens to the object effect and how?

A
  • 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
Q

What happens in short sightedness?

A
  • 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
Q

How can we correct short sightedness?

A
  • 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
Q

What happens in long sightedness?

A
  • 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
Q

How can we correct short sightedness?

A
  • 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
Q

What do triangular prisms disperse?

A
  • White light
  • Diff wavelengths (colours) of light travel at diff speeds so they refract by diff amounts
  • So white light through prism = rainbow
31
Q

How do triangular prisms disperse white light?

A
  • 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
Q

How can you investigate refraction of a light using a prism?

A
  • 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)β€”> 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
Q

What happens to opaque objects when light waves hit them

A
  • don’t transmit light and when visible light hits them, they absorb some wavelengths of light and reflect others
34
Q

What does the colour of an opaque object depend on?

A
  • depends on which wavelengths of light are reflected

- red apple = red as wavelengths corresponding to the red part of spectrum are reflected

35
Q

What colours can’t you make?

A
  • red, green and blue (primary colours)

- banana looks yellow because it’s reflecting yellow or red and green light

36
Q

What happens when wavelengths hit white and black objects?

A
  • white objects = reflects all wavelengths of visible light equally
  • black objects = absorbs all wavelengths of visible light (black = lack of visible light p)
37
Q

What happens when wavelengths hit transparent and translucent objects?

A
  • transparent (see through) and translucent (partially see through) transmit light
  • not all light hitting surface is absorbed/reflected = some can pass through objects
38
Q

What happens when waves are reflected or absorbed off transparent/translucent objects?

A
  • 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
Q

How do colour filters work?

A
  • only let particular Ξ» through and filter out diff Ξ» of light = only certain colours (Ξ») are transmitted and the rest are absorbed
40
Q

What colour does a primary colour filter transmit?

A
  • 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
Q

What happens when a blue filter is placed on a red object?

A
  • obj appears black through blue filter = all light reflected by object will be absorbed by the filter
42
Q

What colour does a non primary colour filter transmit?

A
  • let through both Ξ» of light corresponding to that colour and the Ξ»of the primary colours that can be adde together to make that colour
  • e.g. cyan = blue + green so cyan colour filter lets through all Ξ» of light corresponding to cyan, blue and green
43
Q

What do filters do to white light?

A
  • they take away colours from light NOT add colours to light
44
Q

What happens in specular reflection?

A
  • 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
Q

What happens in scattered reflection?

A
  • 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
Q

How can you investigate reflection using a ray box and a mirror?

A
  • 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
Q 
Why does:
Milk look white
Ink looks black
Clouds look white or black 
Sky looks blue
A
  • milk = white because particles scatter all Ξ»
  • ink = black beacuse particles absorb the Ξ»
  • clouds = some particles absorb and some scatter Ξ»
  • sky = molecules in atmoshere are very small and scatter light with short wavelengths such as blue
48
Q

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?

A
  • 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
Q

Why happens when u shine red light on a blue cube?

A
  • 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
Q

What colour comes out of the ray box when you place a red and blue filter?

A

None as both together would absorb the light

51
Q

What does the focal length depend on?

A

Thickness of the lens

- fatter lens = shorter focal length as light spends more time inside the lens and thus refracts more

52
Q

How do you know if an image is virtual?

A
  • it’s virtual if the top of the image is where the rays appear to come from
53
Q

When you shine a torch on a wall in a dark room, why can everyone see it?

A
  • 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
Q

What are the advantages of optical fibres?

A
  • rapid transmission rate of data
  • multiple signals at once
  • output signal is clear
  • noise is not recognised
  • interference is not recognised

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