p5.3

Question 1

what do you use a ray diagram to show?

Answer 1

what happens when electromagnetic waves hit a boundary/travel through matter

Question 2

what is the law of reflection (and where is it only true)

Answer 2

angle of incidence = angle of reflection

• only true for plane mirrors

Question 3

when describing an object formed by a plane mirror what 3 points must you describe?

Answer 3

• whether the object is real/virtual
• whether the object is inverted/upright
• whether the object is diminished/magnified

Question 4

what is a virtual image?

Answer 4

image that is formed where light rays appear to come from

Question 5

what is an upright image?

Answer 5

when the image is the same way up as the object

Question 6

where does specular reflection occur?

Answer 6

• from a smooth surface

Question 7

what is the difference between specular and diffuse reflection?

Answer 7

specular = occurs from smooth surface 
diffuse = occurs from rough surface

Question 8

what is the difference between specular and diffuse reflection in terms of the clarity of the image?
(and how is it produced)

Answer 8

s = parallel rays reflected in the same direction
CLEAR IMAGE

d = parallel rays SCATTERED in different directions
UNCLEAR IMAGE

Question 9

what do lenses do?

Answer 9

refract light passing through them

Question 10

define the principal focus?

Answer 10

the point where parallel rays meet/appear to meet

Question 11

what is the focal length?

Answer 11

the distance from the lens to the principal focus

Question 12

define what a convex lens does

Answer 12

refracts parallel rays passing through it CONVERGE to a point

Question 13

give 3 uses of convex lenses

Answer 13

• magnifying lens
• camera forming an image of an object far away (needs to focus, not refract light)
• correcting long sight

Question 14

define what a concave lens does

and give one use

Answer 14

refracts parallel rays passing through it to DIVERGE

- correcting short sight

Question 15

difference between rays travelling from nearby objects vs distant objects

Answer 15

• nearby = seem to be diverging from each other (so lens has to be thick to focus to a specific point)
• distant = seems to be traveling parallel to each other (so lens refracts light a lot less)

Question 16

what is a real image?

Answer 16

image that is formed where light rats meet

Question 17

what is the difference between virtual and real images (ie. where they focus)

Answer 17

virtual = focus inside focal length

real = focus outside focal length

Question 18

what kind of lens are real images made from?

Answer 18

converging/convex lens

Question 19

what kind of lens are virtual images made from?

Answer 19

can use both a convex and concave lens

• only convex = object must be inside focal point
• concave = object must be outside focal point

Question 20

define an inverted image

Answer 20

image is upside down compared to object

Question 21

in what scenario would an image appear magnified?

Answer 21

when an object is placed inside the focal length of a converging/convex lens (but a virtual image)

Question 22

equation to calculate magnification?

Answer 22

object height

Question 23

similarities between concave and convex lenses?

Answer 23

S - both can be used both ways

• both refract light
• both have a principle focus on both sides of lens

Question 24

differences between concave and convex lenses?

Answer 24

D - concave produces only virtual images

- convex produces virtual + real images    - concave refracts light rays outwards
- convex refracts light rays inwards

Question 25

at which point are images formed?

Answer 25

where all light rays from a point of an object appear to come together

Question 26

which 3 places must you draw a light ray coming off an object from in a ray diagram?

Answer 26

1) line diagonally from top of object through optical centre + down NO CHANGE DIRECTION 2) line drawn from top of object, parallel to principle axis and refracted down (through the principle focus on right) 3) lens passes through principle focus on left (from topi of object and refracts parallel to axis (only for object outside focal point) MUST ALWAYS HAVE ONE RAY PARALLEL + ONE RAY DIAGNOL THROUGH OPTICAL CENTRE

Question 27

what kind of image is formed from a diverging lens?

Answer 27

virtual, upright, diminished

Question 28

what is the principal axis?

Answer 28

an imaginary line running horizontally through the middle of the lens

Question 29

why cannot concave lenses produce a real clear image?

Answer 29

as the light rays do not focus (so must be dotted backwards)

Question 30

how do you represent a concave lens?

Answer 30

\/ | | /\

Question 31

how do you represent a convex lens?

Answer 31

/\ | | \/

Question 32

how does the thickness of lenses affect their focal lengths? (and why)

Answer 32

thicker lens = shorter focal length | - as light spends more time travelling through a thicker lens, so would end up being bent more

Question 33

define dispersion

Answer 33

separating a ray/ a wave (usually of white light) into its individual wavelengths/frequencies

Question 34

why do the different 'colours'/ wavelengths refract by different amounts in glass?

Answer 34

different wavelengths of EM radiaton travel at different speeds within glass

Question 35

in terms of the visible light spectrum colours, which colour is refracted the most/least and why

Answer 35

smaller wavelength = more refraction blue light refracted the most, red light refracted the least (blue light slows down the most, red light slows down the least)

Question 36

in terms of absorption, why would an object appear blue under white light?

Answer 36

as it reflects only the frequency of blue, but absorbs all other frequencies of white light (ie. red, green, yellow)

Question 37

what are the 2 ways surfaces can reflect light rays (and what does that depend on)?

Answer 37

specular reflection diffuse scattering - depends on the type of material

Question 38

what kind of image does specular reflection produce? - give example material - and why does it do that

Answer 38

sharp images - plane mirror - as a mirror obeys the law of reflection and so the parallel rays interacting with the mirror leave parallel to it (in a uniform direction)

Question 39

what kind of image does diffuse scattering produce? - give an example of a material which has this - and why it does this

Answer 39

no images - sheet of paper - paper scatters light rays (causes light rays to leave at non-parallel angles) - so light cannot be focused to make an image

Question 40

how does a filter appear red?

Answer 40

as it absorbs all the other frequencies, and only allows the frequency of red light to pass through

Question 41

what is black?

Answer 41

not an actual colour, only the absence of light/ a certain wavelength of light

Question 42

is white light a colour?

Answer 42

no, it is a combination of all the wavelengths and colours

Question 43

all frequencies of light travel at the same speed in a ........... however, different frequencies travel at different speeds in ..... .........

Answer 43

``` vacuum any medium (ie. glass, water) ```

Question 44

what happens if a light ray enters a medium perpendicular to the boundary?

Answer 44

it carries on in a straight line (no direction change, as it is already at the normal)

Question 45

how will glass interact with UV radiation?

Answer 45

absorb it

Question 46

how will glass interact with IR radiation?

Answer 46

reflect it

Question 47

what causes light to spread out creating a rainbow effect once it passes through a prism?

Answer 47

- different wavelengths in light refract different amounts because different wavelengths all travel at different speeds - it also hits glass at an angle

Question 48

what happens if a light ray enters glass at an angle?

Answer 48

part of the wave that hits the boundary first gets slowed down before the rest (changes angle of whole ray)