p5.3 Flashcards
what do you use a ray diagram to show?
what happens when electromagnetic waves hit a boundary/travel through matter
what is the law of reflection (and where is it only true)
angle of incidence = angle of reflection
- only true for plane mirrors
when describing an object formed by a plane mirror what 3 points must you describe?
- whether the object is real/virtual
- whether the object is inverted/upright
- whether the object is diminished/magnified
what is a virtual image?
image that is formed where light rays appear to come from
what is an upright image?
when the image is the same way up as the object
where does specular reflection occur?
- from a smooth surface
what is the difference between specular and diffuse reflection?
specular = occurs from smooth surface diffuse = occurs from rough surface
what is the difference between specular and diffuse reflection in terms of the clarity of the image?
(and how is it produced)
s = parallel rays reflected in the same direction
CLEAR IMAGE
d = parallel rays SCATTERED in different directions
UNCLEAR IMAGE
what do lenses do?
refract light passing through them
define the principal focus?
the point where parallel rays meet/appear to meet
what is the focal length?
the distance from the lens to the principal focus
define what a convex lens does
refracts parallel rays passing through it CONVERGE to a point
give 3 uses of convex lenses
- magnifying lens
- camera forming an image of an object far away (needs to focus, not refract light)
- correcting long sight
define what a concave lens does
and give one use
refracts parallel rays passing through it to DIVERGE
- correcting short sight
difference between rays travelling from nearby objects vs distant objects
- 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)
what is a real image?
image that is formed where light rats meet
what is the difference between virtual and real images (ie. where they focus)
virtual = focus inside focal length
real = focus outside focal length
what kind of lens are real images made from?
converging/convex lens
what kind of lens are virtual images made from?
can use both a convex and concave lens
- only convex = object must be inside focal point
- concave = object must be outside focal point
define an inverted image
image is upside down compared to object
in what scenario would an image appear magnified?
when an object is placed inside the focal length of a converging/convex lens (but a virtual image)
equation to calculate magnification?
object height
similarities between concave and convex lenses?
S - both can be used both ways
- both refract light
- both have a principle focus on both sides of lens
differences between concave and convex lenses?
D - concave produces only virtual images
- convex produces virtual + real images - concave refracts light rays outwards - convex refracts light rays inwards
at which point are images formed?
where all light rays from a point of an object appear to come together
which 3 places must you draw a light ray coming off an object from in a ray diagram?
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
what kind of image is formed from a diverging lens?
virtual, upright, diminished
what is the principal axis?
an imaginary line running horizontally through the middle of the lens
why cannot concave lenses produce a real clear image?
as the light rays do not focus (so must be dotted backwards)
how do you represent a concave lens?
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how do you represent a convex lens?
/\
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how does the thickness of lenses affect their focal lengths? (and why)
thicker lens = shorter focal length
- as light spends more time travelling through a thicker lens, so would end up being bent more
define dispersion
separating a ray/ a wave (usually of white light) into its individual wavelengths/frequencies
why do the different ‘colours’/ wavelengths refract by different amounts in glass?
different wavelengths of EM radiaton travel at different speeds within glass
in terms of the visible light spectrum colours, which colour is refracted the most/least and why
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)
in terms of absorption, why would an object appear blue under white light?
as it reflects only the frequency of blue, but absorbs all other frequencies of white light (ie. red, green, yellow)
what are the 2 ways surfaces can reflect light rays (and what does that depend on)?
specular reflection
diffuse scattering
- depends on the type of material
what kind of image does specular reflection produce?
- give example material
- and why does it do that
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)
what kind of image does diffuse scattering produce?
- give an example of a material which has this
- and why it does this
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
how does a filter appear red?
as it absorbs all the other frequencies, and only allows the frequency of red light to pass through
what is black?
not an actual colour, only the absence of light/ a certain wavelength of light
is white light a colour?
no, it is a combination of all the wavelengths and colours
all frequencies of light travel at the same speed in a ……….. however, different frequencies travel at different speeds in ….. ………
vacuum any medium (ie. glass, water)
what happens if a light ray enters a medium perpendicular to the boundary?
it carries on in a straight line (no direction change, as it is already at the normal)
how will glass interact with UV radiation?
absorb it
how will glass interact with IR radiation?
reflect it
what causes light to spread out creating a rainbow effect once it passes through a prism?
- different wavelengths in light refract different amounts because different wavelengths all travel at different speeds
- it also hits glass at an angle
what happens if a light ray enters glass at an angle?
part of the wave that hits the boundary first gets slowed down before the rest (changes angle of whole ray)
