Chapter 14 - Light Flashcards
what is important to remember about the angle of incidence when a light wave reflects?
it will equal the angle of reflection
why do the reflected and incident waves have the same wavelength?
they have the same frequency and travel at the same speed
what do light rays show?
the direction the light waves are moving in
what is the normal?
a line that is perpendicular to the mirror
what is the angle of incidence?
the angle between the incident ray and the normal
what is the angle of reflection?
the angle between the reflected ray and the normal
what three things is an image that is formed by a plane mirror?
virtual, upright and laterally inverted (back to front)
what is a virtual image?
one that is formed at the place where light rays appear to come from after they have been reflected
why can you see a clear image when you look in a mirror?
it has a smooth surface for specular reflection
what is specular reflection?
reflection from a smooth surface where parallel light rays are reflected in one direction
what is diffuse reflection?
reflection from a rough surface results in light rays being spread in different directions
what happens when each point on the incident wavefront reaches a barrier?
it creates a wavelet
what do wavelets do?
line up with other reflected wavefronts to create the reflected ray
what happens to the direction of a light ray when it travels into a material that is denser?
it moves towards the normal
the angle of refraction is smaller than the one of incidence
what happens to the direction of a light ray when it travels into a material that is less dense?
moves away from normal
angle of refraction is greater than the one of incidence
what is refraction?
when a wave crosses a boundary between materials and is refracted
why does refraction occur?
waves travel at different speeds in different densities
what is partial reflection?
when some waves cross are reflected at a boundary and others lose energy so are refracted
what is different about each colour?
different frequency and wavelength
what is a transparent object?
something that transmits all the light entering the object
what is a translucent object?
something that lets light pass through it but the light is scattered or refracted
why are objects translucent?
they have lots of internal boundaries so the direction of the light changes repeatedly
what is an opaque object?
something that absorbs all light that hits it
how do appliances emit different coloured lights?
they emit different wavelengths of light
how do colour filters work?
they absorb and transmit certain wavelengths
what are the three primary light colours?
red, green and blue
why are red, green and blue the three primary colours?
they can be mixed to produce any other colour of light
what do pigments do?
absorb light of specific wavelengths and strongly reflect the rest
why is a white surface white?
it has no pigments
it reflects all light that hits it
why is a red book red?
it has pigments that absorb all of the colours apart from red, which it reflects
what is produced when all of the primary colours are combined?
white light
what happens when light hits a black object?
all light is absorbed
what do colour filters do?
filters wavelengths so only certain ones are absorbed or transmitted
what would a blue filter do?
absorb all the colours apart from blue, which it reflects and transmits
how does a lens work?
it changes the direction of the light passing through it
what does a convex lens do?
it makes parallel light rays converge to a focus
what is the principal focus/focal point of a lens?
where the parallel rays are focused to
use of convex lens? 3
magnifying glass
camera
correct long sightedness
what does a concave lens do?
makes parallel light rays spread out (diverge)
what is the principal focus of a concave lens?
where the rays appear to have come from
use of concave lens?
correct short sightedness
what is the focal length of a lens?
the distance from the lens to the principal focus
equation for magnification from a lens
image height / object height
if the magnification of an object is greater than 1, what does it tell you?
the image is bigger than the object
if the magnification of an object is less than 1, what does it tell you?
the image is smaller than the object
what is a real image?
something that can be formed on a screen
what does a convex lens do?
it bulges outwards and causes light rays to converge at the principal focus
what does a concave lens do?
bulges inwards and causes light rays to diverge at principal focus
what is an axis?
a line passing through the centre of the lens
what is the principal focus of a convex lens?
where the rays meet
what is the principal focus of a concave lens?
where the rays appear to have come from
what is the focal length?
the distance from the centre of the lens to the principal focus
what are the three rules for refraction in a convex lens?
a ray parallel to the axis refracts through the lens and passes through the principal focus
a ray passing through the principal focus will refract through the lens and travel parallel to the axis
a ray passing through the centre of the lens carries on in the same direction
what are the three rules for refraction in a concave lens?
a ray parallel to the axis refracts through the lens and appears to have come from the principal focus
a ray passing through the lens towards the principal focus will refract and travel parallel to the axis
a ray passing through the centre of the lens carries on in the same direction
what is a virtual image?
when rays diverge so the light from an object appears to be coming from a different place
what three things do you need to say about an image to describe it properly?
upright/inverted
real/virtual
magnified/diminished
what does the image created by a lens depend on? 2
the focal length of the lens
the distance between the object and the lens
what will an image formed by a concave lens always be?
virtual, upright and diminished
what type of lens is used in a camera?
convex
when is a real image formed by a convex lens?
when the object is further away from the principal focus
