Light Flashcards
how are light rays drawn
straight line with an arrow to indicate direction of travel
what are the 3 types of beams of light
parallel, convergent, divergent
why are shadows formed
light travels in straight lines and cannot bend around an opaque object and reach behind it
what is an umbra
totally dark and sharp shadow as no light reaches behind the object
what is a penumbra
partial shadow due to some light reaching behind the object
when does a lunar eclipse occur
when Earth moves directly between Sun and Moon (only on a night of full moon)
when does a solar eclipse occur
when Moon moves directly between Sun and Earth
what is the difference between transparent, translucent and opaque materials
transparent materials allow most of the light to pass through
translucent materials allow some light to pass through
opaque materials do not allow light to pass through
what is the incident ray
light ray striking surface of object
what is the point of incidence
point at which the light is in contact with surface
what is the reflected ray
light ray that bounces off mirror
what is the normal
imaginary line perpendicular to surface at point of incidence
what are the 2 Laws of Reflection
angle of incidence is equal to angle of reflection
incident ray, reflected ray and normal at point of incidence all lie on same plane
3 points
describe a regular reflection
when a parallel beam of light falls on a smooth surface, the reflected rays are parallel
reflections from smooth surfaces called regular or specular reflections
image formed is clear and undistorted
3 points
describe an irregular reflection
when a parallel beam of light falls on a rough surface, the reflected rays are scattered in different directions
reflections from rough surfaces called irregular or diffused reflections
no images or blurred images produced
5 points
describe an image formed by a plane mirror
image is:
1) upright
2) of the same size as object
3) at the same distance behind mirror as object is from mirror
4) virtual (cannot be reflected onto a screen behind the mirror)
5) laterally inverted
what are concave mirrors
they have a surface that bends inwards and form virtual and magnified images if object is sufficiently close to the mirror
what are convex mirrors
they have a surface that bends outwards and form images that are upright, distorted and smaller than object
what is refraction
bending of light when it travels from one transparent medium to another transparent medium
what is the refracted ray
light ray which is refracted
*bends more towards normal if light travels slower
*opposite side of normal as incident ray
what is the emergent ray
light ray that bends away from the normal as it emerges from a medium back into the air
*parallel to incident ray
what happens when the incident ray is perpendicular to surface of a medium (travelling along normal)
refraction will not take place, even though there is slowing down of light as it travels in the medium
objects appear higher in water than it actually is in our eyes
what is this perceived depth called
apparent depth
what is the refractive index
ratio of the speed of light in a vacuum (c) to the speed of light in a medium under consideration (v)
*has no units
what are 2 formulae to calculate refractive index
n = speed of light in vacuum (c) / speed of light in medium (v)
n = sin i / sin r, where i is the angle of incidence, r is the angle of refraction
*i will always be bigger than r and i is always in the air
*n must always be larger than 1
what is the Principle of Reversibility
a light ray will travel along the same path if its direction of travel is reversed
*applies to reflection and refraction of light
what is dispersion
the splitting of white light (sunlight) into colours of the rainbow when passing through a glass prism
*red slows down the least, violet slows down the most
*emergent rays bend again but in a different direction (opposite to incident rays)
what are the 7 colours of the rainbow
red, orange, yellow, green, blue, indigo, violet (ROYGBIV)
*this band of 7 colours called the spectrum of white light
what is a colour filter
any plastic or glass of a specific colour that only lets through that part of the coloured visible spectrum and the remaining part is absorbed
*if red and blue colour filters used together, no light passes through
what are the 3 primary colours of light
red, green, blue (RGB)
*can be mixed to produce white light
what are the 3 secondary colours of light
red + blue = magenta
red + green = yellow
blue + green = cyan
what colour does a blue object appear as under magenta light
blue (reflects blue, absorbs red)
