Light/geometrical optics Flashcards
light
form of energy e.g. crooke’s radiometer, solar panels. travels in straight lines
luminous
makes its own light e.g. sun
non-luminous
does not make its own light, instead reflect light e.g. moon
reflection
the bouncing of light off an object
diffuse reflection
reflection of light in all directions off a rough surface
laws of reflection
- incident ray, reflected ray and normal at point of incidence all lie on the same plane
- angle of incidence (i) = angle of reflection (r)
regular reflection
reflection of light off a shiny, smooth surface so that angle of incidence = angle of reflection
virtual image
image formed by the apparent intersection of light rays
real image
image formed by the actual intersection of light rays
parallax
the apparent movement of one object relative to another due to the motion of the observer
lateral inversion
in a plane mirror the image is back to front
concave mirror
converging mirror
convex mirror
diverging mirror
focal length formula
1/f = 1/u + 1/v
magnification
m = v/u
m = image height/object height
refraction
the bending of light when travelling from one medium to another
light travelling from rarer to denser medium
refracted towards normal
light travelling from denser to rarer
refracted away from normal
laws of refraction
- incident ray, refracted ray and normal all lie on same plane
- ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant (snell’s law) i.e. sin i/ sin r = n
snell’s law
Sin(i)/Sin(r) = n
n= refractive index when light travels from a vacuum into a medium
refractive index retracing path
it can be said that for any two media x, y: xny = 1/ynx
total internal reflection
when light going from a denser to a rarer medium strikes the second medium at an angle greater than the critical angle, all the light is reflected back into the denser medium
critical angle
the angle of incidence when the angle of refraction is 90 deg. when light is travelling from a denser to a rarer medium
snell’s window
since light can retrace its path it is found that if light is to enter the water from air and arrive at the point P below the surface, only light which strikes the water within a circle of radius r found above will reach P.
if you are underwater and looking up, light can only enter the water through the circle of radius r (snell’s window). product of TIR
refractive index (depth)
n = real depth/ apparent depth
refractive index (speed of light)
n = speed of light in air (c)/speed of light in medium (c2)
uses of TIR
fibre optics, reflective roadsigns, bicycle safety reflector
optical fibre
a very thin transparent solid rod through which light can travel by TIR
*know how to draw
uses of optical fibres
- telecommunications
- endoscope
- used with dentist drill to see inside mouth
mirage
image of the sky seen on the ground. formed due to TIR when light passes through different layers of hot and cold air
advantages of optical fibres
- less energy cost than electrical cables
- smaller than elec. cables to carry same amount of signals
- interference less than in electrical cables
convex lens
converging lens
concave lens
diverging lens
power of a lens
P = 1/f
P = P1 + P2
unit: m^-1
power of accommodation of the eye
the ability of the eye to focus a real image on the retina by changing its focal length using the ciliary muscles
least distance of distinct vision of the eye
smallest distance from which an object can be seen clearly by the eye without strain
short sighted
person can see objects nearby clearly but cannot bring distant objects into focus
fixed with concave lens
long sighted
person can see distant objects clearly but cannot bring nearby objects into focus
corrected with convex lens
converging focusing system of the eye
cornea, lens, aqueous humour, vitrious humour
image formation in retina
real and inverted, brain corrects image by making it upright
