Light Flashcards
Diffuse reflection
incident beam from parallel light reflects (scatters) in all directions
example of diffuse reflection
light from paper you read from
regular reflection
incident beam from parallel light is reflected as a beam of parallel light
example of regular reflection
light reflected from a highly polished surface
why does the glass in a household mirror complicate things?
because the light bends as it enters and exits
Law 1 of reflection
the incident ray, the reflected ray and the normal all lie in the same plane
Law 2 of reflection
the angle of incidence equals the angle of reflection
i=r
normal
an imaginary line perpendicular to the mirror
where are angles of incidence and reflection measured from?
the normal
glancing angle
between the mirrors and the beam of light
if you rotate a plane mirror by angle a, what happens to the reflected ray?
the reflected ray is deflected by an angle 2a
whats special about the image in a plane mirror?
u=v
u
distance from object to mirror
v
distance from mirror to image
type of image in a plane mirror 2
virtual
laterally inverted
what is a virtual image
rays of light do not pass through a virtual image they just appear to do so
a person 2m tall needs to see all of himself in the mirror, what length does it have to be? where should he place it?
1m, half way from the ground to the height of his eyes
p
pole
explain p
the centre of the mirror itself
c
centre of curvature
explain c
the centre of the sphere from which the mirror was cut
f
focal point
explain f
half way between c and p
focal length
distance between p and f
straight line that joins p f and c
principal axis
m
magnification
m = (2)
v/u = image distance/ object distance
1/f =
1/u + 1/v
real image v
posituev
virtual image v
negative
concave mirror f
positive
convex mirror f
negative
nature of image, when object at infinity (very far away)
formed on focal point, real image
nature of image, when object a little outside c
image between c and f
real inverted diminished
nature of image, when object at c
real, inverted and diminished, image at c
nature of image, when object between c and f
image is real inverted and magnified
nature of image, when object on f
image at infintiy. real, inverted, greatly magnified
nature of image, when object inside f
located behind the mirror, virtual erect and magnified
nature of image, when object anywhere in convex mirror
image behind the mirror, inside f
virtual, erect and diminished
an object is placed 16cm in from of a concave mirror and an inverted image is formed 24cm in front of mirror. object is 2cm in size. calculate the focal length of the mirror and the size of the object
u= 16cm f = 9.6cm
an image formed in a concave mirror of focal length 12cm is 3 times the size of the object. calculate the positions of the object for this to happen
u=16cm or 8cm
2 uses of concave mirror
shaving or makeup mirror to give enlarged image
dentists mirror for enlarged image of a tooth
2 uses of a convex mirror
security mirror in a shop
rear view mirror of a car (image is smaller, more is seen)
definition of refraction of light
the bending of light as it passes from one medium to another of a different refractive index
Law 1 of refraction
the incident ray, the refracted ray and the normal all lie in the same plane
Law 2 of refraction
Snell’s law
The sin of the angle of incidence is proportional to the sine of the angle of refraction
sin i/sin r =
n
refractive index of glass refers to
the refractive index of air to glass
directly proportional graph
straight line graph through the origin
c1/c2 =
n
c1
speed of light in medium 1
c2
speed of light in medium 2
speed of light in air
2.99 x 10 to the power of 8
real depth/apparent depth =
n
state of no parallax
coincides even when you move right and left
why should you avoid small values in experiments
they lead to greater percentage error
one thing to avoid in light experiments
avoid the error of parallax when measuring distances
real dept vs apparent depth, y vs x axis
real depth y axis apparent dept x axis (slope is n = real over apparent)
critical angle
the angle in the more dense medium when the angle of refraction in the less dense medium is 90 degrees
1/sinC=?
w n a
outside layer of optical fibre called
cladding
where does total internal reflection happen in an optical fibre?
at the boundary between the fibre and the cladding
lense dense material in optical fibre
cladding
how long will total internal reflection happen for in the fibre
ntil the light exits from the far end of the fibre
2 uses of total internal reflection
in the telecommunications industry
in medical endoscopes
3 reasons why it is better to use optical fibres instead of copper wire in the telecommunications industry
cheaper
non-corrosive
more information can be transmitted along the
why wouldn’t light bend in an experiment to show total internal reflection when passing through the glass the first time?
you shine it through on the normal
dispersion of white light
the breaking up of a beam of light into its constituent colours which spread out to form a spectrum
lamba 1 over lamba 2=
n
when showing the recombination of a spectrum into white light, what should you label the angles as?
60 degrees
what is the same/different about the 2 prisms to recombine a spectrum into white light
also equiangular
near sides are parallel
inverted though
why does light reflect at 90 degrees in total with a normal looking right angled triangle at the end of it
periscope
enters along normal, no bending angle of incidence is 45 degrees critical angle is 42 reflects back at 45 degrees add them up it looks like 90 degrees
why is light reflected back along its own path when entering flat hypothenuse of right angled triangle
bike reflectors
goes in through normal no bending
at 45 degrees to side, total internal reflection at another 45
hits other side,at 45 and does the same thing
45 +45 = 90
plus another one
= 180 degrees
Concave mirror: light at infinity
2
Image on f
Real
Concave mirror: object outside c
Image real inverted and diminished
Concave mirror: object on c
Image real inverted and same size
*** Concave mirror: object between c and f
Image real, inverted and magnified
Concave mirror: object on f
Image at infinity
Real and greatly magnified
** Concave mirror: object inside f
Image is virtual erect and magnified
Convex mirror: anywhere in front of mirror
Image is virtual erect and diminished
How do you get the focal length from a graph when given v and u values
Plot 1/u vs 1/v and f is 1/slope
How do you find circle of light at the top of water when the bulb is underneath?
Use n=1/sinC to get C
Using C find the radius of the circle
pi r squared
Converging lens: object between 2f and f
Real inverted and magnified
Converging lens: object inside f
Image on the left of the lens
Virtual erect and magnified
Diverging lens: object anywhere on the left side of the lens
Image on the left side of the lens
Virtual erect and diminished
