Light and Optics Flashcards
Why does pencil appear bent in water
refraction of light
what happens when light travels from a medium of low optical density to high optical density
the light ray bend towards the normal
why does light ray bend towards the normal when it travels from a medium of low optical density to high optical density (2m)
the velocity of light decreases when light travels from an optically less dense medium to a denser medium
because of this, the angle of refraction is smaller than angle of incidence
what happens when light travels from a medium of high optical density to low optical density
the light ray bends away from the normal
why does light ray bend away from the normal when it travels from a medium of high optical density to low optical density (2m)
the velocity of light increases when light travels from an optically less dense to a denser medium
because of this, the angle of refraction is bigger than angle of incidence
what is the formula for refractive index
n = (speed of light in vacuum/ speed of light in medium) = c/v
c = 3.0 x 10^8 ms-1
what are the laws of refraction of light
2m
- the incident ray, refracted ray and normal meet at one point and are in the same place
- snells law: n1 sin θ = n2 sin θ
n2/n1 = sin θ1/sin θ2
why does an image of a fish appear closer to the water surface
refraction of light
light is refracted closer to the normal when air to water
this causes image to be closer
what is the relationship between the refractive index of a medium, real depth and apparent depth
n = real depth/ apparent depth = H/h
How does total internal reflection happens
it occurs when light travels from a medium of high optical density to low optical density
what happens when incident angle is less than the critical angle
the ray is reflected away from the normal
a weak reflected ray can be detected
what happens when the incident angle is the same as the critical angle
the refracted ray travels along the medium boundary
the reflected ray appears brighter
what happens when the incident angle is greater than the critical angle
no refracted ray
total internal reflection occurs
what is the relationship between critical angle and refractive index
n = 1/sin c
the higher the refractive index of a medium, the smaller the critical angle of the medium
what are examples of natural phenomenas that involve total internal reflection
formation of rainbow
mirage
how does rainbow occur
when light from the sun enters water droplets, the light experiences refraction and disperses into different colors
all these different colors experience total internal reflection on the surface of water droplets
lights rays reflected experience refraction and dispersion again when moving from water to air
colours of the rainbow are seen by the observer
how does mirages occur
1) layers of air above the road have different optical densities. The layer of sir just above the road surface is hotter than the upper layers. The layer of hot air has smaller optical density than cold air.
2) light which travels from the upper layer to the lower layer are gradually refracted away from the normal. When the angle of incidence is greater than the critical angle, total internal reflection occurs.
3) reflected light rays are then gradually refracted towards the normal and reach the eyes of the observer. The observer will see the image of a cloud as a puddle of water on the road surface
what are examples of application of total internal reflection in daily life
prism periscope
optical fibre
cat’s eye reflector
name two types of lenses
convex lenses and concave lenses
what are convex lenses known as
converging lenses
what are concave lenses known as
diverging lenses
why are convex lenses called converging lenses
because light rays that pass through it converge at focal point
why are concave lenses called diverging lenses
because light rays appear to be diverging from a focal point
what is optical centre
point at the centre of the lens. Light rays passing through the optical centre are not reflected
what is principal axis
straight line through the optical centre of a lens and the centre of curvature of both surface of the lens
what is axis of lens
straight line through the optical centre and perpendicular to the principal axis
what is focal point, F
point located at the principal axis of a lens
- for convex lens, light rays parallel to the principal axis will converge at this point after passing through the lens
- for concave lens, light rays parallel to the principal axis appear to diverge from this point after passing through the lens
what is object distance, u
distance between object and optical centre of a lens
what is image distance, v
distance between image and optical centre of a lens
what is focal length, f
distance between focal point, F and optical centre, O of a lens
what is the thin lens formula
1/f = 1/u + 1/v
what are the conditions for the sign convention to be positive
focal length: convex lens
image distance:
- real image
- on the opposite side of the project
what are the conditions for the sign convention to be negative
focal length: concave lens
image distance:
- virtual image
- on the same side as the object
what is the ray diagram, image position, characteristic of image, when object is at infinity
image position:
v = f
image at f
characteristic of image:
real
inverted
diminished
what is the ray diagram, image position, characteristic of image, when object O beyond 2F
image distance:
f < v < 2f
image between F and 2F
characteristic of image
real
inverted
diminished
what is the ray diagram, image position, characteristic of image, when object O at 2F
image position:
v = 2f
image at 2f
characteristic of image
real
inverted
same size of object
what is the ray diagram, image position, characteristic of image, when object O between F and 2F
image position:
v > 2f
image beyond 2F
characteristics of image:
real
inverted
magnified
what is the ray diagram, image position, characteristic of image, when object O at F
image position:
image at infinity
characteristic of image:
virtual
upright
magnified
what is the ray diagram, image position, characteristic of image, when object O between F and optical centre
image position
v> u
characteristics of image:
virtual
upright
magnified
what is the ray diagram, image position, characteristic of image, when object O beyond 2F in concave lens
image position:
between optical centre and focal point
v
what is the ray diagram, image position, characteristic of image, when object O between F
image position:
between optical centre and focal point
v
what is the formula for linear magnification
m = v/u = hi/ho
how does a gemologist use a magnifying glass
identify and evaluate gemstones
how does an astronomer use a telescope
study celestial objects
how does an astronomer use a magnifying glass
to examine eyes
how does an microbiologist use a microscope
to examine various microorganisms
how does a geologist use a microscope
study and identify specimens of rocks and materials
what does a compound microscope made out of
two convex lenses with short focal lengths.
Objective lens has focal strength, fo and eyepiece lens has focal strength, fe. Focal strength fo is less than focal strength fe.
