Light-Refraction Flashcards
define refraction
The bending of light rays when they pass obliquely from one medium to another medium is called refraction of light.
what is the cause of refraction
Refraction is caused due to the change in speed of light when it enters from one medium to another
give the lws of refraction
i)the incident ray, the refracted ray and the normal to the interface to the interface of the two transparent media at the point of incidence all lie in the same plane.
ii) the ratio of the sine of the angle of incidence to the sine of the angle of reflection is a constant, for the light of a given colour and for a given pair of media. this is also known as snell’s law of refraction. it is also the refractive index of the second medium with respect to the first.
n=sin i/sin r
what happens when the light ray passes from a rarer medium to a denser medium
the light ray bends towards the normal.
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what happens when the light ray passes from a denser medium to a rarer medium
the light ray bends away from the normal.
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what is the incident ray
A ray of light falling on the surface separating two mediums is the incident ray.
what is the refracted ray
A ray of light traveling in another medium, with change in direction is the refracted ray.
what is the emergent ray
the refracted ray which emerges out from a medium after refraction is called emergent ray.
in a rectangular glass slab, why is the incident ray parallel to the emergent ray?
the extent of bending of light at the opposite parallel faces of the rectangular glass slab are equal and opposite, so the rays are parallel.
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what is lateral displacement
The perpendicular distance between the original path of incident ray and the emergent ray coming out of glass slab is called lateral shift or lateral displacement of the emergent ray of light.
give the factors on which lateral shift depends on
-Directly proportional to the thickness of glass slab.
-Directly proportional to incident angle.
- Directly proportional to the refractive index
of glass slab.
-Inversely proportional to the wavelength of light
define refractive index
refractive index of a medium is the measure of the change in speed of light when it enters that medium
define absolute refractice index
absolute refractive index of a medium is the ratio of the speed of light in air to the speed of light in that medium.
it is denoted by (n)
n=c/v
c=speed of light in air
v=speed of light in medium
why is absolute refractive index never greater than 1
Since c > v, therefore absolute refractive index (n) of a medium is always greater than unity (i.e. 1)Refractive index is a pure number. It has no unit.
define relative refractive index
relative refractive index of medium 2 to medium 1 is the ratio of the speed of light in medium 1 to speed of lighr medium 2
give the factors on whcih refractive index depends on
Nature of material of the medium
Density of the medium
Colour of wavelength of light
define lens
Lens is a transparent material bound by two surfaces, of which one or both surfaces are spherical.
define convex lens
A lens having both spherical surfaces or one spherical surface and other plane surface such that it is thick in the middle and thin at the edges is known as convex lens.
define concave lens
A lens having both spherical surfaces or one spherical and other plane surface such that it is thin in middle and thick at the edges is known as concave lens.
define principal axis of lens
an imaginary straight line passing through the centres of curvature of the spherical surfaces forming the lens is called principal axis
define optical centre of the lens
the central point of the lens through which the light rays pass undeviated is called the optical centre. it is denoted by “O”
define aperture of lens
the effective diameter of the spherical outline of the lens is called aperture
define principal focus
a point on the principal axis where all the rays parallel to the principal axis meet or appear to meet after refraction is called principal focus
