Luminous bodies:
Those objects which emit light by themselves are called luminous bodies.
e.g. - sun, stars, electric bulb etc.
Non- luminous bodies:
those objects which do not emit light by themselves but are visible by the
light falling on them emitted by self luminous bodies are called non-luminous
bodies.
A material can be
classified as:
(i)
Transparent:
the substances which allow most of the incident light to pass through them are
called transparent e.g. glass, water.
(ii)
Translucent:
The substances which allow a part of incident light to pass through them are
called translucent bodies e.g. oiled paper.
(iii)
Opaque:
The substances which do not allow the incident light to pass through them are
called opaque bodies. E.g. mirror, metal, wood etc.
Reflection of light:
Light moving in one medium when falls at the surface of another medium, part of
light returns back to the same medium. This phenomenon of returning back of
light in the first medium at the interface of two media is known as reflection
of light.
Laws of reflection
(i)
The incident ray, reflected ray and normal to
the reflecting surface at the incident point all lie in the same plane.
(ii)
The angle of reflection is equal to the angle of
incidence.
Reflection from plane
mirror
(i)
The image is virtual, laterally inverted.
(ii)
The size of image is equal to that of object.
(iii)
The distance of image from the mirror is equal
to distance of object from the mirror.
(iv)
If an object moves towards (or away from) a
plane mirror with speed v, relative to the object the image moves towards (or
away) with a speed 2v.
(v)
If a plane mirror is rotated by an angle θ,
keeping the incident ray fixed, the reflected ray is rotated by an angle 2θ.
(vi)
To see his full image in a plane mirror, a
person requires a mirror of at least half of his height.
(vii)
If two plane mirrors are inclined to each other
at an angle θ the number of images (n) of a point object formed are determined
as follows:
(a)
If 360
/θ is even integer, then n= 360
/θ = 1
(b)
If 360/ θ
is odd integer,
Then n=360/ θ -1 for the object is symmetrically placed and
N = 360 /θ for the objects is not symmetrically placed.
(c)
If 360 /θ are a fraction then n is equal to
integral part.
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