Page 42 - Physics 10_Float

GEOMETRICAL OPTICS

Solution: Given that,p = 6 cm and f = 10 cm
Using the mirror formula, Point to ponder
1 1 1
= –
q f p
Apparent
1 = 1 – 1 position of
q 10 cm 6 cm fish Actual position
of fish
1 = – 1
q 15 cm
q = – 15 cm
Why the position of fish inside
The negative sign indicates that the image is virtual i.e., the water seems to be at less
depth than that of its actual
behind the mirror.
position?
12.4 REFRACTION OF LIGHT
If we dip one end of a pencil or some other object into water
at an angle to the surface, the submerged part looks bent as
shown in Fig.12.7. Its image is displaced because the light
coming from the underwater portion of the object changes
direction as it leaves the water. This bending of light as it
passes from one transparent medium into another is called
refraction.
Refraction of light can be explained with the help of Fig.12.8.
A ray of light IO travelling from air falls on the surface of a
Fig.12.7: Bending of pencil in
glass block. N Normal
Incident ray water due to refraction
I
Physics insight
Angle of i Incident
incidence i Air ray Wavefronts
O r Glass
Angle of Refracted λ λ
ray Air i i
refraction r
R Glass
M λ t
Emerging Transmitted
ray ray
E
Fig. 12.8: Refraction of light by a glass block
In refraction, the speed of light
changes due to change in the
At the air-glass interface, the ray of light IO changes direction and
wavelength. But, frequency
bends towards the normal and travels along the path OR inside and hence the colour of light
the glass block. The rays and OR are called the incident ray and IO does not change.
the refracted ray respectively. The angle ‘i’ made by the incident

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