Page 213 - Physics_Form_2

Refraction and dispersion of light
of the object. Calculate the distance
of the image from the lens.
7. An object is placed at a distance of
25 cm from a convex lens of focal
length 20 cm. Find magnification of
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the image formed.
Chapter summary
1. When light encounters the boundary
between two different optical media,
a portion of the light is reflected and
the remainder is transmitted into the
second medium. The transmitted
light undergoes a change in speed that
causes a change in its direction. This
phenomenon is called refraction.
2. The change in speed and direction
of light depends on the refractive
indices of the two media.
3. Light travelling from a medium of
low refractive index to a medium of
high refractive index is bent toward
the normal.
4. When light passes through a medium
of high refractive index to one of
lower refractive index, total internal
reflection occurs if the angle of
incidence is greater than the critical
angle
5. The use of prisms in binoculars relies
on their ability to totally reflect the
incident light internally.
6. Refraction of light through a glass
prism obeys Snell’s law.
7. The angle formed by the intersection
of the incident ray and the emergent
ray directions is called the angle of
deviation.
Physics Form 2 Final.indd 207
8. The minimum angle of deviation
by a triangular prism occurs when
the angle of incidence produces a
refracted ray that travels parallel to
the base of the prism.
9. Dispersion of light is the splitting
of white light into its component
colours. The split light forms a
spectrum of colours.
10. The spectrum colours of white light
are red, orange, yellow, green, blue,
indigo, and violet.
11. A rainbow is formed as a result of
the refraction and reflection of the
colours of light in raindrops.
12. Colours of objects result from the
reflection and absorption of certain
colours by objects.
13. The mixing of pigments is called
subtractive mixing of colours.
Subtractive complementary colours
combine to produce black.
14. The mixing of coloured lights is
called additive mixing of colours.
Revision Exercise 5
1. Choose the letter of the correct
answer from the given alternatives:
(a) A pin at the bottom of a basin
full of water appears to be 6 cm
from the surface. Given that the
refractive index of the water is
4/3, what is the actual distance
of the pin from the surface?
(i) 1.33 cm (ii) 4.85 cm
(iii) 7.33 cm (iv) 8.0 cm
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