polycet physics materials

1. AP POLYCET 2018 STUDY MATERIAL FOR
PHYSICS(EM)
SBTET, AP, AMARAVATI

2. CHAPTER 7
Human Eye and Colourful World
Summary:
• The maximum angle, at which humans can see the whole object is called
angle of vision.
• The angle of vision for a healthy human being is about 600
.
• It varies from person to person and with age.
• Humans can see an object comfortably and distinctly when held at a
distance of 25 cm.
• This distance of 25 cm is called least distance of distinct vision.

3. • The eye ball is nearly spherical in shape.
• The front portion is covered by a transparent
protective membrane called the ‘cornea’.
• Behind the cornea, filled with a liquid called aqueous humour and
behind this a crystalline lens.
• It is responsible for the image formation.
• Iris, is the coloured part, is the muscular diaphragm, with a small
hole, called pupil.
• Iris controls the amount of light entering the eye through ‘pupil’.
• Iris makes pupil to act as a “variable aperture” for light to enter into
the eye.
• The light that enters the eye forms an image on the
retina.
• The distance between the lens and retina is about 2.5
cm
• The image distance is fixed and is 2.5 cm for any
position of object.
• the focal length of a lens depends on its material and
radii of curvature of lens.
• The eye lens can change its shape with the help of ciliary muscle
attached to it which change its focal length by changing the radii of
curvature.
• The process of adjusting focal length of lens is called
“accommodation” of lens.
• The eye-lens forms a real and inverted image of an object on the
retina.

4. • Retina contains 125 million receptors called “rods and cones”
which receive the light signals.
✓ Rods identify the Intensity of light,
✓ Cones identify the colour.
✓ These are transmitted to the brain through the optic
nerve fibres.
• The vision becomes blurred due to “ accommodation defects” of
the eye.
Defects of Eye:
• There are mainly three defects of eye.
1. Myopia:
✓ Cannot see objects at long distances.
✓ Also called- near or short sightedness.
✓ For these people, focal length is < 2.5 cm.
✓ Image forms before the retina.
✓ A concave lens is used to correct myopia.
Hypermetropia:
✓ Cannot see objects at short distances.
✓ Also called far or long sightedness.
✓ For these people, focal length is > 2.27 cm.
✓ Image forms beyond the retina.
✓ A biconvex lens is used to correct hypermetropia.
Presbyopia:
✓ The ability of eye decreases with age.
✓ Near point disappears.
✓ Difficult to see the nearby objects clearly and
distinctly.
✓ Due to weakening of ciliary muscles and flexibility
of eye lens.
✓ Is wide spread in aged people.
✓ A person can suffer from both Myopia and
hypermetropia with aging.
✓ To correct this defect of vision, bi - focal lenses
which contain both concave and convex lenses.
✓ Upper portion is concave part, and lower convex
part.
Power of Lens:
✓ It is the degree of convergence or divergence of light
rays by a lens.

5. ✓ IT is the reciprocal of focal length in metre.
✓ P = 1/f
✓ Unit is dioptre.
✓ Denoted by D
Multiple choice questions:
1. The least distance of distinct vision is about ________
a) 25 cm b) 50 cm c) 30 cm d) 15 cm
2. The distance between eye lens and retina is about ______
a)10 cm b) 2.5 cm c)2 cm d) 5 cm
3. The maximum focal length of eye lens is about ________
a) 2.5 cm b) 2.2 cm c)3 cm d) 1.5 cm
4. The power of lens is 1D then focal length is________
a) 100 cm b) 50 cm c) 25 cm d) 75 cm
5.Myopia can be corrected by which lens________
a) concave lens b) convex lens c) concavo-convex
d) Plano convex
6. The size of the object is perceived by an eye depends on _____
a) size of the object b) distance of the object from the eye
c) aperture of the pupil d) size of image on retina
7. A doctor advised to use 4D lens. The focal length of the lens is
a) 25 cm b) 400 cm c) 4 cm d) 40 cm
8. Which part of the human eye helps the lens to change its focal length?
a) Retina b) Pupil c) ciliary muscle d) cornea
9. For every position of an object in front of the human eye, the image
distance is fixed at
a) 1 cm b) 1.5 cm c) 2.5 cm d) 0.25 cm
10. To correct one’s hypermetropia defect, the type of lens used is _____
a) biconvex b) biconcave c) concavo- convex
d) planoconcave
KEY
1. a 2. b 3. a 4. a 5. a 6. b
7. a 8. c 9. c 10. a

6. Dispersion and Scattering of Light:
• Refractive index of prism, n = (Sin (A + D)/2)/Sin (A/2)
Where n = refractive index of the prism,
A = Angle of prism, D = Angle of deviation
• The splitting of white light into colours (VIBGYOR) is called
Dispersion.
• The colours of Rainbow are due to dispersion of the sunlight by
millions of tiny water droplets.
• In refraction the frequency of light wave in one medium is same in
both the media, i.e, frequency remains unaltered (will not change),
but wavelength changes.
• v = n λ, where v = speed of light, n = frequency, λ = wave length.
• The process of re-emission of absorbed light in all directions with
different intensities by atoms or molecules, is called “scattering of
light”.
• Sir C.V. Raman invented the Scattering of light.
• Raman experimentally found the frequency of scattered light is
greater than the frequency of incident light. This is called
“ Raman Effect”.
• Raman effect is used to determine the shapes of molecules.
Multiple choice questions:
1. With an increase in angle of incidence of light ray on a prism, the
angle of deviation__
a) remains constant b) first increases and then decreases

7. c)first decreases and then increases d) first increases and then
remains constant.
2. The scientific work of C.V. Raman is on
a) dispersion of light b) total internal reflection
c) defection of vision d) scattering of light
3. Scattering of light involves the process of
a) bending of light at the interface of two media
b) splitting of light into different colours
c) convergence of light rays at the focus
d) re -emission of absorbed light
4. Blue of sky is explained by
a) scattering of light b) total internal reflection
c) refraction of light d) dispersion of light
5. The sun appears red colour during sunset and sunrise, due to
a) scattering of red light is very small b) scattering of red light is high
c) scattering of other colours is high d) none of these
KEY
1. c 2. d 3. d 4. a 5. a