EXERCISE
Very Short Answers (1 Mark)
1. What is the phenomenon responsible for the blue colour of sky?
Answer: The blue color of the sky is caused by the scattering of sunlight by the Earth’s atmosphere.
2. What is the near and far point of a normal eye?
Answer: The near point of a normal eye is 25 cm, and the far point is infinity.
3. Name the component of eye that is responsible for the adjustment of eye lens?
Answer: The component of the eye responsible for the adjustment of the eye lens is the ciliary muscles.
4. To an astronaut why does the sky appear dark instead of blue?
Answer: The sky appears dark to an astronaut because there is no atmosphere in space to scatter sunlight.
5. How can your remove the defect of vision ‘Presbyopia’.
Answer: Presbyopia can be corrected by using bifocal lenses or progressive lenses.
6. Name three primary colour?
Answer: The three primary colors are red, blue, and green.
7. Write the nature of image formed by our eye?
Answer: The image formed by our eye is real and inverted on the retina.
8. What do you understand by Dispersion of light?
Answer: Dispersion of light is the splitting of white light into its component colors when it passes through a prism.
9. What is Tyndall Effect?
Answer: The Tyndall Effect is the scattering of light by particles in a colloid or in very fine suspensions.
10. A student has difficulty reading the black board while sitting in the last row. What is the defect of vision and how it can be corrected?
Answer: The student has myopia (nearsightedness), and it can be corrected by using concave lenses.
Short Answers (2 Marks)
1. Name the phenomenon responsible for formation of rainbow? Explain it with the help of diagram.
Answer: The formation of a rainbow is due to dispersion, refraction, and total internal reflection of sunlight in water droplets. When sunlight enters a raindrop, it bends (refraction), splits into its component colors (dispersion), and reflects off the inside surface of the droplet before exiting. The result is a spectrum of colors that form a circular arc.
2. What is power of accommodation? How ciliary muscles helps in accommodation?
Answer: The power of accommodation refers to the ability of the eye to focus on objects at varying distances by adjusting the shape of the lens. The ciliary muscles help in this process by contracting or relaxing to change the curvature of the lens, allowing it to become thicker for near objects (increased refractive power) or thinner for distant objects.
3. Why the sun appear red while sunset and sunrise. Explain?
Answer: During sunrise and sunset, the sun is near the horizon, and its light has to pass through a thicker layer of the Earth’s atmosphere. The shorter wavelengths (blue and violet) are scattered out of the line of sight due to Rayleigh scattering, leaving the longer wavelengths (red and orange) to dominate the view, making the sun appear red.
4. Why does the star twinkle but not the earth?
Answer: Stars twinkle because their light passes through various layers of Earth’s turbulent atmosphere, which causes the light to bend slightly (refraction) and appear to shift in brightness. Since stars are point sources of light, this effect is more noticeable. Earth or other planets do not twinkle because they are closer and appear as extended objects, so the changes in light due to atmospheric refraction are less pronounced.
5. Explain the function of(i) Iris (ii) Pupil (iii) Retina
Answer: (i)Iris: The iris is the colored part of the eye that controls the size of the pupil, regulating the amount of light that enters the eye.
(ii) Pupil: The pupil is the black circular opening in the center of the iris that allows light to enter the eye and reach the retina.
(iii) Retina: The retina is the light-sensitive layer at the back of the eye that contains photoreceptor cells (rods and cones). It converts light into electrical signals, which are sent to the brain for image processing.
6. Explain the refraction of light through a glass prism with the help of diagram. Show the angle of emergence and angle of deviation.
Answer: When light passes through a prism, it first bends (refracts) upon entering the prism and then bends again when it exits. This bending causes the light to spread out into its component colors (dispersion). The angle of emergence is the angle between the emergent ray and the normal to the surface. The angle of deviation is the angle between the incident ray and the emergent ray.
Long Answer Type Questions (5 Marks)
1. What is myopia? State the two causes of myopia. With the help of labelled ray diagram show(1) Eye defect(2) Correction of myopia
2. What is hypermetropia. State the two causes? With the help of labelled ray diagram show(1) Eye defect(2) Correction of hypermetropia.
3. Draw the labelled diagram of human eye and explain the image formation.