CBSE Class 10 Physics The Human Eye and the Colourful World Worksheet Set D

The Human Eye and the Colourful World

Question. The sky appears dark to passengers flying at very high altitudes mainly because :
(a) Scattering of light is not enough at such heights.
(b) There is no atmosphere at great heights.
(c) The size of molecules is smaller than the wavelength of visible light.
(d) The light gets scattered towards the earth.
Answer: (a)

Question. If a person can see a doll at the far distance, but he cannot have the newspaper in his hands. What lens should he wear to make correct his eyesight ?
(a) Convex lens
(b) Concave lens
(c) Bi-focal lens
(d) Prism
Answer: (a)

Question. The image formed by the retina of the human eye is :
(a) Virtual and erect
(b) Real and inverted
(c) Virtual and inverted
(d) Real and erect
Answer: (b)

Question. The persistence of vision for the human eye is :
(a) \( \frac{1}{10} \) th of a second
(b) \( \frac{1}{16} \) th of a second
(c) \( \frac{1}{6} \) th of a second
(d) \( \frac{1}{18} \) th of a second
Answer: (b)

Question. The light-sensitive cell present on the retina and is sensitive to the intensity of light is :
(a) Cones
(b) Rods
(c) Both rods and cones
(d) None of these
Answer: (b)

Question. The phenomena of light responsible for the working of the human eye is :
(a) Reflection
(b) Refraction
(c) Power of accommodation
(d) Persistence of vision
Answer: (b)

Question. Match the following Column I (a) Carries signals from an eye to the brain (b) Muscle which change snaps of eye-lens (c) A clear window at font (d) Change shape to focus a picture on retina. Column II (i) Ciliary muscles (ii) Eye-lens (iii) Optic nerve (iv) Cornea
Answer: (a) (iii), (b) (i), (c) (iv), (d) (ii).

Fill in the blanks

Question. (a) A short-sighted person cannot see ............ objects clearly. (b) When a ray of light enters a prism, it bends .............. the normal. (c) The blue colour of sky is due to ............... of light.
Answer: (a) distant, (b) towards, (c) scattering.

Very Short Answers Type Questions

Question. Define the term power of accomodation. Write the modification in the curvature of the eye lens which enables us to see the nearby objects clearly ?
Answer: The ability of the eye lens to adjust its focal length, is called the power of accommodation. There should be a contraction of ciliary muscles, that will increase the curvature of the eye lens and becomes thicker, so the focal length of the eye lens will decrease. It will thus enable us to see the objects clearly.

Question. Write the structure of eye lens and state the role of ciliary muscles in the human eye.
Answer: The eye lens of the human eye is a convex lens that is thick in the middle and thin from the edges. It converges the incident light rays and forms the image on retina. Role of ciliary muscles : (a) It changes the shape of the lens in eye to help with focussing. (b) It helps to regulate the flow of aqueous humor in eye.

Question. What happens to the image distance in the normal human eye when we decrease the distance of an object, say 10 m to 1 m ? Justify your answer.
Answer: The image distance will remain unaffected even if we change the object distance because the image is formed on the retina.

Question. A person is advised to wear spectacles with (a) Convex lenses, (b) Concave lenses. What type of defect of vision is he suffering from ?
Answer: (a) Hypermetropia or long-sightedness. (b) Myopia or short-sightedness.

Question. Where do we see (a) concave and (b) convex lens in bifocal lenses ?
Answer: (a) Concave lens—Upper part (b) Convex lens—Lower part.

Question. Name the principle on which a prism form the image of an object ?
Answer: Refraction of light.

Question. What do you mean by a rainbow ?
Answer: Rainbow is a natural spectrum formed in the sky after rain shower due to dispersion of light caused by suspended water droplets in atmosphere.

Question. Give an example in nature which shows that sunlight may be made up of different colours.
Answer: Formation of rainbow.

Question. What is persistence of vision ?
Answer: The image of any object formed on the retina persists for about \( 1/16 \) of a second. This continuance of sensation of eye for sometime even after the removal of the object is called persistence of vision.

Question. What do you mean by far point of human eye ?
Answer: The most distant point at which an object can be seen clearly by the eye is called the far point of the eye.

Question. In the formation of spectrum of white light by a prism which colour is : (a) deviated least ? (b) deviated most ?
Answer: (a) Red, (b) Violet.

Question. Name the type of defect of vision a person is suffering from, if he uses convex lenses in his spectacles for the correction of his vision. If the power of the lenses is +0.5 D, find the focal length of the lenses.
Answer: The person is suffering from hypermetropia which is also knows as far-sightedness. \( f = \frac{1}{P} \times 100 \implies f = \frac{1}{0.5} \times 100 \implies f = 200 \) cm.

Question. What is scattering of light ? Why is the colour of the clear sky blue ? Explain.
Answer: (a) The phenomenon in which a part of the light incident on a particle is redirected in different directions. (b) When sunlight passes through the atmosphere, its fine particles scatter the blue colour more strongly than red. So, the scattered blue light enters our eyes. Hence the sky appears blue.

Short Answers Type Questions

Question. (a) A person is suffering from both myopia and hypermetropia. (i) What kind of lenses can correct this defect? (ii) How are these lenses prepared ? (b) A person needs a lens of power + 3D for correcting his near vision and – 3D for correcting his distant vision. Calculate the focal lengths of the lenses required to correct these defects.
Answer: (a) (i) If a person suffer from both myopia and hypermetropia, such people often require bifocal lenses. (ii) A common type of bifocal lenses consists of both concave and convex lenses. The upper portion consists of a concave lens. It facilitates distant vision. The lower part is a convex lens. It facilitates near vision. (b) For correcting distant vision: Power, \( P = -3 \text{ D} \). Using \( P = 1/f \), \( f = \frac{1}{-3\text{D}} = -0.33 \) m. The focal length is \( -0.33 \) m. The minus sign tells us it is a concave lens. For correcting near vision: Power, \( P = +3 \text{ D} \). Using \( P = 1/f \), \( f = (1/3) = +0.33 \) m. The focal length is \( +0.33 \) m. The plus sign tells us it is a convex lens.

Question. What is atmospheric refraction ? List two phenomena which can be explained on the basis of atmospheric refraction.
Answer:
In atmosphere, there are layers of different densities and refractive indices, when light ray is passed through these layers refraction of light takes place which is called atmospheric refraction.
Two phenomenon that can be explained on the basis of atmospheric refraction are :
(a) Twinkling of stars.
(b) Early sunset and delayed sunrise.

Assertion and Reasoning Based Questions

Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.

Question. Assertion : The Sun appears red during sunrise or sunset.
Reason : The scattering of light is inversely proportional to its wavelength.

Answer: (a)

Question. Assertion : The human eye is one of the most valuable and sensitive sense organs.
Reason : Eye enables us to see the wonderful world and the colours around us.

Answer: (a)

Question. Assertion : The curvature of the eye lens can be modified to some extent by the ciliary muscles.
Reason : The ciliary muscles are used to modify the curvature of lens.

Answer: (a)

Question. Assertion : Sometimes, the eye may gradually lose its power of accommodation.
Reason : The crystalline lens of people at old age becomes milky and cloudy.

Answer: (b)

Question. Assertion : Hypermetropia is also known as near-sightedness.
Reason : The image of a distant object is not formed in front of the iris.

Answer: (d)

Creating Based Questions

Question. Reena was diagnosed with a short-sight problem. She was advised to wear spectacles continuously which made her feel low about her beauty. What would you suggest Reena other than wearing spectacles ?

Answer: When Reena is diagnosed with short-sight problem, the better advice to be considered is that she can wear spectacles. But when she is not comfortable wearing spectacles, I would suggest her to fix lens which won’t degrade her looks and will make her feel confident.

Question. Babin was diagnosed with a long sight problem. He was advised to wear lens but he was worried that wearing lens should be given an utmost care in his busy schedule. What would you suggest Babin other than usage of lens ?

Answer: It was a big problem for Babin to take care of lens in his busy schedule due to this reason I suggested him to undergo laser operation which would correct all common vision problems like near sight, a long sight which reduce the dependency on the lens. The eye treatment using laser is safe and effective.

Question. What would be your suggestion to your grandfather who is undergoing the eye defects both hypermetropia and myopia ?

Answer: Myopia is the near-sightedness and hypermetropia is the far-sightedness. The person who is suffering from both eye defects is advised to wear spectacles with a bi-focal lens which consists of both concave and convex lens. The upper portion would be a concave lens which rectifies the distant vision and lower portion is a convex lens which rectifies the near vision.

Question. John has undergone all medication including wearing spectacles, lens and laser treatment. None of the treatment helped him to recover his eyesight. What would be your suggestion to overcome his problem in his eyesight ?

Answer: Though all the treatment for recovering from his eye problems did not help him out, I would suggest him to opt for eye transplantation which would get his eyesight back to normal. In transplantation of eye, the entire diseased eye cannot be replaced. Only the diseased cornea can be replaced by the donated cornea.

Question. In today’s digital world, every human spends around a minimum eight hours with the digital electronic items which make their eyes to strain more and causes many eye problems. Still they undergo many exercises for their eyes during their working hours what would be your medical suggestion to reduce the stress and strain caused in the eyes ?

Answer: In addition to the exercise for the strained eyes, my medical suggestion would be the usage of the anti-glare lens in their spectacles which reduces the impact of blue light emitted from digital items and artificial lighting. This would reduce the stress and strain caused. But still the exercise for eyes in repeated time interval should also be regularly followed.

Paragraph/Table and Case Study Based Questions

White light is a mixture of seven colours is violet, indigo, blue, green, yellow, orange and red. Every colour has its own characteristic wavelength. Different colours with their wavelengths are given below is the table.
1. Red: 7900 Å
2. Orange: 6000Å
3. Yellow: 5800Å
4. Green: 5400Å
5. Blue: 4800Å
6. Indigo: 4500Å
7. Violet: 4000Å
The phenomenon of splitting white light into seven colors when it passes through a glass prism is called dispersion of white light.

Question. Name the phenomenon occurring in nature due to dispersion of light.
(i) Twinkling of stars
(ii) Rainbow
(iii) delayed sunrise
(iv) Red Sunrise

Answer: (ii)

Question. Light of two colours A and B pass through a glass prism. ‘A’ deviates more than B from its path of incidence. Which colour has a higher speed in the prism ?
(i) color A has higher speed than that of color B
(ii) Color B has higher speed than that of color A
(iii) both have same speed
(iv) None of the above

Answer: (ii)

Question. Choose the correct option.
(i) Each colour of light travels with same speeds in a given medium.
(ii) Each colour of light travels with different speeds in a given medium.
(iii) Only red colour of light travels with fast speed in a given medium.
(iv) all of the above.

Answer: (ii)

Question. The speed of light depends upon :
(i) frequency
(ii) wavelength
(iii) density
(iv) none of the above

Answer: (ii)