Q.1. The sky appears dark instead of blue to an astronaut. State its reason.
Answer. The sky appears dark to the astronaut as scattering does not take place at very high altitude due to the absence of atmosphere.
Q.2. Which phenomenon is responsible for making the path of light visible?
Answer. Tyndall effect.
Q.3. State one function of iris in human eye.
Answer. Iris controls the size of pupil.
Q.4. State one function of pupil in human eye.
Answer. Pupil regulates and controls the amount of light entering the eye.
Q.5. State one role of ciliary muscles in the human eye.
Answer. Ciliary muscles help the eye lens to focus the image of an object on the retina by increasing or decreasing the curvature of eye lens.
Q.6. What will be the colour of the sky, when it is observed from a place in the absence of any
Answer. Sky appears dark.
Reason: In the absence of atmosphere, there would have been no scattering of sunlight at all.
Q.7. State one function of the crystalline lens in the human eye.
Answer. Crystalline (eye) lens forms a real and inverted image of the object on the retina.
Q.8. In which direction, the near point of hypermetropic eye is shifted from the normal near
Answer. The near point of hypermetropic eye is shifted farther away from the normal near point.
Q.9. State two properties of the image formed by the eye lens on the retina.
Answer. (a) Image on the retina is real and inverted. (b) Diminished in size.
Q.10. State one function of cornea in human eye.
Answer. Cornea provides the refraction of light rays entering the eye.
Q.11. Why does the sun appear reddish at sunrise?
Answer. At sunrise, the sun looks almost reddish because only red colour ( λb < λr), which is least scattered is received by our eye and appears to come from the sun. Hence, the appearance of sun at sunrise, near the horizon may look almost reddish.
Q.12. What is Tyndall effect?
Answer. The phenomenon of scattering of light by the colloidal particles is called Tyndall effect.
Q.13. Give an example of optical phenomena which occurs in nature due to atmospheric refraction.
Answer. Twinkling of stars.
Q.14. Give an example of a phenomenon where Tyndall effect can be observed.
Answer. When a fine beam of sunlight enters a room containing suspended particles of dust, the path of the beam of light is visible. It is due to the scattering of light (Tyndall effect).
Q.15. Name the type of particles which acts as a prism in the formation of rainbow in the sky.
Answer. Water droplets present in the atmosphere.
Q.16. What is the cause of dispersion of white light on passing through a prism?
Answer. The refractive index of the material of a prism is different for different colours of light as different colours have different speeds in the material of a prism. Also, prism has non-parallel surfaces.
Q.17. In a human eye, name the following parts:
(a) a thin membrane which allows light to enter the eye.
(b) the muscles which help in changing the focal length of eye lens.
Answer. (a) Cornea
(b) Ciliary muscles
Q.18. Name the atmospheric phenomenon due to which the sun can be seen above the horizon about two minutes before actual sunrise.
Answer. Atmospheric refraction.
Q.19. Name the component of eye that is responsible for the adjustment of eye lens?
Answer. Ciliary muscles
Q.20. Why is red colour selected for danger signal lights?
Answer. Wavelength of red colour is more and so, it is least scattered. It can be easily seen through a large distance.
Q.21. A person is advised to wear spectacles with convex lenses. What type of defect of vision is he suffering from?
Answer. Hypermetropia or far-sightedness.
Q.22. Name the part of our eyes that helps us to focus near and distant objects in quick succession.
Answer. Ciliary muscles help in changing the focal length of the eye lens.
Q.23. A person can comfortably read a book but finds it difficult to read the number on a bus parked 5 m away from him. Name the type of defect of vision he is suffering from. Which type of lens should he use in his spectacles to correct his vision?
Answer. Myopia or short-sightedness. Concave lens should be used to correct his vision.
Q.24. A person is advised to wear spectacles with concave lenses. What type of defect of vision is he suffering from?
Answer. Myopia or short-sightedness.
Q.25. Why do different components of white light deviate through different angles when passing through a triangular glass prism?
Answer. Due to change in refractive index offered by the medium.
Q.26. A person suffering from an eye defect uses lenses of power 1D. Name the defect he is suffering from and the nature of lens used.
Answer. Hypermetropia; convex lens.