Light ASSIGNMENT 1. Fill in the blank spaces by choosing the correct words from the list given below : List : compound microscope, yellow, telescope, alter, vitreous humour, time, photographic camera, refraction, convex lens, dispersion. (a) Shutter is a device in photographic camera, which controls the... for which light enters the camera. (b)... is the phenomenon of splitting white light into seven colours. (c)... is a device used for seeing germs and bacteria. (d)... is a device used for seeing heavenly bodies. (e)... is a jelly like fluid found within the eye ball. (f)... is a device used for obtaining permanent images of objects. (g) A single... is used as magnifying glass. (h) Ciliary muscles... the focal length of crystalline lens. (i)... spot in eye is highly sensitive to light. (j)... is the phenomenon, due to which light deviates from its path, while travelling from one medium to another medium. 2. Statements given below are incorrect. Write the correct statements. (a) The phenomenon due to which light deviates from its path, is called reflection. (b) The angle of incidence, the angle of refraction and the normal lie in different planes, during refraction. (c) When a ray of light travels from denser to rarer medium, it bends towards the normal. (d) The ratio between the velocity of light in glass to velocity of light in vacuum, is called refractive index of glass. (e) When the refraction of light takes place through prism, then sum of the angle of incidence and angle of deviation is equal to sum of angle of prism and angle of emergence. 1
(f) Yellow spot is a small area on the choroid, which is highly sensitive to light. (g) A telescope having an objective and an eye lens, can be used for seeing all kinds of objects. 3. Write True or False in front of the following statements given below. (a) In case of photographic camera, the object is beyond 2F of the convex lens. (b) In case of simple microscope, the object is always between F and O of the convex lens. (c) Convex lens always forms a real and inverted image. (d) Concave lens always forms a virtual and enlarged image. (e) A simple microscope is used for studying simple biological specimens. (f) The bottom of water tank filled with water appears raised due to reflection. (g) Iris controls the focal length of crystalline lens. (h) A prism can break white light into seven colours. (i) Dispersion is the phenomenon, when white light suffers reflection. (j) A ray travelling from rarer to denser medium, bends towards the normal. 4. Match the statements in column A, with those in column B. Column A Column B (a) The phenomenon due to which bottom of tank filled with water appears raised. (b) The phenomenon of splitting up of white light. (c) A device used for seeing germs and bacteria. (d) A device used for seeing heavenly bodies. (e) A device used for obtaining permanent image of an object. (f) A lens used as magnifying glass. Vitreous humour Refraction Camera Compound microscope Convex lens Telescope (g) A part of eye, which alters focal length of crystalline lens. (h) A highly sensitive part on the retina of eye. (i) A jelly like fluid found in eye ball. Shutter Ciliary muscles Yellow spot ( j) A device in camera, which controls the time of exposure. Dispersion 2
5. Tick ( ) the most appropriate answer. (a) A ray of light travelling obliquely from a denser to a rarer medium : (i) bends towards the normal (ii) bends away from the normal (iii) does not deviate from its path (iv) none of these (b) During the dispersion of light, the least dispersed colour is : (i) violet (ii) green (iii) red (iv) yellow (c) When a coin placed in a bowl of water is seen from above, it appears : (i) raised from its actual position (ii) below its actual position (iii) at the same position (iv) none of these (d) In a compound microscope, the objective lens is of : (i) smaller focal length than eye lens (ii) larger focal length than eye lens (iii) same focal length as eye lens (iv) none of these (e) If v c is the speed of light in vacuum and v m is the speed of light in a given medium, then refractive index of medium is : (i) v m /v c (ii) v c /v m (iii) v m v c (iv) none of these (f) The phenomenon of splitting white light into seven colours, is called : (i) reflection (ii) refraction (iii) refractive index (iv) dispersion (g) A defect in the human eye, in which a person can see clearly the nearby objects, but cannot see the far-off objects clearly is called : (i) myopia (ii) presbyopia (iii) hypermetropia (iv) none of these (h) A part of the eye, which helps in changing the focal length of crystalline lens is : (i) iris (ii) aqueous humour (iii) cornea (iv) ciliary muscles (i) A real, inverted and highly enlarged image is formed by a convex lens when the object is : (i) beyond 2F (ii) F and 2F (iii) at 2F (iv) at F (j) The velocity of light in vacuum is : (i) 3 10 8 ms 1 (ii) 5 10 8 ms 1 (iii) 3 10 5 ms 1 (iv) 6 10 8 ms 1 3
6. Find the odd one out. Give a reason for your choice. (a) yellow spot, dispersion, blind spot, cornea. (b) myopia, hypermetropia, hypertension, presbyopia. (c) refractive index, angle of incidence, angle of reflection, refracted ray. 7. (a) What do you understand by the term refraction of light? (b) Diagrams given below, show a ray of light moving from one optical medium to another optical medium. Complete the course of rays in each case. 8. Diagram alongside, shows a stick immersed obliquely in water. By drawing two rays diagram, show how the eye sees the image of stick. Briefly explain your answer. 9. State laws of refraction. 10. Diagram alongside shows a glass slab and the incident ray AB and emergent ray CD. Complete and label the diagram and define the following : (a) Refracted ray (b) Angle of incidence (c) Angle of refraction (d) Angle of emergence 4
11. (a) Diagram alongside shows an equilateral glass prism, such that a ray AB is incident on it. Trace the path of the ray through glass prism and label clearly on the diagram, (i) angle of incidence, (ii) angle of emergence, (iii) angle of deviation, (iv) angle of prism. (b) State a relation between the angles mentioned in 11(a). 12. Diagram alongside shows a coin placed in a beaker filled with water. By drawing two rays diagram, show how the eye sees the image of the coin. Briefly explain your answer. 13. What do you understand by the following terms? (a) Lens (b) Convex lens (c) Concave lens (d) Principal axis (e) Optical centre (f) Focal length for convex lens (g) Focal length for concave lens 14. (a) Define the following terms : (i) Dispersion of light (ii) Spectrum (b) Draw a neat and labelled diagram for the formation of spectrum. 15. Complete the path of ray AB in the diagrams given below : 5
16. (a) The above diagram shows an object AB, situated in front of a convex lens beyond 2F. By drawing a two rays diagram, show the formation of image and state its three characteristics. 6
(b) Name an optical device which uses the above principle. 17. Diagram given below shows an object AB in front of a concave lens at F. By drawing two rays diagram, show the formation of image and state its three characteristics. 18. (a) Give four uses of convex lens. (b) Give two uses of concave lens : 19. Fill in the blank spaces : Position of object Position of image Kind of lens Nature of image Object is between F and 2F Convex Object is beyond 2F Real, inverted and diminished. Object is between infinity and optical Concave centre Infinity Real, inverted, highly magnified. Object is between Convex F and O Concave Virtual, erect and diminished to a point. 20. Fill in the blank spaces by choosing correct words from the list given below : List : lens, deviation, emergent, refraction, rarer, deviates, towards. (a) A ray of light while travelling from one optical medium to another optical medium... from its path. This phenomenon is called... of light. 7
(b) A ray of light while travelling from optically... medium to optically denser medium, deviates... normal. (c) The angle of... is the angle between the incident ray and... ray when the ray of light passes through glass prism. (d) A piece of transparent material bounded by one or two spherical surfaces, is called... 21. (a) Where should an object be placed in front of a convex lens, so that it acts as a magnifying glass? (b) State three characteristics of the image formed by a magnifying glass. (c) State any three uses of magnifying glass. 22. Answer the following questions regarding telescope. (a) What telescope is employed for? (b) Name the lens of the telescope which faces towards (i) object (ii) eye (c) Which of the two lenses used in telescope, has more focal length? (d) Why are the tubes carrying the lenses of the telescope blackened from inside? (e) State three characteristic of the image formed by a telescope. 23. Answer the following questions regarding the compound microscope. (a) Which, amongst the two lens used in it, has a smaller focal length? (b) Does the lens named in (a) face towards object or the eye? (c) Where should be eye lens with respect to the image formed by the objective lens? (d) State three characteristics of the image formed by a compound microscope. 24. Draw a simplified diagram of human eye showing (i) crystalline lens, (ii) ciliary muscles, (iii) retina, (iv) vitreous humour. 25. State the functions of the following parts of human eye : (a) Cornea (b) Retina (c) Yellow spot (d) Ciliary muscles (e) Iris 8
26. (a) What do you understand by the term accommodation of eye? (b) How does the human eye see nearer objects? (c) How does the human eye see far-off objects? (d) What do you understand by the term defective eye? 27. (a) What do you understand by the term myopia? (b) State two causes of myopia. 28. (a) What do you understand by the term hypermetropia? (b) State two causes of hypermetropia. 29. (a) Draw a neat diagram for photographic camera. (b) State the functions of diaphragm in photographic camera. (c) State the functions of shutter in photographic camera. 9