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GURUKUL CENTRAL ACADEMY, CH.- 12. LIGHT, SHADOWS AND, REFLECTIONS, WORKSHEET-1, Refer text book, WORKSHEET-2, E., F., , 1. Opaque 2. Transparent 3. translucent, No, because there would be no sun., , WORKSHEET-3, 1., 2., 3., , The person will see torch light, The person will not be able to see light, Light travels in a straight line, , TEXTBOOK EXERCISES, Page 134 Try These, 1. False, 2. True, , 3. True, , 4. True, , 5. True, , Page 139 Try These, 1. source 2. Thomas Edison 3. opaque 4. beam 5. black

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GURUKUL CENTRAL ACADEMY, EXERCISES, A., , 1. a. 2. a. 3. a. 4. a. 5. d. 6. a. 7. d. 8. x. 9. b. 10. b., , B. 1. c., , 2. d., , 3. a., , 4. e., , 5. b., , C., , 1. Light creates a sensation of vision., 2. Light travels in a straight line., 3. Opaque objects do not allow any light to pass through them., 4. A lunar eclipse occurs only on a full moon day., 5. Umbra is the region of complete darkness., 6. A shadow is always black., , D., , 1. A form of energy, 2. Yes, 3. No, 4. Represented by a line with an arrow head to show direction, 5. No, 6. it bounces back, 7. No, , E., , 1. Light enables us to see things., 2., , Materials that allow light to pass through them easily are called, transparent materials., Materials that allow light to pass through them only partially are, called translucent materials., Materials that do not allow light to pass through them at all are, called opaque materials.

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GURUKUL CENTRAL ACADEMY, 3., , Because they reflect the light falling on them., , 4., , (a) Refer Table 12.1 from page 142., (b). Luminous Objects:, 1. Objects that emit light are called luminous objects., 2. Sun, stars, tube light etc. are luminous objects., Non-luminous Objects:, 1. Objects that do not emit light on their own are called nonluminous objects., 2. Moon, chair, table etc. are non-luminous objects., , F., , 5., , A shadow has two regions: umbra and penumbra, Umbra: It is the region of complete darkness. No light rays, reach here., Penumbra: It is the region of partial darkness which surrounds, the umbra region. Some light rays reach here., , 6., , The conditions which are essential for the formation of a shadow, are as follows:, • Presence of a source of light., • An opaque object to obstruct the path of light., • A screen or surface behind the opaque object on which, shadow will form., , 1. Refer Experiment 1, page 136., 2., , A shadow depends upon the source of light, the shape of the, opaque object and the screen or surface on which it forms.

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GURUKUL CENTRAL ACADEMY, 3., , When the moon is in position X, no light from the sun falls on it., This is called a total lunar eclipse. In position Y, it is a partial, lunar eclipse. When a lunar eclipse occurs, the bright side of the, moon faces the earth. Therefore, a lunar eclipse occurs on a full, moon day., Refer diagram 12.15 from page 139., , 4., , Construction: Take a cubical carton closed at all the sides except, one. Cover the open side with a butter paper sheet using cello, tape. This is the screen. Make a tiny hole on the side opposite to, the butter paper sheet, and cover it using a black tape. Pierce the tape with a very fine,, sharp needle. The camera is ready!, Working: Place the pinhole camera in front of an object as shown, in the Fig. 12.9. The light ray from the object travels into the, pinhole from two points P and Q in a straight line and forms small, and an inverted image of the object R and S on the screen. When, the object is moved away towards the hole, the size of the image, changes., Refer diagram 12.9 from page 137., , 5., , The phenomenon of bouncing back of light rays after striking the, surface of an object into the same medium from where it came, initially is termed as reflection of light., When the light beams fall on a rough surface like a table or almirah, the direction of their reflection varies because of the irregular, surface. This is called diffused reflection.

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GURUKUL CENTRAL ACADEMY, 6., , G., , Image formed by a plane mirror has the following characteristics, • Image is formed as far behind the mirror as the object, is in front of it., • The size of the image is the same as that of the object., • The image is laterally inverted that is the right appears, left and vice-versa., • The image only appears to be there but is actually not there. We can’t, take such type of image on a screen and is referred to as a virtual, image. You would have observed that if you moved backwards then, the image too moved backwards, though there is no space in the, mirror. This shows that the image is not real but virtual., • Image is erect in nature., , 1. Because it reflects the light of the sun falling on it., 2. Because opaque objects do not allow the light to pass through, them. Since light travels in a straight line and cannot bend around, the opaque objects, a dark region called shadow is obtained behind, them.