Light

Light travels in straight lines, so we cannot see a flame through a bent pipe. When light falls on a shiny surface like a mirror, it changes direction; this is reflection. The image in a plane mirror is erect, the same size as the object, and as far behind the mirror as the object is in front. It is also laterally inverted; this is why AMBULANCE is written in reverse on ambulances. An image that can be obtained on a screen is real, and one that cannot is virtual. Curved mirrors and lenses form different images. A concave mirror can form real, inverted images on a screen and enlarged erect images of nearby objects, so dentists use it. A convex mirror always forms an erect, smaller image and is used as a rear view mirror. A convex lens works as a magnifying glass, while a concave lens always gives an erect, smaller image. White sunlight is made of seven colours, seen in a rainbow, through a prism and with Newton's disc.

Detailed Worksheet: Light Section A - Definitions (10 marks) 1. What is meant by rectilinear propagation of light? Give one evidence. (2 marks) 2. Define reflection of light. Name the surface that reflects light best. (2 marks) 3. Distinguish between a real image and a virtual image. (2 marks) 4. What is lateral inversion? Give an example. (2 marks) 5. What are spherical mirrors? Name their two types. (2 marks) Section B - Calculations and Applications (15 marks) 6. A boy stands 2 m in front of a plane mirror. (i) How far is his image from the mirror? (ii) How far is the image from the boy? (iii) If he walks 0.5 m towards the mirror, what is the new distance between him and his image? (3 marks) 7. Write the letters of the word "LIGHT" as seen in a plane mirror. Which capital letters among A, B, H, M, O, P, T look the same in a mirror? (3 marks) 8. State the type of mirror or lens used in (i) the rear view mirror of a scooter (ii) a dentist's mirror (iii) a magnifying glass (iv) a torch reflector (v) a dressing table mirror (vi) shaving mirror. (3 marks) 9. Compare a convex lens and a concave lens: shape, image formed, one use each. (3 marks) 10. What are the seven colours of sunlight in order? How can you show that white light is made of these colours using a glass prism? (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram showing the image of a candle formed by a plane mirror, marking the object distance and image distance. (4 marks) 12. Draw the shapes of a concave mirror, a convex mirror, a convex lens and a concave lens, labelling the reflecting side of the mirrors. (3 marks) 13. Draw a labelled Newton's colour disc and explain why it appears whitish when rotated fast. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Boojho placed a candle in front of a concave mirror and moved a screen to catch its image. (i) What kind of image did he get when the candle was far away? (ii) What happened when the candle was very close to the mirror? (iii) Could he get an image on the screen with a convex mirror? (iv) Why are concave mirrors used in torches and headlights? (5 marks) 15. Paheli saw "ECNALUBMA" written on the front of a vehicle. (i) Why is it written like this? (ii) How will the driver ahead read it? (iii) What property of plane mirrors is used? (iv) Write your name as it would appear in a mirror. (5 marks) 16. A rainbow is seen after rain when the Sun is behind the observer. (i) Why does it form? (ii) In what order do the colours appear? (iii) How is a rainbow similar to what a prism does? (iv) Describe an activity to make a rainbow at home. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Never look at the Sun directly or through a lens, and draw ray diagrams with a sharp pencil and ruler.