11Animals and Plants Transportation in

1 LIGHT123 Light11 You might have seen a beam ofsunlight when it enters a roomthrough a narrow opening or a may have also seen beams of light fromthe headlamps of scooters, cars and enginesof trains [Fig. (a)]. Similarly, a beamof light can be seen from a torch. Some of(a) Rail engineFig. Beams of light(b) Light houseFig. Looking at a candle through a straight and a bent pipeyou may have seen a beam of searchlightfrom a light house or from an airporttower [Fig. (b)].What do these experiences suggest? LIGHT TRAVELS ALONG ASTRAIGHT LINEB oojho recalls an activity he performedin Class VI.

2 In that activity he looked(a)(b)Rationalised 2023-24 SCIENCE124 Fig. Reflection of objects in waterat a lighted candle first througha straight pipe and then througha bent pipe (Fig. ). Why wasBoojho not able to see the candleflame through a bent pipe?This activity showed thatlight travels along straight can we change the pathof light? Do you know, whathappens when light falls on apolished or a shiny surface? REFLECTION OF LIGHTOne way to change the directionof light is to let it fall on a shinysurface. For example, a shiningstainless steel plate or a shiningsteel spoon can change thedirection of light.

3 The surface ofwater can also act like a mirrorand change the path of you ever seen the reflectionof trees or buildings in water(Fig. )?Any polished or a shiny surface canact as a mirror. What happens whenlight falls on a mirror?You have learnt in Class VI that amirror changes the direction of light thatfalls on it. This change of direction by amirror is called reflection of light. Canyou recall the activity in which you gotthe light of a torch reflected from amirror? Let us perform a similar a torch. Cover its glass with a chartpaper which has three narrow slits asshown in Fig.

4 Spread a sheet ofPaheli remembers the story of the lion and therabbit from the Panchtantra, in which therabbit fooled the lion by showing him hisreflection in water (Fig. ).Fig. Reflection of the lion in waterRationalised 2023-24 LIGHT125chart paper on a smooth wooden a plane mirror strip vertically on thechart paper (Fig. ). Now direct thebeam of light on the mirror from thetorch with slits. Place the torch in sucha way that its light is seen along thechart paper on the board. Now adjustits position so that the light from thetorch strikes the plane mirror at anangle (Fig.)

5 Does the mirror change the directionof light that falls on it? Now move thetorch slightly to either side. Do you findany change in the direction of reflectedlight?Look into the mirror along thedirection of the reflected light. Do yousee the slits in the mirror? This is theimage of the activity shows how light getsreflected from a plane us play around with the imagesformed in mirrors and know a little moreabout Image of a candle in a plane mirrorFig. Reflection of light from a mirrorPaheli wants to know, whatmakes things visible to us?Boojho thinks that objects arevisible only when light reflectedfrom them reaches our eyes.

6 Doyou agree with him?CAUTIONH andle the lighted candle with is better if this activity is performedin the presence of a teacher or an a lighted candle in front of a planemirror. Try to see the flame of the candlein the mirror. It appears as if a similarcandle is placed behind the mirror. Thecandle, which appears behind themirror, is the image of the candle formedby the mirror (Fig. ). The candleitself is the move the candle to differentpositions in front of the mirror. Observethe image in each 2023-24 SCIENCE126cannot be obtained on the screen ineither about the distance of the imagefrom mirror?

7 Let us perform a chess board. If a chess board isnot available, draw on a chart paper 64(8 8) squares of equal size. Draw a thickline in the middle of the paper. Fix aplane mirror vertically on this line. Placeany small object, such as a pencilsharpner, at the boundary of the thirdsquare counting from the mirror(Fig. ). Note the position of theimage. Now shift the object to theboundary of the fourth square. Againnote the position of the image. Did youfind any relation between the distanceof the image from the mirror and that ofthe object in front of it?

8 Was the image upright in each case?Did the flame appear on top of the candleas in the object? Such an image is callederect. An image formed by a planemirror is erect and of the same size asthe place a vertical screen behindthe mirror. Try to obtain the image ofthe candle on this screen. Can you getthe image on the screen? Now place thescreen in front of the mirror. Can youget the image on the screen now? Youwill find that the image of the candleBoojho noted in his notebook: Isit not surprising that my image isof the same size as me whetherthe mirror is small or large?

9 Fig. Locating image in a plane mirrorPaheli made a note in her notebook:In a plane mirror the image isformed behind the mirror. It is erect,of the same size and is at the samedistance from the mirror as theobject is in front of will find that the imageis at the same distance behindthe mirror as the object is in frontof it. Now verify this by placingthe object anywhere on the 2023-24 LIGHT127 Fig. Left hand appears on the right sidein the imageFig. An ambulancemirror. How does it appear in themirror? RIGHT OR LEFT!When you see your image in a planemirror, is it exactly like you?

10 Have youever noticed that there is one interestingdifference between you and your imagein a mirror? Let us find in front of a plane mirror and lookat your image. Raise your left hand does your image raise(Fig. )? Now touch your right ear does your hand touch in yourimage? Observe carefully. You will findthat in the mirror the right appears left and the left appears right . Note thatonly sides are interchanged; the imagedoes not appear upside write down your name on a pieceof paper and hold it in front of a planeBoojho saw an ambulance onthe road.