NCERT Exemplar Problems Class 6 Science – Light
Observe the picture given in the figure carefully.
A patch of light is obtained at B when the torch is lighted as shown. Which of the following is kept at position A to get this patch of light?
(a) A wooden board (b) A glass sheet
(c) A mirror (d) A sheet of white paper
(c) A mirror is kept at position A to get a patch of light because only a mirror can change the direction of light that falls on it, i.e. causes reflection.
Four students A, B, C and D looked through pipes of different shapes to see a candle flame as shown in figure.
Who will be able to see the candle flame clearly?
(a) A (b) B (c) C (d) D
(d) Student D will be able to see the candle flame clearly because light travels along a straight line. However, students A, B and C will not be able to see the flame clearly because the tubes are not straight.
A student observes a tree given in figure through a pinhole camera. Which of the diagrams given in figure (a) to (d) depicts the image seen by her correctly?
(d) Option (d) is the correct image seen by her because a pinhole camera always forms upside down (i.e. inverted) image.
Which of the following is/are not always necessary to observe a shadow?
(a) Sun (b) Screen (c) Source of light (d) Opaque object
(a) Sun is not always necessary to observe a shadow because any source of light, an opaque object and a screen are just necessary enough to see a shadow.
Paheli observed the shadow of a tree at 8:00 am, 12:00 noon and 3:00 pm. Which of the following statements is closest to her observation about the shape and size of the shadow?
(a) The shape of the shadow of the tree changes but the size remains the same.
(b) The size of the shadow of the tree changes but the shape remains the same.
(c) Both the size and shape of the shadow of the tree changes.
(d) Neither the shape nor the size of the shadow changes.
(c) Both the size and shape of the shadow of the tree will be changed because at 8:00 am and 3:00 pm, the lengths of the shadows of tree will be longer than its actual length and point to the West and the East directions, respectively. However, at 12:00 noon, the sun will be high in the sky just above the tree, so the shadow of tree will be short.
Which of the following can never form a circular shadow?
(a) A ball (b) A flat disc
(c) A shoe box (d) An ice-cream cone
(c) A shoe box can never form a circular shadow because in. any condition it does not have a circular shape. However, a ball, a flat disc and the base of ice-cream cone can form a circular shadow.
Two students while sitting across a table looked down onto its top surface. They noticed that they could see their own and each other’s image. The table top is likely to be made of
(a) unpolished wood (b) red stone
(c) glass sheet (d) wood top covered with cloth
(c) The table top must be made of glass sheet because only a glass sheet can show the images of both the students, which can be seen by both of them.
Very Short Answer Type Questions
You have 3 opaque strips with very small holes of different shapes as shown in figure. If you obtain an image of the sun on a wall through these holes, will the image formed by these holes be the same or different?
A small circular image of the sun will be obtained in all the three cases because the holes will act as a pinhole camera, whatever be their shapes. Also, as the light moves in a straight path, therefore the image of the sun will remain same.
Observe the picture given in figure. A sheet of some material is placed at position P, still the patch of light is obtained on the screen. What is the type of material of this sheet?
A sheet of transparent material is placed at position P because only a transparent material allows light to pass through it undisturbed and therefore, the patch of light is obtained at the same place on the screen.
Three torches A, B and C shown in figure are switched ON one by one. The light from which of the torch will not form a shadow of the ball on the screen?
The light from the torch C will not form a shadow on the screen because light travels in a straight path and forms the shadow on the same path from which it is coming.
Look at the given figure.
Will there be any difference in the shadow formed on the screen A and B?
No, there will not be any difference because the length and breadth of an object are same in both the cases.
Short Answer Type Questions
Correct the following statements.
(a) The colour of the shadow of an object depends on its colour.
(b) Transparent objects allow light to pass through them partially.
(a) The colour of the shadow of an object does not depend on its colour. It is always black irrespective of any coloured object.
(b) Transparent objects allow most of the light to pass through them or translucent objects allow light to pass through them partially.
Suggest a situation where we obtain more than one shadow of an object at a time.
More than one shadow or multiple shadows of an object can be obtained by using multiple sources of light, i.e. during a night match being played in a stadium, multiple shadows of players are seen due to flood (stadium) lights in the stadium.
On a sunny day, does a bird or an aeroplane flying high in the sky cast its shadow on the ground? Under what circumstances, can we see their shadow on the ground?
No, they do not cast any shadow on the ground because they are very high in the sky. They can cast shadow only if they are at some lower height, i.e. if they are near to the ground, we can see their shadows. \
You are given a transparent glass sheet. Suggest any two ways to make it translucent without breaking it.
Transparent glass sheet can be made translucent by two ways:
(i) By rubbing it on the ground and making it rough.
(ii) By applying oil, grease or butter on it.
A torch is placed at two different positions A and B one by one as shown in figure.
The shape of the shadow obtained in two positions is shown in the given figure.
Match the position of the torch and shape of the shadow of the ball.
Position A of the torch will form the shadow (a) and position B of the torch will form the shadow (b) of the football. Here, difference in shapes of shadows (a) and (b) of ball is due to the difference in the positions A and B of torch from the ball.
The bigger shape of shadow (a) than shadow (b) of ball is formed only because the screen, torch in position A and ball are in same straight line.
A student covered a torch with red cellophone sheet to obtain red light. Using the red light, she obtains a shadow of an opaque object. She repeats this activity with green and blue lights. Will the colour of the light affect the shadow? Explain.
Shadow is just an absence of light at that place. Shadow is not affected by the colours of the object because the amount of light preventing to pass will remain same.
The shadow is affected by the shape of the object only. If the object is large, the shadow will be large and vice-versa.
Is air around us always transparent? Discuss.
We can see the objects through air clearly, means we can observe all the objects in their original shapes and sizes without any disturbance, it means the environment around us which is just air, must be transparent.
But when thick smoke, thick clouds, etc., are present in the air, it does not remain transparent. .
Three identical towels of red, blue and green colour are hanging on a clothe’s line in the sun. What woutd be the colour of shadows of these towels?
Shadow of an object does not change on changing its colour. Shadow will always show the absence of light at that place. So, the colour of shadow will remain same in all the cases. Thus, the shadows of all the towels are black in colour.
Using a pinhole camera, a student observes the image of two of his friends, standing in sunlight, wearing yellow and red shirts, respectively. What will be the colours of the shirts in the image?
Colours of the shirts will remain same. We see them on the screen because pinhole camera forms the image of the object having same colour but upside down.
So, yellow shirt will form yellow image and red shirt will form red image.
In given figure, a flower made of thick coloured paper has been pasted on the transparent glass sheet. What will be the shape and colour of shadow seen on the screen?
The shape of the flower on the screen will be the same as that of the flower but the shadow of flower is of black colour.
Long Answer Type Questions
A football match is being played at night in a stadium with flood lights ON. You can see the shadow of a football kept at the ground but cannot see its shadow when it is kicked high in the air. Explain.
The shadow of an object cannot be caught if the screen and the object are very far from each other. This is the same case. Here, also the shadow of the football cannot be seen on the ground (which acts as a screen) when it is kicked high in the air.
This happens because if we take the object away and away from the screen, the shadow becomes smaller and smaller in size and a time comes when it totally disappears from the screen.
A student had a ball, a screen and a torch in working condition. He tried to form a shadow of the ball on the screen by placing them at different positions. Sometimes, the shadow was not obtained. Explain.
Sometimes, the shadow of the object (ball) may not be formed because of improper arrangement of source of light (torch), object and screen. It may be due to the following reasons— (a) The screen from the ball, (b) The direction of beam of light from the torch falling on the ball, is parallel to the screen, (c) The torch is kept away from the ball.
An accurate shadow of ball will be formed only if screen, torch and ball are in the same straight line (as shown in figure).
A sheet of plywood, a piece of muslin cloth and that of a transparent glass, all of the same size and shape were placed at A one by one in the arrangement shown in figure. Will the shadow be formed in each case? If yes, then how will the shadow on the screen be different in each case? Give reasons for your answer.
Yes, the shadow will be formed in each case but in all the cases, the darkness of the shadow will be different.
(i) Most of the light in case of transparent sheet of glass will pass through the glass. So, the darkness of shadow will be very low.
(ii) Most of the light in case of muslin cloth will be reflected. So, the shadow will be darker than the transparent sheet of glass.
(iii) While in case of plywood, all the light would be stopped completely by the plywood. So, the darkness strength will be highest in this case.