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## Monday, October 22, 2012

### Light, Shadows And Reflections Quest Time for class VI

Brain Teaser Quest Time For Class 6th Light, Shadows And Reflections

1. How can you determine the length of the shadow of an object?

Ans: We cannot correctly determine the length of the shadow of an object. The length of shadow depends on the angle at which light fall on a body and varies at different time of day. This principal helps us to make sun dial for calculating time.

2. How can you make sundial at home?

Ans: We take a pencil and place it into the whole of the empty spool of thread.This work as sundial.

Making the Sundial:

1. Using the pencil, poke a hole on the side of the paper / Styrofoam cup pproximately 2 inches below its top (rim).
2. Place the pebbles in the cup so to give it some weight and hold it upright.3. Cover the cup with the plastic lid.
4. Put the straw through the hole on the side of the cup and its lid while letting about half an inch of the straw stick out from the side.
4. Secure the straw to the cup by taping it down on the side.

3. How do you make a pinhole camera?

Ans: Take two rectangular boxes that fit into one another without leaving any gap.
Cut open one side of each box.

Make a small hole in the larger box at the centre of the closed end opposite the side that has been cut open.

Cut a square of side five centimetres in the smaller box in the closed end opposite the side that has been cut open. Cover this square with tracing paper.
Finally, slide the smaller box into the larger box, ensuring that the pinhole and the tracing paper are in line with one another, but at the opposite ends.

Slide the smaller box to adjust the focus so that you can capture the image of any object you want.

Look through the open face of the smaller box. you can see the image of the object and inverted on the screen.

4. Explain with the help of an activity that light travels in a straight line.

Ans: Place a candle at one corner of the room
Now look through the pipe, you can see the candle
Now bend the pipe and look. you cannot  see the candle
This shows that light travel in straight line called rectilinear propagation of light

5. What is meant by reflection of light ?

Ans: When light fall on smooth or rough surface return back after hitting these surface this phenomenon is called reflection of light

6. What types of image form in pinhole camera?

Ans: Inverted (upside-down)

7. Why is the image formed by a pinhole camera upside down?

Ans: It is because there is no refracting or reflecting optical element to change the path of the rays of light.

8. What happens if we place an opaque object in coloured light?

The colour of light will not affect the shadow, because shadow is the dark patch formed when an object obstructs the path of light

9. 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?

Ans: when the bird is flying very low close to the ground.

10. You are given a transparent glass sheet. Suggest any two ways to make it translucent without breaking it

Ans:
(i) By applying oil, grease, butter on it or pasting a butter paper on it.
(ii) Grinding (rubbing) the surface of the glass by any abrasive material.

11. Suggest a situation where we obtain more than one shadow of an object at a time.

Ans: We can obtain more than one shadow of an object if light from more than one source falls on it. [For example during a match being played in a stadium, multiple shadows of players are seen].

12. Three identical towels of red, blue and green colour are hanging on a clothes line in the sun. What would be the colour of shadows of these towels?

Ans: The colour of shadows of all three towels will be the same

13. Using a pinhole camera a student observes the image of two of his friends, standing in sunlight, wearing yellow and red shirt respectively. What will be the colours of the shirts in the image?

Ans: The colours of the image of the shirts will be the same as the colour of the shirt.

14. 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.

Ans: We can see the shadow of football lying on the ground because the ground acts as a screen for it. However, when the football is kicked high, the ground, which is acting as a screen is away from the football, hence no shadow of the football will be formed on the ground

15. . 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.

Ans: Possible reasons  (i) The screen away from the ball.
(ii) The beam of light from the torch is falling parallel to the screen on the ball.
(iii) The torch is kept away from the ball.

Lesson 11: Light, Shadows And Reflections.