Class 6 Light, Shadows-Reflections
Short Answer Questions
1. What is lateral inversion?
2. State any one observation from everyday life which shows that light travels in straight line.
3. Distinguish between a solar and a lunar eclipse.
4. Which of the following are the sources of light? The book, tube light, the moon, the sun, stars, planets, meteor, table, chair, electric bulb.
5. Distinguish between the natural source of light and artificial source of light.
6. What are the characteristics of a shadow?
7. What is the difference between an image and a shadow?
8. What are the things required to observe a shadow?
Ans:
1. If we stand in front of a plane mirror, we see the image of our body in it. Though our image appears to be just as we are but there is a peculiar difference in it. In the image, the left-hand side pocket of our shirt will appear on the right-hand side. Our right eye will appear as the left eye in our image. Our right and the left hand will appear as the left and right hand respectively. It means that the side of the image is inverted, i.e., opposite to that of the object formed by a plane mirror which is called as lateral inversion.
2. Light travelling from the sun to the earth is an observation that shows light travels in a straight line.
3. When the earth comes between the moon and the sun, the earth’s shadow falls on the moon. This is called a lunar eclipse. When the moon comes between the sun and the earth, the moon’s shadow falls on the earth. This is called a solar eclipse.
4. Tube light, moon, sun, star, electric bulb
5. The source of light which occur naturally are called the natural source of light, e.g., the sun, stars and glow worms are some natural sources of light.
Sources which are made by man artificially are called the man-made source of light. For example, electric bulb, tube light, kerosene oil, candle, CFL, fluorescent lamp.
6. The nature of shadow depends on the nature of the object which blocks the light.
• The size of the shadow depends on the size of the source of light and object and also on the distance between the source of light and the object, the wall or the screen.
• A transparent object does not stop light completely. Therefore, it casts a weak shadow.
• A translucent object stops light only partially. Therefore, it casts a weak shadow.
• An opaque object stops the light completely. Therefore, it casts a dark shadow.
• The shadow is always formed in the opposite direction of the source of light.
• The sharpness of the shadow depends on the size of the light source.
• The shape of the shadow is usually similar to the outline of the objects which block the light. Hence, we can identify an object from the shadow.
• When the source of light or the object moves, the shadow also shifts accordingly.
7. A shadow is a dark space (shade) formed behind an opaque object when it blocks light from any source. When we look into a mirror held in our hand, we see our face. What we see in the mirror is actually a reflection of our face and it is called the image of our face.
8. The things required to observe a shadow are a source of light, object and screen.
Long Answer Questions
1. Distinguish between a parallel, a convergent and a divergent beam of light. Illustrate with examples.
2. Describe an experiment to demonstrate rectilinear propagation of light.
3. What is meant by (a) luminous objects and (b) non-luminous objects? Name any three luminous objects and three non-luminous objects. State whether the moon is a luminous object or a non-luminous object.
Ans:
1. A beam of light is parallel when the rays of light are parallel to each other, i.e is the distance between the rays remains the same.
• A beam of light is convergent when the rays of light meet at a point.
• A beam of light is divergent when the rays of light spread out from a point. The distance between the rays goes on increasing.
2. To show that light travels in a straight line Materials Required: A piece of rubber tube and a candle
Procedure: Fix a lighted candle on a table, stretch a narrow rubber tube straight and look through it at the flame. Do you see light coming from the flame? The light from the flame is visible. Now coil the rubber tube and look through it at the flame. Do you see the light coming from the flame? The light coming from the flame is not seen.
Conclusion: This experiment shows that light travels in straight line.
3. The object that gives out its own light is called a luminous object. Sun, stars and a burning candle are examples of luminous objects. Objects that do not give out their own light are called non-luminous objects. A pencil, clothes, paper and the wall are some common examples of non-luminous objects. Moon is a non-luminous object. It does not have the light of its own. It shines because of the light of the sun falling on it.
HOTS
1. How do we get moonlight when a moon is a non-luminous object.
2. What happens to the shadow formed on a screen when
(a) the distance between the source of light and the object increases.
(b) the distance between the object and the screen decreases.
3. What will be the colour of a shadow formed in red light?
Ans:
1. Moon is a non-luminous object. It does not have the light of its own. It shines because of the light of the sun falling on it.
2. (a) The shadow becomes small.
(b) The shadow becomes big.
3. The shadow will be black in colour.