CBSE Class 6 Science Light Shadows And Reflections Worksheet Set A

Learning Objectives
1. Introduction
2. Sources of light - Natural and Artificial
3. Luminious and Non-luminous objects
4. Transparent, translucent and opaque objects
5. Rectilinear propagation of light
6. Pinhole camera
7. Shadows and Images
8. Solar and Lunar eclipses
9. Reflection of light

INTRODUCTION
We see the colourful and beautiful world around us. Light helps us to see things around us. We cannot see light but light creates sensation of vision. We detect light with our eyes. Light is a form of energy.

SOURCES OF LIGHT – NATURAL AND ARTIFICIAL
The objects that givse out light are called sources of light.

There are two types of sources of light
1. Natural sources : Sun and stars are natural sources of light.
2. Man-made (or artificial sources) : Electric bulb, glowing tube-light, fire, burning candle etc are all man-made sources of light.
Do You Know : objects give off light at different wave- length which is invisible. These materials are called fluorescent materials.

LUMINOUS AND NON-LUMINOUS OBJECTS
The objects which emit their own light are called luminous objects. For e.g. Sun, stars, torch, fire, flame of a candle are luminous objects. We can see luminous objects due to the light emitted by them.
The objects which do not emit their own light are called non-luminous objects.
For e.g. Earth, table, chair, flowers etc., are non-luminous objects. Non-luminous objects are visible because of the light falling on them from luminous objects.

TRANSPARENT, TRANSLUCENT AND OPAQUE OBJECTS
An object which allows most of the light to pass through it is called as transparent object. For e.g. Air, glass, water, etc. An object which allows only a part of the light to pass through it is called as translucent object. For e.g., Milky white plastic, frosted glass etc. An object which does not allow light to pass through it is called as opaque object. For e.g., wood, cement, metal sheet etc.
Do You Know : Ultraviolet rays can go through trans- lucent objects. Due to this a person behind this object can get a sunburn on a Sunny day.

RECTILINEAR PROPAGATION OF LIGHT
Light travel in a straight line. It is known as rectilinear propagation of light.

If you see the flame through the holes at same level, the flame is visible but if one of the cardboards is displaced such that the holes are not in straight line, the flame of the candle will not be visible. This suggests that light travels in a straight line.

PINHOLE CAMERA
A pinhole camera works on the principle of rectilinear propagation of light and pin-hole acts as a lens.

The box is closed from all sides and a forested glass sheet covers one side, containing a very small hole in the centre. An inverted image of the object is formed on it.

Do You Know : Artists from the sixteenth century onwards used a pinhole camera to help them get the correct colour proportions for a painting.SHADOWS AND IMAGES

Shadows
When light falls on an opaque object, it obstructs the path of light and shadow is formed. Thus shadow is the region of absence of light.

Do You Know : Shadow is comparatively long, in early morning and in late afternoon.

The main requirements for the formation of a shadow are :
(i) A source of light
(ii) An opaque obstacle
(iii) A screen behind the obstacle.

Important characteristics of a shadow
(1) Shadow is formed when path of light is obstructed through an opaque object.
(2) Shadow lies to the opposite side of the source of light.
(3) The size of a shadow changes according to the position of source of light w.r.t the object.

Image
When rays of light after reflection meet, then image of the object is formed. It is an impression of an object.

Do You Know : Image formed by convex mirror is always smaller than the object and the image formed by concave mirror may be larger, smaller or equal to the size of the object depending upon the position of the object from the mirror.

Comparison of shadow and image :

SOLAR AND LUNAR ECLIPSE
Solar and lunar eclipse are formed due to the shadows only.

Solar eclipse
We know that moon revolves around the earth. When moon comes in between the sun and the earth, then the shadow of moon falls on the earth creating darkness over a small region of earth. This incident is known as solar eclipse. Since the size of moon is smaller as compared to the sun, so the region of total darkness (umbra) is small and region of partial darkness (penumbra) is bigger

Lunar eclipse
During the revolution, earth comes between the sun and the moon then the shadow of the earth is formed on the moon, due to which it appears dark. This phenomenon is called as lunar eclipse. Since the size of the earth is bigger than that of the moon, so the region of total darkness (umbra) is more than the region of partial darkness (penumbra).

REFLECTION OF LIGHT
When a ray of light falls on an opaque object, it bounces back. This bouncing back of light into the same medium is called reflection of light. Non-luminous objects are visible because they reflect light rays falling on them.

Reflection of light from a smooth and rough surface 
Reflection of light from a smooth surface is called regular reflection. In regular reflection a parallel beam of incident light is reflected back as a parallel beam in one direction. Plane mirror and highly polished metal surfaces produce regular reflection. Images are formed by regular reflection.

Do You Know : In early age, mirrors were formed by polishing a volcanic rock called obsidian which was glassy and black.

When a parallel beam of light falls on a rough surface then light is reflected in different direction, it is known as diffuse reflection or irregular reflection. Rough surfaces like wall, table, cardboard, etc. produce diffuse reflection

Do You Know : We are able to see an object due to diffuse reflection.

LIGHT SHADOWS AND REFLECTIONS

ACTIVITY- 1 : To distinguish transparent, opaque and translucent objects.

More Question-

Q1. What are luminous and non-luminous objects? Give examples.

Q2. Differentiate between transparent, translucent and opaque objects withexamples.

Q3. What is a shadow? How is it formed?

Q4. List the conditions essential for the formation of a shadow.

Q5. Classify the following as transparent, translucent and opaque objects:

       a )Stone                                                   f) Wood

       b) Wax paper                                           g) Smoke

       c) Reading glasses                                   h) Leather

       d) Common salt                                       i) Blood

       e) Skin of a drum                                     j) Dense fog

Q6. What type of shadows are formed by transparent, translucent and opaue objects?

Q7. Why do we not see the shadow of aeroplanes and birds flying in the sky?

Q8. State the principle behind the working of a pinhole camera. Describe in detail how youwill make a simple pinhole camera at home.

Q9. List the characteristics of the image formed in a pinhole camera.

Q10. Describe an activity to show that light travels in a straight line.

Q11. Define reflection of light.

Q12. Fill in the blanks:

1. ____________ objects do not caste any shadow.

2. Moon is a _____________ object. (luminous/nonluminous)

3. Shadows give us information about the _____________ of the object.

4. Solar and Lunar eclipse are examples of _____________ formation in nature.

5. A _____________ changes the direction of light that falls on it.