CBSE Class 6 Science Light Shadows And Reflections Notes

CBSE Class 6 Science - Light, Shadows and Reflections Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations. 

Topics in the chapter

- Light
- Luminous objects
- Non-Luminous objects
- Transparent, Opaque and Translucent Objects
- Characteristics of light
- Shadow and its properties
- Pinhole camera
- Mirror and types of mirror

Light

- It is a form of energy which is responsible for seeing objects.
- When light falls on an object, some light get reflected, this reflected light come to our eyes and we are able to see an object.
- Example: sun, torch, candle, fireflies and glow worm etc.

Sources of light

(i) Luminous object: The objects which emit their own light is called luminous object.
- Example: sun, torch bulb, star
(ii) Non-luminous object: The objects which do not emit their own light is called non-luminous object.
- Example: Moon, shoe, trees.

Types of materials transmit light

- There are three types of materials which transmit light:
(i) Transparent
(ii) Translucent
(iii) Opaque

(i) Transparent
- These objects allow light to pass through them in straight line completely.
- We can see through these objects clearly.
- Examples: air, water, etc.

(ii) Translucent
- These objects allow light to pass through them partially.
- The object is not clearly seen in translucent object.
- Examples: Tissue paper, frosted glass, butter paper, etc.

(iii) Opaque
- These objects do not allow light to pass through them.
- We can’t see the object through this.
- Examples: wall, door, trees etc.

Characteristics of light

- Light travels in straight line
- Light can be reflected
- Light can be bent
- The speed of light is 3 × 108 m/sec
- Light can be polarized

Shadow

- When an opaque object blocked the path of light it forms a dark portion on the opposite side of the object this dark portion is known as shadow.

Properties of shadow
- The object must be opaque or translucent
- Transparent object do not make shadow
- It is dark in color
- It is formed opposite to the source of light
- It gives the information about the shape of object
- Size of shadow can be increase or decrees by change in distance between object and screen are changed.

Pin hole camera

- It is a toy device use to study light travels in straight line Properties of image formed by a Pin Hole Camera
(i) Image formed by a pin hole camera is coloured.
(ii) Image formed by a pin hole camera is inverted.
(iii) Image formed by a pin hole camera is smaller in size.

Rectilinear propagation of light

- Light travels in a straight line are called rectilinear propagation of light.
Important terms regard rectilinear propagation of light
(i) Ray of light: It is a path along which light travels in the given direction.
(ii) Beam of light: Bunch of ray of light travel in the given direction.

Mirror

- A mirror is a polished surface which can make the image of an object.

Types of Mirror
(i) Plane mirror: Image formed is of the same size
(ii) Concave mirror: Reflecting surface is bent–in.
(iii) Convex Mirror: Reflecting surface is bulged-out.

Reflection
- When light falls on a mirror, light wave may change their direction upon the striking surface this phenomena is called reflection.

Ql.  Does the flame of a gas stove emit light?

Ans. Yes. 

Q2.  What is rectilinear propagation of light? 

Ans. Light travels in a straight line. 

Q3.  Write the names of 4 different sources of light? 

Ans. Bulb, sun, stars, firefly 

Q4.  Give one example of living thing which emits light? 

Ans. Jugnu (firefly) 

Q5.  Sometimes you are able to see sun or moon behind the clouds .What can you say ability of such clouds to transmit light? 

Ans. Yes, clouds transmit light. 

Q6.   Image formed in a pinhole camera is inverted .Why? 

Ans. It is inverted because of the rectilinear propagation of light. 

Q7.  Can you suggest the shape of the shadows? 

Ans. It is usually similar to the object.          

Q8. Does the length of shadow change from season to season?  

Ans.Yes if observed at same time . 

Q9. What is shadow?

Ans. A dark patch formed behind an opaque object when it is placed in the path of light.

Q10. What do you mean by reflection of light?

Ans. Coming back of light ray incident on a surface is called reflection.

Q11. What is the principle of working f a pin hole camera?

Ans. A pinhole camera is based on rectilinearpropagation of light?

Q12. Can light pass through opaque objects?

Ans. No

Q13. What is an artificial source of light?

Ans. Man made sources of light. For example: electric bulb, candle etc.

Q14. Classify the following into transparent, translucent, and opaque objects. (Glass, air, oil paper, rubber sheet)

Ans. Transparent: air, glass Translucent: oil paper Opaque: rubber sheet

Q15. Name two artificial sources of light?

Ans. Electric bulb, candle

Q16. Name one transparent and one opaque body?

Ans. Transparent: air

        Opaque: stone

 QUESTIONS

Ql. Define reflection of light?

Ans. The process of returning (Or bouncing back) the light to the same medium after Striking a surface is called reflection of light.

Q2. What is a reflector?

Ans. A surface which reflects the light is called reflector.

Q3. Give one example of most commonly used reflector?

Ans. Looking glass or plane mirror

Q4. Does the reflection of light from the surface similar to the bouncing back of a rubber ball after it strikes from a ball? Explain.

Ans. Yes, because of reflection, light falling on a surface bounces back to the same medium.

Q5. Give the difference between virtual image and real image?

Ans. 

        Real image                                                         Virtual image

It can be obtained on a screen                           It can't be obtained on a screen.

It is always inverted.                                          It is always upright (i.e. erect)

Real image is formed in                                    Virtual image is formed behind

front of the mirror.                                             the mirror.

Q6. Give the properties of the image formed by the pane mirror?

Ans. l. The image formed by plane mirror is erect and virtual.

2. Size of the image formed by plane mirror is equal to the size of the object.

3. The distance of the image behind the plane mirror is equal to the distance of the object from the mirro

Q7. Define luminous objects?

Ans. The objects which emit light are called luminous objects.

Q8. What is light?

Ans. Light is a form of energy which produces the sensation of sight.

Q9. What are non luminous objects?

Ans. Objects which do not emit their own light.

QlO. Why do objects in a room become visible even if sunlight does not enter it?

Ans. The objects in a room become visible, even if the sunlight does not enter the room because the air around the objects allows the scattered light to pass through it and we can see the objects.

Qll. How can you convert a transparent glass sheet into a translucent glass sheet?

Ans. By covering one side with butter paper.

Ql2. Does the colour of the shadow depend upon the colour of the object?

Ans. No, it is always dark.

Ql3. n a completely dark room, if you hold up a mirror in front of you, will you see a reflection of yourself in the mirror?

Ans. No, because there is no source of light .We can see our image only when light is reflected from the mirror.

Ql4. Give few examples of opaque, translucent and transparent objects?

Ans. Opaque: a piece of rock, a sheet of aluminium, a mirror, a wooden board, a wall a sheet, a sheet of cardboard, a CD

Translucent: a sheet of polythene , smoke, fog, a sheet of carbon, a sheet of cellophane.

Transparent: air, water, a sheet of plane glass

Q15. What do you understand by lateral inversion?

Ans. The right side of the object appears to be the left side of its image and vice-versa This is called lateral inversion.

Ql6. Give one example to show that light travels in a straight line?

Ans. When sunlight falls on a solid object like a building or a stone, a shadow is formed behind the solid object (opaque object) .This shows that light travels in a straight line.

Ql7. Distinguish between transparent, translucent and opaque materials?

Ans. Transparent materials: which allow light to pass through them and through which we can see clearly are known as transparent materials.

Translucent materials: substances through which light can pass partially and through which we can't see clearly are called translucent materials.

Opaque materials: substances which don't allow light to pass through them at all are called opaque materials.

Ql8. Can the opaque object cast shadow?

Ans. In the presence of light, opaque objects act as obstacles to propagate (travel) light and form a shadow behind them

QUESTIONS

Ql. How are shadows formed?

Ans. Light coming from the source of light falling on the objects gets obstructed by the objects and does not go ahead. So, a shadow is formed.

Q2. How can we protect our eyes while glaring at a strong source of light?

Ans. By placing our hand in front of our eyes, light coming from the source does not fall on our eyes directly. (Since we know light travels in a straight line.)

Q3. What happens when light falls on an object?

Ans. l. It is almost completely transmitted through the object.
2. Only one part of it may be transmitted and the rest is absorbed or spread out.
3. It may not be allowed to pass through at all.

Q4. Consider a wooden stick about half a meter long. Fix one end of it in open ground where there are no trees and buildings near it. Look its shadow in the morning and mark its points of shadow. Note the direction of sun with respect to stick. Where is shadow of the object formed?

Ans. The shadow of the object is formed in the direction opposite to the side of the source light i.e. it is formed opposite to the direction of the sun. This activity also shows that shadow moves according to the movement of the sources of light and the length of the shadow changes with time and the shadow of an object is formed in the direction opposite to that of the source of light.

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