Class -6, Science, Chapter:- 11 (Light, Shadows & Reflections), Notes, NCERT Solutions & Frequently Asked Questions

Science

Class:-6, Chapter:- 11

(Light, Shadows & Reflections)

Notes, NCERT Solutions & Frequently Asked Questions

-- Notes --

⭐Light as a form of energy:- 

• Light is the energy that enables us to see.

• Light is emitted from a source such as the Sun.

⭐Source of light:- An object which emits light, is called a source of light. For example, sun, torch, etc.

⭐Ray of light:- A straight thin beam of light from a source to an object is called a ray of light.

⭐Obstacle:- An object which comes to the path of the light is called an obstacle.

⭐Rectilinear propagation of light:- Light takes the quickest path between any two points. Therefore, light travels in a straight line. This is known as a rectilinear propagation of light.

⭐Luminous & Non-luminous objects:-

• Objects that emit light and heat are known as luminous objects. Eg.- Sun and other stars

• Objects that do not produce their own light but reflect the light emitted by luminous objects are known as non-luminous objects. Eg.- Earth, trees

⭐Transparent, opaque and translucent objects:- Objects can be classified based on their interaction with light as follows:-

• Transparent objects allow light to pass through them without getting scattered. Eg.- glass

• Translucent objects allow light to pass through them partially. Eg.- Butter paper

• Opaque objects do not allow any light to pass through them. Eg.- a table, a book, etc

⭐Shadow:- Opaque objects do not allow light to pass through them and cast dark patches behind them. These dark patches are called shadows.

⭐Shadow formation:- A shadow is formed when an opaque object comes in the path of light.

•A shadow needs a screen where it is formed, for example, the ground, or walls of a room or even the surfaces of buildings.

• Shadows give us an idea about the shapes of different objects. Or, it can even mislead us about the shape of different objects. Eg.- the shadow of a cone appears to be a triangle on the screen.

⭐Characteristics of a Shadow:- A shadow has the following three characteristics:-

• It is always black, regardless of the colour of the object used to make the shadow. 

• It only shows the shape or outline of the object and not the details.

• The size of a shadow varies depending on the distance between the object and the source of light, and the distance between the object and the screen.

⭐The Pinhole Camera:- 

(Formation of image by pinhole camera)

• A pinhole camera is a simple camera that consists of a light-proof box, a thin film for a screen and a small aperture or hole to allow the passage of light rays.

• The light from outside enters through the small hole and forms an image on the screen that is inverted.

⭐Mirrors:- A mirror is a surface usually consisting of a glass that reflects light incident on it to form clear erect images.

⭐Reflection:- When light is incident on a surface, it gets reflected or it bounces back. Any surface that is really well polished or shiny acts like a mirror. The phenomenon of light bouncing off surfaces is called reflection.

⭐Characteristics of images:-

• Images have colour, unlike shadows. • They are formed due to the converging rays of light that comes after reflecting from objects.

• A real image is formed by actual convergence of light rays. Real images always form on a screen.

• A virtual image is the apparent convergence of diverging light rays. Virtual images cannot be obtained on a screen.

⭐Plane mirrors and images formed by them:- A plane mirror changes the direction of light that falls on it.

• This enables us to see images. Take the example of a comb placed in front of a mirror over a dark coloured paper. Let a beam of light pass through the comb on the mirror using a torch. Then an image is observed similar to the one given :

• We observe that the light gets reflected from this mirror and it travels in straight lines.

⭐Lateral inversion:- Right side of the object appears as left side in the image formed by a plane mirror. Eg.- if we show our right hand, image in the mirror will show as left hand.

⭐ Difference between Shadow & Image:- 

-- NCERT Solutions --

Exercise Questions

Question 1.- Rearrange the boxes given below to make a sentence that helps us understand opaque objects.

Opaque objects puzzle

Solution:- The given boxes can be rearranged to form ‘Opaque Objects Make Shadows’ as shown below:-

Opaque objects puzzle

Question 2.- Classify the objects or materials given below as opaque, transparent or translucent and luminous or non-luminous:-

Air, water, a piece of rock, a sheet of aluminum, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, a piece of red hot iron, an umbrella, a lighted fluorescent tube, a wall, a sheet of carbon paper, the flame of a gas burner, a sheet of cardboard, a lighted torch, a sheet of cellophane, a wire mesh, kerosene stove, sun, firefly, the moon.

Solution:-

Opaque:- A piece of rock, a sheet of aluminium, a mirror, a wooden board, a CD, an umbrella, a wall, a sheet of carbon paper, a sheet of cardboard.

Transparent:- Air, water, a sheet of plane glass.

Translucent:- A sheet of polythene, smoke, fog, a sheet of cellophane, a wire mesh.

Luminous:- A piece of red hot iron, a lighted fluorescent tube, the flame of a gas burner, a lighted torch, sun, firefly, kerosene stove.

Non – luminous:- Air, water, a piece of rock, a sheet of aluminium, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, an umbrella, a wall, a sheet of carbon paper, a sheet of cardboard, a sheet of cellophane, a wire mesh, moon.

Question 3.- Can you think of creating a shape that would give a circular shadow if held in one way and a rectangular shadow if held in another way?

Solution:- Yes, there are many things which give a circular shadow if held in one way and a rectangular shadow if held in another way. For example: a cylinder, a circular disc etc.

Question 4.- In a completely dark room, if you hold up a mirror in front of you, will you see a reflection of yourself in the mirror?

Solution:- No, in a dark room, a mirror reflection of the image will not be shown as the light will not fall on the mirror to reflect the image due to darkness. 

-- Frequently Asked Questions --

Question 1.- Whether the moon is luminous or non-luminous body?

Answer:- Moon is non-luminous body.

Question 2.- What is umbra?

Answer:- Umbra is the dark region behind object facing light which does not receive light at all.

Question 3.- How does a light ray travel?

Answer:- Light ray travels in a straight line.

Question 4.- Give one natural source of light. 

Answer:- Sun is a natural source of light.

Question 5.- What is shadow? 

Answer:- Shadow is the dark space behind an opaque object where light does not reach.

Question 6.- What is penumbra?

Answer:- The less darker shadow formed shadow on the periphery of dark shadow is called penumbra.

Question 7.- State difference between a luminous and a non-luminous body.

Answer:- 

• The bodies which emit light are called luminous bodies. Example: sun, stars, burning candle etc.

• The bodies which does not emit light are called non-luminous bodies. Example: moon, earth, blackboard.

Question 8.- Why is the moon not considered as a luminous body?

Answer:- Moon is non-luminous body because it shines by reflecting the sunlight falling on it.

Question 9.- What is an incandescent body? Give example.

Answer:- The bodies which emit light when heated to a very high temperature are called incandescent bodies. Example: electric bulb.

Questions 10.-  When does a shadow form?

Answer:-  Shadow is formed when light does not reach behind the opaque object kept in the path of light

Question 11.- What are the essential conditions for the formation of shadow?

Answer:- 

(1) There should be an opaque material.

(2) There should be a source of light and screen.

(3) The object must be placed in the path of light. Then shadow is formed on the screen.

Question 12.- Define reflection of light.

Answer:- When light rays after striking the smooth and shiny surface return to same medium, this phenomenon is called reflection of light.

- By Durgesh Pandey