View Notes

## Light

It is a form of energy which makes objects visible as we cannot see objects in darkness.During day time sunlight acts as a source of energy which makes everything visible whereas at night we use artificial sources of light for seeing objects. As when light falls on an object, light gets reflected and this reflected light comes to us which makes the object visible. An object which is known as a source of light. Some common examples of sources of light are sun, bulb,etc. Sun is the universal source of light. It is approx 1500 km away from us then also it brightens all universe.

### Natural and Man Made Source of Light

Natural Source of Light: Source of light which is already present in nature known as natural source of light. Example: Sun.

Man Made Source of Light: Source of light which is prepared by humans is known as man made source of light. Example: bulb, candle, torch, etc.

### Classification of Object Based on Tendency to Produce Light

1. Luminous objects: An object which has a tendency to produce light are known as luminous objects. Example: Sun, bulb, etc.

2. Non - luminous object: An object which does not have a tendency to produce light known as a non-luminous object. Example: moon.

### Propagation of Light

From the experiment below we will prove that light travels in a straight line i.e path covered by light is alway straight.

• For this, take a cylindrical tube; which can be easily bent.

• Try to see a source of light; like a bulb or a candle; through the straight tube.

• Once the tube is bent at some angle, it is not possible to see the source of light through it.

• This happens because light travels in a straight line.

Figure Showing Propagation of Light

Types of Object

1. Transparent Object: An Object through which light is completely passed known as transparent object. We can clearly see through a transparent object.

2. Translucent Object: An object which allows partial passage to light is called a translucent object. We can see through a translucent object but the vision would be murky.

3. Opaque Object: An object which does not allow passage to light is called an opaque object. We cannot see through an opaque object.

When a ray of light falls on an opaque object, a dark patch is formed on the other side of the object whether it is on ground or it is on screen present on the other side of the object. Three things are required for the formation of shadow, viz a source of light, an object and a screen. The size of shadow totally depends on distance between object and source of light. Closer the source of light, larger will be the size of the shadow. Far the source of light is, smaller is the shadow.

In case if the incidence angle is smaller, shadow is longer. On the same side if the incidence angle is bigger, the shadow is smaller. This concept is well proved with a smaller size of shadow in the evening and noon and bigger size of shadow in the morning.

### Features of Shadow of an Object

1. Shadow is always in erected form.

2. It is always in real form.

3. Color of the shadow is always black.

4. It can be smaller than object, bigger than object or same size to object.

### Light and its Reflection

Reflection occurs mainly on the mirror surface as incident light gets reflected when it falls on a clear surface and due to reflection the image formed is always erect.

Reflection

When a ray of light falls on a surface like glass which has shiny and glossy properties from where light gets reflected. This phenomenon of bouncing back of light is known as reflection.

During reflection angle of incidence is equal to angle of reflection.

Features of Image Formed Due to Reflection

1. Image is the same size and color as the object.

2. Real image is formed.

3. Right side of the object appears to be left in image and vice-versa.

### Formation of Image in Pinhole Camera

Pinhole cameras consist of a closed box having a small pinhole in the front and having translucent screen at the back. Pinhole camera is made up of translucent butter paper. This is the reason we can see objects in a pinhole camera.

Uses of Pinhole Camera

1. It is used to view objects like trees and buildings.

2. It is also used to take photographs.

Principle

It works on the principle that light travels in a straight line.

1. Define Light?

Ans. It is a form of energy which makes objects visible as we cannot see objects in darkness.

During day time sunlight acts as a source of energy which makes everything visible whereas at night we use artificial sources of light for seeing objects. As when light falls on an object, light gets reflected and this reflected light comes to us which makes the object visible.

2. Explain the Law of Reflection?

Ans. Reflection occurs mainly on the mirror surface as incident light gets reflected when it falls on a clear surface and due to reflection the image formed is always erect.

Reflection:

When a ray of light falls on a surface like glass which has shiny and glossy properties from where light gets reflected. This phenomenon of bouncing back of light is known as reflection.

During reflection angle of incidence is equal to angle of reflection.

Features of Image Formed Due to Reflection:

1. Image is the same size and color as the object.

2. Real image is formed.

3. Right side of the object appears to be left in image and vice-versa.

3. What is a Pinhole Camera?

Ans. Pinhole cameras consist of a closed box having a small pinhole in the front and having translucent screen at the back. Pinhole camera is made up of translucent butter paper. This is the reason we can see objects in a pinhole camera.

4. Classify Objects Based on its Light Producing Property?

Ans. Mainly there are two types of object based on their light emitting property:

1. Luminous Objects: An object which has a tendency to produce light are known as luminous objects. Example: Sun, bulb, etc.

2. Non - Luminous Object: An object which does not have a tendency to produce light known as a non-luminous object. Example: moon.