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
Luminous objects: An object which has a tendency to produce light are known as luminous objects. Example: Sun, bulb, etc.
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
(images will be uploaded soon)
Types of Object
Transparent Object: An Object through which light is completely passed known as transparent object. We can clearly see through a transparent object.
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.
Opaque Object: An object which does not allow passage to light is called an opaque object. We cannot see through an opaque object.
What is the Shadow?
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
Shadow is always in erected form.
It is always in real form.
Color of the shadow is always black.
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
Image is the same size and color as the object.
Real image is formed.
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
It is used to view objects like trees and buildings.
It is also used to take photographs.
Principle
It works on the principle that light travels in a straight line.
(image will be uploaded soon)
FAQs on Light Shadow and Reflection
1. What is meant by the propagation of light, and how does it affect the formation of shadows?
Propagation of light refers to the way light travels in a straight line through a medium. This property is why shadows form when an object blocks light from a source. The shadow's size and sharpness depend on the distance between the light source, the object, and the screen.
2. What key differences exist between transparent, translucent, and opaque objects?
- Transparent objects: Allow almost all light to pass through (e.g., glass); objects on the other side are clearly visible.
- Translucent objects: Allow partial passage of light, causing blurred visibility (e.g., butter paper).
- Opaque objects: Do not allow light to pass through; objects behind cannot be seen (e.g., wood).
3. Why is the color of a shadow always black, even if the object or light source is colored?
A shadow appears black because it is a region where light is blocked by an opaque object. Since no or very little light reaches this area, it lacks color information from the light source or object, resulting in a dark or black appearance, regardless of object or source color.
4. How does the distance between the object, the light source, and the screen affect the size of the shadow?
- If the object is closer to the light source, its shadow on the screen appears larger.
- If the object is farther from the light source or closer to the screen, the shadow becomes smaller and sharper.
- The angle at which light falls also influences the shadow's length and orientation.
5. What principle does a pinhole camera demonstrate and how does it work?
A pinhole camera works on the principle that light travels in straight lines. It consists of a closed box with a small hole on one side and a translucent screen opposite it. When light from an object passes through the hole, it forms a real, inverted image on the screen.
6. How do the images formed by reflection differ from shadows?
- Reflected images are produced by light bouncing off a smooth surface, like a mirror. These images can show color and detail, and are usually the same size as the object.
- Shadows are formed when an object blocks light, creating a dark outline. Shadows do not show color or detail and are always black.
7. What are the laws of reflection, and what features does a mirror image have?
- The laws of reflection state: (1) The angle of incidence equals the angle of reflection. (2) The incident ray, reflected ray, and normal all lie in the same plane.
- A mirror image is upright, of the same size and color as the object, but laterally inverted (left and right are reversed).
8. Can shadows be larger, smaller, or equal to the size of the object? Under what conditions?
Shadows can appear larger, smaller, or the same size as the object depending on the position of the object relative to the light source and the screen. Closer to the light source means a larger shadow; farther away or closer to the screen means a smaller shadow.
9. What are luminous and non-luminous objects? Can you give examples from everyday life?
- Luminous objects produce their own light (e.g., Sun, bulb).
- Non-luminous objects do not produce light; they are visible only when they reflect light from a luminous source (e.g., Moon, table).
10. How does the angle of incidence affect the shadow length during different times of the day?
When the Sun is low in the sky (morning/evening), the angle of incidence is small, creating longer shadows. At noon, when the Sun is overhead, the angle is larger and shadows are the shortest.
11. What would happen if pinhole cameras were made with larger holes? How would the image quality change?
If a pinhole camera has a larger hole, the image will become blurred due to the entry of multiple light rays from each point of the object, causing overlapping. A smaller pinhole produces a sharper image by allowing only straight-line rays from each point.
12. Why can’t we see objects in total darkness, even if they are close to us?
We cannot see objects in complete darkness because there is no light to reflect off the objects and reach our eyes. Sight depends on the presence of light to make objects visible.
