Topics
- 1. Light
- 2. Transparent Opaque and Translucent Objects
- 3. Shadows
- 4. Pinhole Camera
- 5. Light travels in a straight line
- 6. Mirror and Reflection
Light
Light is a form of energy which is responsible for the sense of sight.It enables to see things around us.
- Light enables us to see every object around us like trees, vehicles, houses, people, etc.
- At night due to the absence of sunlight, it becomes dark, which reduces our visibility.
- Objects that emit light are calledย Luminous Objectslike sun, bulb, tubelight.
- Any non-light emitting object is visible when light from a luminous source falls on that object and then reaches our eye.These objects are calledย Non-Luminous Objectsย like trees, animals, shoe, moon (it seems glowing because of sunโs light falling on it) etc.
Transparent, Opaque and Translucent Objects
Objects are classified based on amount of light that can pass through them.
| Opaque | Translucent | Transparent |
| These objects do not allow light to pass through them. | These objects allow light to pass through them partially. | These objects allow light to pass through them completely. |
| We canโt see through these objects. | We can see through these objects a little but not clearly. | We can see through these objects clearly. |
| Examples wall, door, trees etc. | Examples polythene, butter paper, thin plastic sheet etc. | Examples air, water, clear glass, etc. |
 |  |  |
Shadows
A shadow is a space where light from a light source is blocked by an opaque object.
- A shadow is formed when a part of light is blocked by the object. If all the light is blocked by an object, then there will not be any shadow.
- Shape of the shadow is always similar to that of the object but the size varies.
- Shadows of different types of objects may have similar shape as the amount of light they may be blocking is same.
- Shadows cannot occur in dark rooms (due to absence of light) and full lit rooms with no objects (due to absence of opaque object).
- A shadow is always obtained on a screen like walls, ground etc.
A shadow is always black or grey irrespective of the colour of the object
Pinhole Camera
A pinhole camera is a simple camera, without lens, in the shape of a box. One of the sides has a small hole and it produces an inverted image of the outside world at other side.
- The box should be painted black from outside and inside for better clarity.
- The object whose image is to be seen should be in bright light.
- Smaller the hole, sharper the image.
- Temporary Black and White images are formed on the screen if a tracing paper is used. Permanent colored and b & w images can be obtained using photographic films instead of tracing paper.
- In the below diagram, two boxes are placed one inside the other. The image of the outer object is created inverted on the inner box translucent screen.
Light travels in a straight line
- Light always travel in straight lines.
Blocking of such straight moving light rays by opaque objects results in shadows. Shadows canโt be formed if the light rays do not travel in straight lines
Mirror and Reflection
Light waves may change their direction upon striking a surface. This is called reflection. Mirror is an object which reflects light.
- Shiny and polished surfaces usually act as mirrors.
- Due to reflection, image of an object is seen in the mirror.
- Mirror changes the direction of light falling on it.
