photo.jpg

## Lesson 16: Light and Associated Phenomena ### Warm Up! Light enables us to see the world. Light is a form of energy. It illuminates objects it falls on. You had learnt about light in Class VI. Can you fill in the blanks recalling what you learnt previously? ### Rectilinear Propagation of Light...

## Lesson 16: Light and Associated Phenomena ### Warm Up! Light enables us to see the world. Light is a form of energy. It illuminates objects it falls on. You had learnt about light in Class VI. Can you fill in the blanks recalling what you learnt previously? ### Rectilinear Propagation of Light Rectilinear propagation of light refers to the tendency of light to travel in straight lines in a uniform, transparent medium. (Rectilinear means "moving in or created from straight lines"). Examples include beams of light in flashlights, searchlights, stage spotlights, and car headlights that appear to travel in straight lines. * Light travels in a straight line as it remains in the same (uniform) medium. * A light beam is light travelling in one direction. * Light rays travel in a straight line nearly 30,000 kilometres per second. * When the path of light is blocked by an opaque object, it prevents the beams from passing through, producing shadows. * Light also can change direction when it moves from one medium to another. ### Activity 1: To Show Light Travels in Straight Lines **Materials required:** * A cardboard of about 10 inches * A straw **Method:** * Hold the cardboard with one end to the straw and the other held to your eyes. * See the light passing through the straw. Now, bend the straw a little bit. * Can you see the light passing through the hole? **Observation:** * You can clearly see the light passing through the straw because light travels in a straight line. * When the path of light is blocked by the straw, the light is no longer visible because the straw doesn't allow the light to pass through it. This clearly shows that light travels in a straight line. * The straw is bent to the extent that it blocks the light and the light is no longer visible. This shows that light travels in a straight line. ### Activity 2: To Create a Shadow **Aim:** * To create shadows from a light source with circular and rectangular objects. **Materials required:** * A flashlight * A circular object * A rectangular object