Chapter Notes and Summary
• Light is a form of energy which helps us to see objects.
• Light is also an electromagnetic radiation that we can detect.
• Light does not need any material medium. It can even travel through vacuum.
• Light is essential for existence of life.
• natural warmth of sunlight creates conditions conductive for growth and development of life.
• Light is main source of energy for animal and plants.
• Light travels in a straight line.
• Those objects that emit light of their own are called luminous objects. e.g., bulb, torch, sun etc.
• Those objects that do not emit light of their own are called non-luminous object. e.g.,. chair, paint etc.
• Those objects that allow light to pass through them completely are called transparent objects. e.g., polythene, water, glass, air etc.
• Those objects that do not allow light to pass through them are called opaque objects. e.g., wood, mud, sand, bricks etc.
• Those objects that allow light to pass through them only partially are called translucent materials. e.g., tracing paper, mica, wax, sheet of white cotton etc.
• dark patches formed behind an opaque objects, when comes in way of light are called shadows.
• A screen or surface is required for shadow to form.
• Irrespective of colour of object, shadow is always black.
• A shadow shows only outline or shape of object.
• A small object will have a small shadow while a large object will have a large shadow.
• When distance between object and source of light is decreased, shadow becomes larger.
• When distance between object and source of light is increased, shadow becomes smaller.
• When distance between object and screen is decreased, shadow becomes smaller.
• When distance between object and screen in increased, shadow becomes larger.
• dark part of shadow is called umbra.
• partially dark part of shadow is called penumbra.
• path along which light travels in a particular direction is known as ray of light.
• A beam of light is large number of rays of light that travel in a given direction.
• A pinhole camera is a device to show that light travels in a straight line.
• Image formed by a pinhole camera is inverted and real as it can be received on screen.
• A plane mirror is a smooth plane surface that reflects entire light incident on it.
• Light incident on an object is reflected to our eyes.
• Due to reflection, we can see images. image is a reflection of an object.
• When a light ray is incident on an object, it is called incident ray and ray which reflects back is called reflected ray.