Key Points

Objects that emit their own light, like the Sun and stars, are called luminous objects. Objects that reflect light from other sources, like the Moon, are called non-luminous objects.

Light travels in a straight line. This property is known as the rectilinear propagation of light and is the reason shadows are formed.

Transparent materials allow light to pass through almost completely, translucent materials allow partial passage, and opaque materials do not allow light to pass through at all.

A shadow is a dark area formed when an opaque object blocks the path of light. To observe a shadow, a source of light, an opaque object, and a screen are required.

A shadow is always dark, regardless of the object's color. Its size and shape depend on the distance and angle between the light source, the object, and the screen.

Reflection is the change in the direction of light by a mirror or another shiny surface. The light bounces off the surface, allowing us to see non-luminous objects.

An image formed by a plane mirror is erect (upright) and of the same size as the object. The image appears to be at the same distance behind the mirror as the object is in front of it.

The image formed by a plane mirror is a virtual image. This means it cannot be captured or projected onto a screen.

Images in a plane mirror are laterally inverted. This means the left side of the object appears as the right side of the image, and vice versa.

A pinhole camera is a simple device that works on the principle that light travels in a straight line. It uses a tiny hole to form an image on a screen.

The image formed by a pinhole camera is real (can be formed on a screen) and inverted (upside down). The image also displays the colors of the object.

A periscope uses two plane mirrors arranged parallel to each other to see objects that are not in the direct line of sight. It operates on the principle of reflection.

A kaleidoscope uses three plane mirrors joined together in a triangular shape to create multiple reflections, forming beautiful and changing symmetrical patterns.