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Reflection of Light (Laws of Reflection, Plane Mirrors) - SS1 Physics Lesson Note

The reflection of light occurs when light waves bounce off a surface and change direction. Reflection plays a significant role in our daily lives and is responsible for the formation of images in mirrors, the visibility of objects, and various optical phenomena. Let's explore the laws of reflection and the behaviour of light in plane mirrors:

1. Laws of Reflection:

The laws of reflection describe how light waves behave when they encounter a reflecting surface. These laws apply to all types of waves, including light waves. The laws of reflection are as follows:

-       The Incident Ray: The incident ray is the incoming ray of light that strikes the reflecting surface.

-       The Reflected Ray: The reflected ray is the ray of light that bounces off the reflecting surface after the incident ray strikes it.

-       The Normal: The normal is a line perpendicular to the surface at the point of incidence or the point where the incident ray strikes the surface.

-       Angle of Incidence: The angle of incidence is the angle between the incident ray and the normal.

-       Angle of Reflection: The angle of reflection is the angle between the reflected ray and the normal.

The laws of reflection state that:

-       The incident ray, the reflected ray, and the normal all lie in the same plane.

-       The angle of incidence is equal to the angle of reflection.

2. Reflection in Plane Mirrors:

Plane mirrors are flat mirrors with smooth and reflective surfaces. When light waves strike a plane mirror, they undergo reflection according to the laws of reflection. The key points regarding reflection in plane mirrors are:

-       Virtual Images: Plane mirrors produce virtual images, which are images formed by the apparent intersection of reflected light rays. These images cannot be projected onto a screen and are located behind the mirror.

-       Image Characteristics: The image formed in a plane mirror is upright, of the same size as the object, and located at the same distance behind the mirror as the object is in front of it.

-       Lateral Inversion: Plane mirrors produce laterally inverted images, meaning that the left side of the object appears as the right side in the image and vice versa. This effect is due to the reversal of the directions of the light rays during reflection.

Reflection in plane mirrors is widely used in everyday applications, such as mirrors in bathrooms, dressing rooms, and rear-view mirrors in vehicles. It also forms the basis for various optical devices, including periscopes, kaleidoscopes, and some telescopes.

Understanding the laws of reflection and the behaviour of light in plane mirrors is crucial for comprehending the formation of images, studying optics, and designing optical systems.

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