i. Light: Laws of Reflection, Types, and Optical Law

delete UPSC Sample Notes [English]

i. Light: Laws of Reflection, Types, and Optical Law

Laws of Reflection: Illuminating the Science of Reflected Light

An object reflects light that falls on it. This reflected light is received by our eyes and enables us to see things. We are able to see through a transparent medium as light is transmitted through it. Objects like the sun that give out or emit light of their own are called luminous objects. There are a number of phenomena associated with light such as image formation by mirrors, the twinkling of stars, the beautiful colours of a rainbow, bending of light by a medium and so on, all of which are intricately connected with the principles encapsulated in the laws of reflection.

Laws of Reflection: Illuminating the Path of Light

Laws of Reflection and Optical Wonders: After striking the mirror, the ray of light is reflected in another direction.
The light ray, which strikes any surface, is called the incident ray.
The ray that comes back from the surface after reflection is known as the reflected ray.
First Law of Reflection: Equal Angles of Incidence and Reflection: The angle of incidence (i) is equal to the angle of reflection (r).
This can be stated as: i=r.
- When a ray of light strikes a surface and is reflected, the incident ray, the reflected ray, and the normal (a line perpendicular to the surface at the point of incidence) all lie in the same plane.
  - The angle between the incident ray and the normal is the angle of incidence, and the angle between the reflected ray and the normal is the angle of reflection.
  - According to the first law of reflection, these two angles are equal.

Second Law of Reflection: Plane of Reflection: The incident ray, the reflected ray, and the normal all lie in the same plane.
- This law emphasises that reflection occurs in a specific plane.
- The incident ray and the reflected ray, along with the normal, all exist on the same plane defined by the surface of reflection.

What distinguishes Diffused and Regular Reflection and how are they Governed by the Laws of Reflection in the world of Light?

Diffused or irregular reflection: Impact of Surface Roughness: When all the parallel rays reflected from a rough or irregular surface are not parallel, the reflection is known as diffused or irregular reflection.
Diffused reflection is not due to the failure of the laws of reflection. It is caused by the irregularities in the reflecting surface.
Regular reflection: Formation of Images: On the other hand, reflection from a smooth surface like that of a mirror is called regular reflection. Images are formed by regular reflection.

Do We See all Objects due to Reflected Light?

Nearly everything we see around is seen due to reflected light. The Moon, for example, receives light from the Sun and reflects it. The objects which shine in the light of other objects are called illuminated objects. There are other objects, which give their own light, such as the Sun, fire, flame of a candle and an electric lamp. Their light falls on our eyes. That is how we see them. The objects which emit their own light are known as luminous objects.

Image Characteristics: Mirrors, Lenses, and the Optical Marvels

In a plane mirror the image is formed behind the mirror. It is erect, of the same size and is at the same distance from the mirror as the object is in front of it. An image formed on a screen is called a real image. The image formed by a plane mirror that could not be obtained on a screen is called a virtual image.
In an image formed by a mirror, the left side of the object is seen on the right side in the image, and the right side of the object appears to be on the left side in the image.
A concave mirror can form a real and inverted image. When the object is placed very close to the mirror, the image formed is virtual, erect and magnified. Image formed by a convex mirror is erect, virtual and smaller in size than the object.
A convex lens can form a real and inverted image. When the object is placed very close to the lens, the image formed is virtual, erect and magnified. When used to see objects magnified, the convex lens is called a magnifying glass.
A concave lens always forms an erect, virtual and smaller image than the object.