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Reflection 

The process through which light rays fall on the surface and gets bounced back is known as a reflection of light.

Reflection from plane mirrors

Regular Reflection:

The plane mirrors with a smooth surface produce this type of reflection. In this case, the image is clear and is very much visible. The images produced by plane mirrors are always virtual, that is they cannot be collected on a screen.

Regular reflection occurs when a parallel beam of light falls on a plane mirror band reflected as a parallel beam. They occur on polished surfaces.

In the case of curved mirrors with a smooth surface, we can see the images of reflection either virtually or really. That is, the images produced by curved mirrors can be either real (collected on a screen and seen), or virtual (cannot be collected on a screen, but only seen).

Irregular Reflection ( diffused Reflection):

Unlike mirrors, most natural surfaces are rough on the scale of the wavelength of light, and, as a consequence, parallel incident light rays are reflected in many different directions irregularly, or diffusely.

 A diffuse reflection occurs on rough surfaces where a parallel beam of light is reflected in all directions.

Hence, diffuse reflection helps in seeing the objects and is responsible for the ability to see most illuminated surfaces from any position.

In both regular and irregular reflections, the laws of reflection are followed.

 Law of reflection

1. The incident ray, the normal and the reflected ray at the point of incidence must be on the same plane
2. The angle of incidence is equal to the angle of reflection.

The law states that when the light rays falls on the smooth surface, the angle of reflection is equal to the angle of incidence, also the incident ray, the reflected ray, and the normal to the surface all lie in the same plane.

The law of reflection formula is given as:

θi = θr

Where,

θi is the angle of incidence

θr is the angle of reflection

The angle of reflection Θr of a ray is the angle measured from the reflected ray to the normal surface.

Characteristics of images formed in a plane mirror

1. The image is the same size as the object
2. The image is the same distance behind the mirror as the object is in front
3. The image is laterally inverted
4. The image is virtual
5. The image is erect.

Concave Mirror

If a hollow sphere is cut into parts and the outer surface of the cut part is painted, then it becomes a mirror with its inner surface as the reflecting surface. This kind of mirror is known as a concave mirror.

Light converges at a point when it strikes and reflects back from the reflecting surface of the concave mirror. Hence, it is also known as a converging mirror.

When the concave mirror is placed very close to the object, a magnified and virtual image is obtained. However, if we increase the distance between the object and the mirror then the size of the image reduces and a real image is formed.

 So, the image formed by the concave mirror can be small or large and it can also be real or virtual.

Convex Mirror

If the other cut part of the hollow sphere is painted from inside, then its outer surface becomes the reflecting surface. This kind of mirror is known as a convex mirror.

A convex mirror is also known as a diverging mirror as this mirror diverges light when they strike on its reflecting surface. Virtual, erect, and diminished images are always formed with convex mirrors, irrespective of the distance between the object and the mirror.

Apart from other applications, the convex mirror is mostly used as a rear-view mirror in vehicles.

Spherical mirrors are the mirrors having curved surfaces that are painted on one of the sides. Spherical mirrors in which inward surfaces are painted are known as convex mirrors, while the spherical mirrors in which outward surfaces are painted are known as concave mirrors. Concave mirrors are also known as a converging mirror since the rays converge after falling on the concave mirror, while the convex mirrors are known as diverging mirrors as the rays diverge after falling on the convex mirror.

Parabolic mirrors.  They produce a wide parallel beam or converge a large beam of light to a point. They are widely used in making car headlights or in spotlights.

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 In this subtopic, we will learn about image formation by concave and convex mirrors.

Parts of a spherical mirror.

1. Centre of curvature (C) – this is the centre of the sphere of which the mirror is part of. The centre itself is called the pole (P).
2. Principal axis – this is the line joining the centre of curvature (C) to the pole (P).3. Principal focus (F) – is a point on the principal axis through which a ray is reflected when it hits a concave mirror.

 In a convex mirror the ray is reflected and appears to originate from the point. F is virtual for a convex mirror while it is real for a concave mirror.

3. Radius of curvature (r) – this is the distance from the pole to the centre of curvature. The distance from the pole to the principal focus is called the focal length (f).

 Guidelines for Rays Falling on the Concave and Convex Mirrors

1. When a ray strikes concave or convex mirrors obliquely at its pole, it is reflected obliquely.
2. When a ray, parallel to principal axis strikes concave or convex mirrors, the reflected ray passes through the focus on the principal axis.
3. When a ray, passing through focus strikes concave or convex mirrors, the reflected ray will pass parallel to the principal axis.
4. A ray passing through the center of curvature of the spherical mirror will retrace its path after reflection.