Types of Mirrors

Mirrors are any surface that reflects most types of incident light rays that hit their surface. They can have plane or curved surfaces. Based on this, we divide them into two types: plane mirrors and spherical mirrors. Plane mirrors have flat, polished reflecting surfaces. Spherical mirrors have curved reflecting surfaces. The spherical reflecting surfaces are either concave or convex mirrors. It depends on the curvature of the mirror. Mirrors that bulge outwards are convex mirrors and the reflecting mirrors that bulge inwards are called concave mirrors. This is the most basic explanation of what the concave and convex mirrors are.

Notable aspects of a spherical mirror

A spherical mirror will have - 

• Pole: the midpoint of the spherical mirror from which we make all measurements. Capital P represents it. Aperture: An aperture of a mirror is the point from which light reflects. It also gives an idea about the size of the mirror.
• Principal axis: It is an imaginary line that passes through the optical centre and from the centre of curvature of a spherical mirror. This line forms the basis for all the measurements.
• Focus: Any given point on the principal axis where light rays are parallel to the principal axis will converge or appear to converge after getting reflected from the mirror is called focus.
• Principal Focus: The Principal Focus or the Focal Point is on the mirror’s axis. It is where the rays of light, parallel to the principal axis, converge or diverge after reflection.
• Centre of Curvature: it is the point in the centre of the mirror surface that passes through the curve of the mirror and has the same tangent and curvature at that point. The capital letter C represents it.
• The radius of Curvature: It is the linear distance between the pole and the centre of curvature. The capital letter R represents it.

Ray diagram for mirrors

When two rays intersect or appear to intersect, curved mirrors form images. There are four important rays used in ray diagrams, these are - 

• Reflected ray - A ray passing through C or appearing to pass through C
• Parallel ray - a ray parallel and close to the principal axis.
• Focal ray - A ray passing through the principal focus F or appearing to pass through F
• Incident ray - A ray incident at the pole of the mirror.

Concave Mirrors

A concave mirror caves inwards in the middle. Here the light converges to only one prime focus point, hence it is also called a converging mirror. These mirrors focus light. The image formed by the concave mirror depends on the object's position. It will differ in size and be either virtual or real. The image will be either erect, magnified, or inverted. We will either enlarge or reduce its size. 

Image formation by concave mirrors

A concave mirror forms an image that is either real or virtual, small or large. This depends on the source's position and the reflecting point.

Let us examine the Concave mirror ray Diagram - 

The image formed by a concave mirror depends on the object’s position:

• Beyond the center of curvature: Real, inverted, and smaller than the object.
• At the center of curvature: Real, inverted, and the same size as the object.
• Between the center and focus: Real, inverted, and magnified.
• At the focus: No image is formed; rays converge at infinity.
• Between the focus and mirror: Virtual, upright, and magnified.

Application of Concave mirrors

• As a collector of radiation for solar heating devices such as solar ovens, 
• As a reflecting mirror behind the projector lamp
• In floodlights and torches
• As reflecting mirrors in car headlights and searchlights.
• As a dentist’s mirror, make-up or shaving mirror and satellite dishes.

Convex Mirrors

A convex mirror has a reflective surface towards the outside of the bulge, towards the light. It deflects light outwards, diverging the rays. So, we call it a diverging mirror. The object's position and the light's reflection determine the image. It is erect, virtual, and smaller than the object.

Image formation by convex mirrors

The image gets larger as the object comes closer to the mirror.

Convex mirrors always form a virtual, upright, and diminished image, regardless of the object’s position. This property makes them ideal for applications like rearview mirrors in vehicles.

Applications of Convex mirrors

• Security mirrors in office spaces, ATM vestibules, complexes, residential buildings, etc., use it.
• Manufacturers use it in the rearview mirrors of vehicles.
• Manufacturers use it in magnifying glasses, sunglasses, and street light reflectors.
• Researchers use it in electronic microscopes, astronomical telescopes, visual bomb detectors, etc.

The distance measured in the direction of incident rays is positive. In the opposite direction, it is negative. We measure all distances from the pole to calculate the object's or image's positions. 

Difference between concave and convex mirror

Properties of Concave and Convex Mirrors

1. Concave Mirror:
   • Light converges to a focal point.
   • Can form real, inverted images or virtual, upright images.
   • Magnification depends on the object's distance from the mirror.
2. Convex Mirror:
   • Light diverges, appearing to come from a virtual focal point behind the mirror.
   • Always forms virtual, upright, and diminished images.
   • Provides a wider field of view.

Mathematical Representation

Mirror Equation:

1/f = 1/u + 1/v

Where:

f: Focal length of the mirror

u: Object distance from the mirror

v: Image distance from the mirror

Magnification Formula:

M = -v/u

Explanation of magnification:

M: Magnification of the image

-v/u: Negative value indicates an inverted image.

Positive value indicates an upright image.