Reflection of Light by Spherical Mirrors – Class 12 | Chapter – 9 | Physics Short Notes Series PDF for NEET & JEE

Reflection of Light by Spherical Mirrors: Spherical mirrors are mirrors that have a curved surface that is shaped like a portion of a sphere. There are two types of spherical mirrors: concave mirrors and convex mirrors. When light strikes a spherical mirror, it can be reflected in a specific way depending on the type of mirror and the position of the object relative to the mirror.

The formation of images by spherical mirrors can be determined using the laws of reflection and geometry. The size, position, and nature of the image depend on the object distance, image distance, and focal length of the mirror. The equations that relate these quantities are known as mirror formulas. The mirror formulas can be used to calculate the image distance and magnification of the image formed by a spherical mirror.

Types of Spherical Mirrors

Spherical mirrors are of two types, and they are classified as follows:

Types of Spherical Mirrors

  • Concave mirrors: A concave mirror is a mirror with a curved surface that bulges inward. When a beam of light strikes a concave mirror, the reflected rays converge at a point in front of the mirror called the focus. This point is located along the principal axis, which is an imaginary line that passes through the center of curvature (the center of the sphere that the mirror is a portion of) and the center of the mirror. The distance between the focus and the mirror is the focal length (f) of the mirror. The image formed by a concave mirror can be real or virtual, depending on the position of the object.
  • Convex mirrors: A convex mirror is a mirror with a curved surface that bulges outward. When a beam of light strikes a convex mirror, the reflected rays diverge as if they are coming from a point behind the mirror. This point is also located along the principal axis, but behind the mirror. The image formed by a convex mirror is always virtual and smaller than the object.

Structure of Spherical Mirrors

Spherical mirrors are curved mirrors that have a spherical shape. They can be either concave or convex depending on the curvature of their surface. The structure of a spherical mirror includes the following parts:

  • Center of curvature: The center of curvature of a spherical mirror is the center of the sphere from which the mirror is made. It is the point at which the mirror would intersect if it were extended all the way around to form a complete sphere.
  • Radius of curvature: The radius of curvature is the distance between the center of curvature and the surface of the mirror. It is half the diameter of the sphere from which the mirror is made.
  • Pole: The pole is the point on the mirror’s surface that is equidistant from the center of curvature. It is the point where the principal axis intersects the mirror.
  • Principal axis: The principal axis is an imaginary line that passes through the center of curvature and the pole of the mirror. It is a reference line used in determining the location and size of the image formed by the mirror.
  • Focal point: The focal point is the point on the principal axis where parallel rays of light converge or appear to diverge after reflection by the mirror. For a concave mirror, the focal point is located in front of the mirror, while for a convex mirror, the focal point is located behind the mirror.
  • Focal length: The focal length is the distance between the focal point and the pole of the mirror. It is the distance at which an object must be placed in front of the mirror to form a sharp image.

Uses of Spherical Mirrors

Spherical mirrors have a variety of uses in everyday life, as well as in scientific and industrial applications. Some common uses of spherical mirrors include:

  • Optical telescopes: Spherical mirrors are used in telescopes to reflect and focus light from distant objects. They are commonly used in reflecting telescopes, where the curved mirror is the primary optical element that gathers and focuses light onto a detector or eyepiece.
  • Automobile headlights: Spherical mirrors are used in automobile headlights to reflect light and produce a beam of light with a specific pattern that illuminates the road ahead. Reflectors in headlights may be either convex or concave depending on the specific requirements of the application.
  • Dental mirrors: Spherical mirrors are used in dentistry to provide a magnified and well-lit view of the patient’s teeth. The mirrors reflect light from an external source onto the tooth, allowing the dentist to see the tooth from multiple angles.
  • Rearview mirrors: Spherical mirrors are commonly used in automobile rearview mirrors to provide a wide-angle view of the area behind the car. Convex mirrors are typically used for this purpose, as they provide a wider field of view than flat mirrors.
  • Projectors: Spherical mirrors are used in projectors to reflect and focus light onto a screen. They are commonly used in overhead projectors, where the mirror is used to reflect the light from the bulb onto a transparency or slide.
  • Solar power plants: Spherical mirrors are used in solar power plants to reflect and focus sunlight onto a central tower. The concentrated sunlight heats a fluid, which is then used to generate electricity.

Applications of Reflection of Light by Spherical Mirrors

The reflection of light by spherical mirrors has many practical applications in various fields, including:

  • Optics: Spherical mirrors are used in the design and construction of optical instruments such as telescopes, microscopes, and laser cavities. The reflective properties of spherical mirrors are used to focus, collimate, or reflect light in precise ways.
  • Dentistry: Concave mirrors are used in dentistry to examine and treat teeth. They are used to reflect light onto a specific area of the mouth, making it easier to see and work on.
  • Automotive: Spherical mirrors are used in automobiles as rearview mirrors, side mirrors, and wing mirrors. These mirrors allow drivers to see behind and to the sides of the car, helping them to navigate traffic and avoid accidents.
  • Lighting: Spherical mirrors are used in lighting fixtures to reflect and direct light. They are used to create focused and directional lighting in theaters, museums, and other public spaces.
  • Solar power: Spherical mirrors are used in solar power plants to concentrate sunlight onto a small area, generating heat that can be used to produce electricity.
  • Astronomy: Spherical mirrors are used in telescopes and other astronomical instruments to gather and focus light from distant celestial objects. The reflective properties of spherical mirrors allow astronomers to study the properties and behavior of stars, galaxies, and other celestial objects.

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By Team Learning Mantras