Concave Mirror – Class 12 | Chapter – 9 | Physics Short Notes Series PDF for NEET & JEE

Concave Mirror: A concave mirror is a type of spherical mirror that curves inward like a bowl. It is also known as a converging mirror because it converges or focuses light that falls on its surface. The reflective surface of a concave mirror is on the inside of the sphere that the mirror is a part of. When parallel light rays fall on a concave mirror, they are reflected and converge to a point known as the focal point, located in front of the mirror.

The focal length of a concave mirror is half the radius of curvature of the mirror, as given by the formula:

f = R/2

where f is the focal length and R is the radius of curvature. If an object is placed beyond the focal point of a concave mirror, it produces a real, inverted image that is smaller than the object. The image is located between the focal point and the mirror’s surface. If the object is placed at the focal point, the reflected rays will be parallel and the image will be formed at infinity. If the object is placed between the mirror and the focal point, the image will be virtual, upright, and magnified.

Characteristics of a Concave Mirror

The characteristics of a concave mirror include:

  • Converging mirror: A concave mirror is also known as a converging mirror because it converges or focuses light that falls on its surface.
  • Reflective surface: The reflective surface of a concave mirror is on the inside of the sphere that the mirror is a part of.
  • Focal point: When parallel light rays fall on a concave mirror, they are reflected and converge to a point known as the focal point, located in front of the mirror.
  • Focal length: The distance between the focal point and the center of the mirror is known as the focal length. The focal length of a concave mirror is half the radius of curvature of the mirror, as given by the formula f = R/2.
  • Image formation: The image formed by a concave mirror depends on the position of the object with respect to the focal point. If the object is located beyond the focal point, a real, inverted image is formed. If the object is located at the focal point, no image is formed. If the object is located between the focal point and the mirror, a virtual, upright, and magnified image is formed.
  • Magnification: The magnification produced by a concave mirror depends on the position of the object. If the object is beyond the focal point, the image is smaller than the object. If the object is between the focal point and the mirror, the image is larger than the object.
  • Applications: Concave mirrors have a wide range of applications, including in telescopes, microscopes, car headlights, solar collectors, and medical equipment.

Uses of a Concave Mirror

Concave mirrors have a wide range of applications due to their ability to focus and manipulate light. Some of the uses of a concave mirror include:

  • Telescopes: Concave mirrors are used in reflecting telescopes as the primary optical element to collect and focus light from distant objects. The curvature of the mirror allows for a wider field of view and improved image quality.
  • Microscopes: In microscopes, concave mirrors are used to direct light onto the object being observed. The mirror helps to illuminate the object and provide a clear view for the observer.
  • Car headlights: Concave mirrors are used in car headlights to produce a powerful beam of light that can illuminate the road ahead. The mirror focuses the light from the bulb onto a specific area, allowing the driver to see more clearly in the dark.
  • Solar collectors: Concave mirrors are used in solar collectors to concentrate sunlight onto a small area, which is used to heat a fluid. The heated fluid can then be used to generate electricity or provide heat for homes and businesses.
  • Medical equipment: Concave mirrors are used in medical equipment such as dental mirrors and endoscopes to provide a magnified view of the patient’s teeth or internal organs. The mirror helps to provide a clear image for the medical professional to examine.
  • Reflective optics: Concave mirrors are also used in reflective optics, such as laser and projector systems, to reflect and focus light onto a specific area.

Image Formation by Concave Mirror

The image formation by a concave mirror depends on the position of the object with respect to the mirror. The image formed can be either real or virtual, upright or inverted, and magnified or diminished.

  • Object beyond the center of curvature: When the object is placed beyond the center of curvature (C), a real and inverted image is formed between the focus (F) and the center of curvature (C). The size of the image depends on the position of the object. If the object is placed far from the mirror, the image will be small. If the object is placed closer to the mirror, the image will be larger.
  • Object at the center of curvature: When the object is placed at the center of curvature (C), a real and inverted image is formed at the center of curvature. The size of the image is the same as the size of the object.
  • Object between the center of curvature and the focus: When the object is placed between the center of curvature (C) and the focus (F), a real and inverted image is formed beyond the center of curvature. The size of the image is smaller than the size of the object.
  • Object at the focus: When the object is placed at the focus (F), no image is formed as the reflected rays are parallel and do not converge.
  • Object between the focus and the mirror: When the object is placed between the focus (F) and the mirror, a virtual and upright image is formed behind the mirror. The image is magnified and is larger than the size of the object.

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By Team Learning Mantras