Light

• Spherical Mirror:

  • Centre of curvature: Centre of the sphere of which the spherical mirror is a part
  • Pole: Midpoint of the aperture of the spherical mirror or mirror centre
  • Focus: Where parallel rays (parallel to the principal axis) meet or appear to meet after reflection
  • Principal Axis: Imaginary line that runs through the pole and the center of curvature of a spherical mirror
  • Distance of focus from the pole is half the radius of curvature
• Two types of spherical mirrors:

  1. Convex mirror:

  • Image formed is erect and diminished, behind the mirror
  • Image is always virtual
  • Used as the reflector of a torch, dentist mirror, and in solar furnaces

  2. Concave mirror:

  • Image formed can be erect or inverted, diminished or magnified, behind or in front of the mirror
  • Image can be real or virtual
  • Used as a rear view mirror in vehicles and road safety mirrors
• Sign Conventions for Spherical Mirrors:

  • For concave mirror, f = negative; for convex mirror, f = positive
  • Magnification formula: Magnification = -v/u
  • Refraction Laws: Incident ray, refracted ray, and normal to the interface at incident point are coplanar
  • Refractive index (RI) formula: μ21 = v1/v2
• Differences between a spherical mirror and a lens:

  Spherical Mirror:

  • Image formed by reflection of light
  • Has one focus
  • Centre of curvature is termed as its pole

  Lens:

  • Image formed by refraction of light
  • Has two foci
  • Centre of the lens is termed as its optical centre
• Lens:

  • Optical centre is a point at the centre of the lens, inside the lens and not on the surface
  • Principal axis is the straight line joining the two centers of curvature and the optical centre
  • Focus is where parallel rays meet after refraction
  • Convex lens:
  • Forms virtual and erect images when the object is placed between F1 and the optical centre
  • Image size equals object size when the object is at 2F
  • Concave lens:
  • Forms virtual and erect images at all object positions
• Lens Formula:

  • For concave lens, f = negative; for convex lens, f = positive
  • Lens power is the reciprocal of its focal length, negative for concave lens and positive for convex lens