An imaginary straight line passing through the pole and the centre of curvature of a spherical mirror is called as ______

The correct answer is principal axis.

Key Points

• The principal axis is an imaginary line passing through the pole and the centre of curvature of a spherical mirror.
• It is used as the reference line for measuring the angles of incident and reflected rays in optics.
• The point where the principal axis meets the mirror surface is known as the pole (P) of the mirror.
• The principal axis helps in determining the focal length and radius of curvature of the mirror.

Additional Information

• Centre of Curvature
  • The centre of curvature is the center of the sphere from which the spherical mirror is a part.
  • It is denoted by the letter C.
• Focal Point
  • The focal point, also known as the focus, is the point where parallel rays of light either converge or appear to diverge after reflecting from the mirror.
  • It is denoted by the letter F.
• Focal Length
  • The focal length is the distance between the pole and the focal point of the mirror.
  • It is denoted by the letter f.
• Radius of Curvature
  • The radius of curvature is the distance between the pole and the centre of curvature.
  • It is denoted by the letter R and is equal to twice the focal length (R = 2f).