Spherical mirror formula relating an object distance ‘u’, image distance ‘v’ and focal length of mirror ‘f’ may be applied to a plane mirror when

CONCEPT:

• Mirror Formula: The following formula is known as the mirror formula, which provided a relationship between focal length (f), image distance (v), and objects distant (u) as shown below

​EXPLANATION:

• Plane Mirror is a part of the infinitely large spherical mirror:

• Since the plane mirror is a part of an infinitely large spherical mirror, therefore the radius of curvature and focal length of the plane mirror is Infinity.
• Spherical mirror formula relating an object distance ‘u’, image distance ‘v’ and focal length of mirror ‘f’ may be applied to a plane mirror when focal length goes to infinity. Therefore option 1 is correct.

Additional Information

Sign convention in mirrors

• All distances are measured from the pole of the mirror.
• The distance measured from the pole (p) to the left side of the mirror is taken as negative.
• The distance measured from the pole (p) to the right side of the mirror is taken as positive.
• The heights measured upwards and perpendicular to the principal axis of the mirror is taken as positive.
• The heights measured downwards and perpendicular to the principal axis of the mirror is taken as negative.