If an object is placed at 25 cm in front of a concave mirror of f

SOLUTION

CONCEPT:

• Concave mirror: The mirror in which the rays converge after falling on it is known as the concave mirror.
  • Concave mirrors are also known as a converging mirror.
  • The focal length of a concave mirror is negative according to the sign convention.
• Mirror Formula: The following formula is known as the mirror formula:

\(\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\)

where,

f = focal length 

v = the distance of the image from the mirror,

u = the distance of the object from the mirror.

CALCULATION:

Given that,

Object distance, u = -25 cm,

Focal length, f = -5 cm

By using the mirror formula:

\(\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\)

⇒ \(~-\frac{1}{5}~=\frac{1}{v}-\frac{1}{25}\Rightarrow \frac{1}{v}=\frac{1}{25}~-\frac{1}{5}\)

⇒ Image distance (v) = -6.25 cm 

So option 1 is correct.

NOTE: 

• The lens formula is applicable to both the concave and convex lens.
• And for all lens object distance is considered as positive
• The sign convention used for the focal length of a concave lens is considered as negative, whereas for the convex lens it's considered as positive