An object is placed 15 cm in front of a convex lens of focal length 25 cm. The image distance will be ______. 

The correct answer is -37.5 cm.

Key Points

• To find the image distance (v) for an object placed at a distance (u) in front of a convex lens, we use the lens formula: 1/f = 1/v - 1/u, where f is the focal length.
• Given values: f = +25 cm (positive for convex lens), u = -15 cm (negative as the object is placed in front of the lens).
• Substitute the values in the formula: 1/25 = 1/v - 1/(-15).
• Solving the equation: 1/25 = 1/v + 1/15.
• Find a common denominator and simplify: 1/25 = (15 + 25)/(25 * 15).
• Resulting in 1/v = -1/37.5.
• Therefore, v = -37.5 cm.
• This indicates that the image is formed at a distance of 37.5 cm on the same side as the object (virtual image).

 Additional Information

• Convex Lens
  • A convex lens is a converging lens that bends light rays inward.
  • It can form both real and virtual images depending on the position of the object.
  • Convex lenses are commonly used in magnifying glasses, cameras, and corrective lenses.
• Image Formation
  • The nature of the image (real or virtual) depends on the position of the object relative to the focal length.
  • If the object is placed inside the focal length of a convex lens, the image formed is virtual, upright, and enlarged.
  • If the object is placed beyond the focal length, the image is real and inverted.