A convex lens forms an image of an object placed 30 cm away. The image is formed at 60 cm on the other side. The magnification is:

Correct option is A

The correct answer is (a) −2

Explanation:

• According to the standard sign convention, the object distance (u) is taken as negative because the object is placed on the left side of the lens.
Thus, u = −30 cm.

• The image is formed on the other side (right side) of the convex lens, so the image distance (v) is positive.
Thus, v = +60 cm.

• The formula for linear magnification for a lens is:
m = v / u

• Substituting the values:
m = +60 / −30

• Therefore, m = −2.

Information Booster:

• A negative magnification indicates that the image formed is real and inverted.

• The magnitude 2 means the image is twice the size of the object (magnified).

• Convex lenses can form real and inverted images on the opposite side of the lens.

Additional Knowledge:

−1/2 (Option b)
• This would occur if the object were at 60 cm and the image formed at 30 cm, producing a diminished image.

+1/2 (Option c)
• A positive magnification indicates a virtual and erect image, typically formed by a concave lens.

+2 (Option d)
• This indicates a virtual, erect, and magnified image, which occurs when the object is placed between the optical centre and the principal focus of a convex lens.