Question

Where should an object is placed in front of a convex lens to get a real image of the size of the object?

• A. At the principal focus of the lens.
• B. At twice the focal length.
• C. At infinity.
• D. Between the optical center of the lens and its principal focus.

Answer 1

The correct option is B

At twice the focal length.

Explanation for correct option

Option B,

When the object is at $2f$(twice the focal length )

1. The image is formed at $2f$.
2. A real inverted image is formed of the same size as that of the object.

Option B is correct.

Explanation of incorrect options

Option A,

When the object is at $f$(principal focus of the lens)

1. The image is formed at infinity.
2. A real, inverted, and magnified image is formed.

Option A is incorrect.

Option C,

When the object is at infinity,

1. The image is formed at the focus.
2. A real, inverted, and diminished image is formed.

Option C is incorrect.

Option D,

When the object is between the optical center of the lens and its principal focus

1. The image is formed between the optical center of the lens and its principal focus.
2. A virtual, erect, and enlarged image is formed.
3. The image is formed on the same side as the object.

Option D is incorrect.

Therefore, option B is correct.