To determine the focal length of a convex lens by obtaining a sharp image of a distant object, the following steps were suggested which are not in proper sequence : I. Hold the lens between the object and the screen. II. Adjust the position of the lens to form a sharp image. III. Select a suitable distant object. IV. Measure the distance between the lens and the screen. The correct sequence of steps to determine the focal length of the lens is

To determine the focal length of a convex lens using a distant object, the experiment must follow a logical, step-by-step procedure:

1. Step III (Select a suitable distant object): First, a well-illuminated distant object (such as a tree or a building) must be selected. Light rays coming from a distant object are parallel to the principal axis.
2. Step I (Hold the lens between the object and the screen): The convex lens is placed on a stand and positioned between the selected distant object and a screen.
3. Step II (Adjust the position of the lens to form a sharp image): The position of the lens is adjusted back and forth relative to the screen until a sharp, clear, and inverted image of the distant object is focused on the screen.
4. Step IV (Measure the distance between the lens and the screen): Once the sharpest image is obtained, the distance between the optical center of the lens and the screen is measured using a meter scale. This distance represents the focal length ($f$) of the convex lens.

• Option A (III, I, II, IV) is correct because it represents this exact logical sequence.
• Option B is incorrect because it suggests measuring the distance (IV) before adjusting the lens to form a sharp image (II).
• Option C is incorrect because it suggests measuring the distance (IV) before even holding the lens in place (I) or focusing the image.
• Option D is incorrect because it starts with holding the lens (I) before selecting a suitable distant object (III).