List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining image of a distant object on a screen.

List four precautions which a student should observe while determining

1.	List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining image of a distant object on a screen.
Answer» Solution :The precaution while DETERMINING the focel length of a given convex lens by obtaining image of a distant object on a screen are: (i) A convex lens should be PLACED on the lens holder kept on a optical BENCH at a point 'A'. (ii) The position of the screen is adjusted on the other side of the lens in such a way that a clear and SHARP image of the object is formed on it. (iii) The base of the lens and white screen should be in a line with the measuring scale. (iv) There should not be any obstacle in the path of the convex lens.