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The steps followed in determining the focal length of a given convex lens by obtaining a sharp image of a distant object are listed below but they are not in correct order.]
(A) Measure the distance between the lens and screen
(B) Adjust the position of the lens to form a sharp image
(C) Select a suitable distant object
(D) Hold the lens between the object and the screen with its faces parallel to the screen.
What should be the correct sequence of steps ?

a. C,A,D,B
b. C,D,B,A
c. C,A,B,D
d. A,B,C,D

Answer
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Hint: Understand the prerequisites for the experiment. Focal length is defined as the distance between the lens curvature and the focal point of the lens. Focal point is the point where rays meet after refraction via the lens. Read through the options and arrange sequentially.

Complete answer:
In order to perform this experiment, there are some prerequisites to be followed. The experiment should be done in a bright environment and not in dark. For this experiment, you will need a convex lens of standard thickness , a source image and a screen.

Select a suitable distance object first. Keep all the required apparatus on the table , on a straight line , before arranging them accordingly. Now, hold the lens between the object and the screen with its faces parallel to the screen.

After that, adjust the lens position accordingly. Place the screen to the other side of the lens and now start to adjust the lens so that a clear and perfect image is obtained on the screen. Once an inverted and real image of the source is formed on the screen. Now once the image is formed, set the position and find the distance between the lens and the screen. The distance is called the focal distance of the mirror. The Object at infinite distance will always be formed on the focus.

Hence, the correct answer is option (B).

Note: A source object that is kept at infinite distance from the lens, is said to form a virtual and inverted image on the focal point of the lens. The virtual image can be captured on the screen. Make sure that the lens is dust free and doesn't have any cracks as it deters the image formation.