To determine the position sb of the image of an object placed in air on the axis of the rod infinitely far from the left end of the rod, we need to consider the thin lens formula:
1/f = 1/sa + 1/sb
where f is the focal length of the lens, sa is the object distance, and sb is the image distance.
Since the object is placed infinitely far from the left end of the rod, sa can be considered as approaching infinity. This means that 1/sa approaches zero.
In this case, the thin lens formula simplifies to:
1/f = 0 + 1/sb
Solving for sb, we find:
sb = 1/f
To express the answer in centimeters, we need to know the value of the focal length f in centimeters. Once we have that information, we can substitute it into the equation to calculate the position sb of the image.