Question

The distance between pole and focus is ...

Answer 1

Answer: The distance between pole and focus is known as the focal length.

Explanation:

In an optical system, the focal length estimates the divergence or convergence of the light rays. The focal length is the length measured in mm of the object in focus placed between the pole and the focus. The focal length of the converging lens is calculated as 1/f= 1/v+ 1/u

Answer 2

Answer:  

The distance between ‘pole and focus’ is termed as focal length.

Solution:

The pole is the real object and the focus is the position where the image of the pole will be formed. So, the distance between the ‘pole and focus’ is equal to the ‘focal length’.  

The ‘focal length’ is defined as the ‘distance’ from the lens to the position where the image is formed. As the focus is produced for lens only, the distance between the pole and lens is ignored and the ‘distance’ between the ‘lens and the focus point’ forms the focal length.