Question

a handle or a knob is fixed at the free end of a door why

Answer 1

a handle or a knob is fixed at the free end of a door so that we may open and close the door easily.If you place the knob in the centre
of the door, you won’t get enough
leverage to open it easily. Also, it
would be difficult to lock as part of
the mechanism sits in the door
frame - a long way from the centre.
You can find out more about fitting
doors by visiting the Wonkee
Donkee XL Joinery door
information section.

Answer 2

The purpose of a door handle is to provide a point of force to pull open an un-latched door by hand. In the case of a latched door, using the door handle to operate the latch and door with one hand without repositioning the hand is more efficient than other alternatives. And placing a latch on the edge opposite the hinged edge creates a type 3 lever, which provides a significant mechanical advantage for the latch.