Question

What happens to the open circuit if a small fan is connected at point f and the circuit is closed

Answer 1

There's no way to tell.  Without seeing a diagram of the circuit,
I'll need to know much more about it than you've told me.
I don't know anything about the components or power supply
that are in the circuit, and I don't know where point ' f ' is in it.

Right now, even with the copious volume of all the available
information, no answer to your question is possible.