"You will see arks & sparks at the commutator end. Also the Brushes have small dime size access areas for brush replacement."
The original post was: "how can we recognize d.c motor and induction motor just by watching it ? what is rating of fan motor?
Not all DC motors are so small as to have "dime sized" covers over the brushes, and not all dime-sized brush covers are on DC motors (e.g., your 120vac Skil-Saw).
There is no single / set standard for appearance of any category of electric motor. Nameplate data is the best suggestion; but, without a nameplate, either investigation of the application/installation , or , Education is your best bet.
You'll recognize everything from tiny skeletal "C"-frame motors to synchronous motors in no time ... and understand how to troubleshoot & repair them as well!
Air-handling is one of the most demanding applications for a motor (unbeknownst to many). The rating of a fan motor depends on how much air it is being asked to push, and under what conditions ... i.e., through duct-work, under pressure, etc.
Any additional specifics in the post will bring you much better responses....
