Old query.
A) Is it possible to determine the frequency of a device without using oscilloscope?
B) Is snubber circuit a right choice to protect the circuit from circuit breaking.
C) capacitor is placed in fan it is a necessary component can any one explain how it works?
+++++++
A. It depends, if you are referring to a specific device like a 555 timer the you'll be able to get its frequency without using an oscilloscope. The computed value is an approximation of the actual using an oscilloscope. If you will ask why it's not exact then you'll have to ask Steve about leakage current and tolerance of components.
B) It depends on the circuit you are trying to protect. Other than a snubber, you may consider using a varistor.
C) A fan is basically an inductor. When power is removed, the inductor's current will start to decay very fast and will produce very high voltage spike that will most likely destroy the wire laminations of the coil's wire and short-circuit itself. A capacitor cannot charge instantaneoulsy, so if you place it in parallel to the coil you will have control over the voltage spikes. It's a simple and straight-forward method of protection but it there are some other methods of choice.