Does power factor vary with load.

www.google.com is a great resource in the quest for information such as this.

http://en.wikipedia.org/wiki/Power_factor

It does vary somewhat , but I really forgot how exactly. There are plenty of online resources you could search GOOGLE " power factors motors under load".

Read this:

http://www.lmphotonics.com/pwrfact.htm

This is a great web site for information and you will find the answer here.

http://www.engineeringtoolbox.com/ worth a look if you have a few hours to spare.

power factor will depend upon load on the circuit with the changing amount of capacitance and inductance of the load devices.

Jananjaya,

The references are good. I'll try to be brief and to the point of your question. With a purely inductive load, the AC voltage reaches its peak 90° ahead of the current. With a purely resistive load, they peak at the same time. A motor has both the magnetizing current (inductive) and the work current (resistive). Unloaded, nearly all the current is magnetizing (only a small amount is doing work, such as overcoming friction, or moving air within the motor). Therefore, an unloaded motor will have a fairly low power factor. As the load on the motor rises towards its full design load, the work current is increasing, so a fully loaded motor can often have a power factor greater than 0.85. Unfortunately, different motor designs will have different characteristics of the work current and magnetizing current (and other loss currents which I have not mentioned). Therefore, each design would have its own curve.

--JMM