What do you mean by looking at it? Looking on the device or a circuit symbol?
When connected in a circuit, in most cases(in digital circuits), the NMOS would have its source connected directly to GND and the PMOS would have its source connected directly to Vdd.
MOS transistors are not discrete components, so you cant look at datasheet or data book for them. They are integrated ones. If you have the schematic, you can know which is NMOS and which is PMOS. They have different symbols. Source of NMOS are usually connected closer to the GND side while those of PMOS are usually connected closer to VCC or VDD side.
--
Amr Ali www.embedded-tips.blogspot.com
I was asking that is it possible to tell whether a component is pmos or nmos just by looking......'by looking' i mean just by looking at the components(neither the symbols, nor by connecting them in a circuit)
Actually this was asked in an interview, so I thought there must be a way to distinguish between the two just 'by looking'....:!::!::!:
Of course they are - there are thousands of them available as discrete components.
If you are talking about discrete devices then you can only distinguish one from the other by the part number.
If you are looking at the silicon of an IC you can tell PMOS from NMOS because you would be able to see the Nwell for a PMOS if it is a P type substrate, for example.
Mostly, but some are smaller e.g. 2N7000. There are also RF ones as well, low power as well as high power. Mitsubishi for example do power RF ones. I cannot remember parts numbers and I have limited internet access at the moment. I can check tomorrow if you want more information. Agilent do HEMT transistors for RF.