Application of field effect transistor?

A: Imagine a conductive bar and imagine that if a field or potential is applied it will choke or let more current pass as the field is varied

Reference the two definitions given below, one from IEEE and the other from US Army research document. Web links are found after each....The use of cold FET measurements solves the problemof junction...

The main advantage of the FET is its high input resistance, on the order of 100M ohms or more. Thus, it is a voltage-controlled device, and shows a high degree of isolation between input and output....

bjt is bipolar device whr fet is unipolar....fet is input resistance thts y fet gain is less compared to bjt..... The applications that will prefer bipolar junction transistors to field effect...

for a fet an electric field is establishd by the charge present ,that controls the conduction of the output ckt without the need for direct contact between the controlling & control quantities.