This circuit is that of a simple class A audio amplifier. But with zero distortion, Q1 is a switch in the on or off, so that no load current by the resistance R2. In the best case, the tension in Q1 and the load resistance must be equal to the class-A operation.
A 100K potentiometer (R3) and a 1-megohms resistance (R1) Maker a simple variable-Bias circuit. Plase voltmeter between Drain (D) of Q1 and dissemination of soil and adjust R3 for a meter to half the supply voltage.
Applications using an IRF511 has many project as it is pupola part for build the electronic circuit.
Almost every resistor value can be used for R2, as long as the maximum power and the FET are not exceeded.
A resistor value of 22 to 100 ohm is a good choice for experimentation. For high currents, a heat sink adapted to be used.