I don't understand our professor's explanation for the answer to this problem:
An LED is connected in series to a 150ohms pull up resistor and a MOSFET with drain-source resistance of 3ohms. The Pull up resistor is connected to a 5V source and the MOSFET is connected to ground (say MOSFET is turned on i.e. the gate). Now if there is a 2V drop across the LED, what is the current flowing through the LED.
I calculated the LED's resistance to be 102ohms giving the current through the LED to be 19.6 mA (which is correct).
But my professor says that the LED has no resistance at all and that my method of calculation is wrong (despite there being a voltage drop). And he said something about thevenin resistance which I did not understand.
Do you know what he is talking about?