I am in the first steps of learning electronics as a hobby, but I always encounter a lot of confusing things that need to be explained. For example, in a simple electronic circuit that contains a resistance (300 ohms), a LED, and a 9-volt battery. To calculate the current in this circuit according to Ohm's law. I =V/R, I = 9/300 = 0,03 mA. But when making measurements on the circuit, the value of the current is slightly different from the result of the calculation. What I want to know is that the reason for the difference is because we did't take in account the resistance value of the LED? In real circuits analysis we have to take into account the resistance value of electronic components (other than resistors) when calculating the value of the current,? and how is this done in practice?

Thanks in advance for your appreciated HELP.

Walid