And if we measure the current in this circuit.
Figure 27. The measured current in this figure is 3.03 mA.
Now, let us calculate the value of the resistor. We have a 9 V battery, the voltage on
the LED is 1.878 V, so the voltage on the resistor is:
9 𝑉 − 1. 878 𝑉 = 7. 122 𝑉
Now, let us use Ohm’s law:
𝑅 =
𝑉
𝐼
𝑅 =
7.122 𝑉
20 𝑚𝐴
= 356. 1 Ω
And the closest standard value is 330 Ω.
Now, let us build the circuit again using a 330 Ω resistor and measure the forward
voltage again and the current.
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