Question

If there is a source voltage of 12 volts with a 2.5 volt drop over the LED, and an intended current of 100 mA, what size resistor should be used?

Answer 1

Given:

A voltage source has a voltage of 12 V.

A voltage drop over the LED is 2.5 V.

The current in the circuit is 100 mA.

To find:

The resistance of the resistor should be used.

Step-by-step explanation:

LED is a forward-biased PN junction that emits light. The voltage drop over the LED is 2.5 V.

The voltage source has a voltage of 12 V.

Hence, the total voltage in the circuit = 12 V - 2.5 V = 9.5 V

The resistance of the circuit in the forward biased is almost equal to zero. Let the resistance in the circuit be R.

Thus, the total resistance in the circuit = 0 + R = R

The current in the circuit is = 100 mA = 0.1 A

The resistance R of the circuit can be calculated as:

`R=(V)/(I)`

Here, V is the voltage in the circuit and I is the current in the circuit.

Substituting the values in the above equation, we get:

`\begin{gathered} R=\frac{9.5\text{ V}}{0.1\text{ A}} \\ \\ R=95\text{ }\Omega \end{gathered}`

Final answer:

Hence, a resistor of 95 Ω should be used in the circuit.