Set a current limit from a 12 V battery: What resistance value is required to limit current to 3.6 mA?

Introduction / Context:
Series resistors are commonly used to limit current to safe or specified levels. Selecting the correct ohmic value protects LEDs, sensors, and test circuits powered from batteries or bench supplies.

Given Data / Assumptions:

• Source voltage V = 12 V.
• Desired current I = 3.6 mA = 0.0036 A.
• Find R for a simple series circuit: R = V / I.

Concept / Approach:
Apply Ohm’s law directly after converting mA to A. Expect a value in the kilo-ohm range since milliampere currents from a double-digit voltage typically require thousands of ohms.

Step-by-Step Solution:

Verification / Alternative check:
Back compute the current with 3.3 kΩ: I ≈ 12 / 3300 ≈ 0.00364 A = 3.64 mA, essentially the target 3.6 mA. This validates the selection within rounding and resistor tolerance ranges (for example, 5 percent E24 values).

Why Other Options Are Wrong:

• 33 kΩ and 22 kΩ: Would undercurrent the load severely (tens to hundreds of microamperes).
• 2.2 kΩ: Would allow I ≈ 5.45 mA, exceeding the limit.

Common Pitfalls:

• Mistaking mA for A and obtaining a result 1000 times too small.
• Ignoring practical resistor series and tolerances when picking the nearest value.

Final Answer:
3.3 kΩ