Challenge 1 of 5Right first time: 0
Current:
The job
I = (Vbattery − VLED) ÷ R
An LED uses up a fixed voltage. The resistor takes whatever voltage is left over, and that sets how many electrons flow each second. Keep the current between 10 and 20 mA.
Show me how to rearrange it
R = (Vbattery − VLED) ÷ I. Use amps, so 15 mA is 0.015 A. Then pick the closest resistor that keeps you in the safe zone.