Ohm's Law
Voltage is the push that moves current through a circuit. Current is how many charges pass a point each second, and resistance slows that current down.
Hold any two values steady and the third can be calculated. That makes Ohm's Law a fast way to check whether a circuit idea is reasonable before you build it.
Interactive Calculator
Try This Scenario
A flashlight battery supplies 3 volts to a bulb drawing 0.15 amps. Enter those two values and the calculator will solve for the bulb's resistance.
If you then imagine raising resistance while keeping voltage fixed, current drops. That is the practical tradeoff Ohm's Law helps you predict.
Series And Parallel Resistance
Series total: -
Parallel total: -
Resistance Color Code Picker
Choose the first two digit bands, a multiplier, and the tolerance band to decode a resistor instantly.
Read the bands from the end opposite the tolerance band.
Do not ignore the multiplier band. It changes the value dramatically.
The tolerance band tells you the expected variation around the labeled value.