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Voltage, current and resistance
Voltage is a potential difference between two points. Current is the rate of flow of electric charge. Resistance describes how a component opposes current under the conditions of the model. For an ohmic resistor, V = I × R.
Keep units straight: volts, amperes and ohms. Milliamperes are thousandths of an ampere. This lesson uses a mathematical battery-and-resistor model, not an instruction to connect arbitrary components to a power source.
Worked example
An ideal 6 V source across 300 Ω gives I = 6/300 = 0.02 A = 20 mA. Resistor power is V × I = 0.12 W.
Try it yourself
Draw an ideal circuit and calculate current for 3 V across 150 Ω.
Check your understanding
How much current is 6 V across 300 Ω?
6/300 = 0.02 A, and multiplying amperes by 1000 gives milliamperes.
References and further reading
Lessons and examples are original introductory material. These references offer further study; their material is not included as a copied course.
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