Beginner · 10 min
Simple electric circuits
Use voltage, current, and resistance to calculate values in a simple circuit.
A complete path
Electric current is a flow of electric charge, measured in amperes (A). A simple battery circuit needs a complete conducting path for a steady current. Voltage, measured in volts (V), describes the energy transferred per unit charge between two points. Resistance, measured in ohms (Ω), describes how strongly a component opposes current. An open switch breaks the path and stops the steady current in a simple series circuit.
Worked example
In a diagram with one battery, one resistor, and a switch in series, closing the switch completes the path.
Use Ohm's law
For an ohmic resistor at constant temperature, voltage equals current multiplied by resistance: V = I × R. Divide voltage by resistance to find current. At the same voltage, a larger resistance gives a smaller current. These exercises use ideal batteries and resistors, so the stated voltage is the voltage across the resistor. Explore these relationships on paper or in a circuit simulator.
Worked example
A 6 V supply is connected across a 3 Ω resistor. Current = 6 ÷ 3 = 2 A
Interactive experiment
Resistance lab
Keep the voltage at 6 V. Change the resistance and observe the current.
Current
0.6 A
I = 6 / 10 = 0.6 A
Model: an ideal ohmic resistor at constant temperature. At fixed voltage, greater resistance means less current.
Design a circuit on paper
- Draw a complete circuit with a 6 V battery, one 6 Ω resistor, and a closed switch. Calculate the current.
- Replace the resistor in your drawing with a 12 Ω resistor. Calculate the new current and compare it with the first.