Electric Circuits: Current, Voltage and Resistance

<h3>Building a circuit</h3><p>An <strong>electric circuit</strong> is a complete, unbroken path around which <strong>current</strong> can flow. A simple circuit has:</p><ul><li>A <strong>source</strong> of electrical energy (a cell or battery).</li><li><strong>Conducting wires</strong> to carry the current.</li><li>A <strong>switch</strong> to open or close the path.</li><li>A <strong>component</strong> such as a bulb or buzzer.</li></ul><h3>Three key quantities</h3><ul><li><strong>Current (I):</strong> the rate of flow of charge, measured in amperes (A).</li><li><strong>Voltage (V):</strong> the electrical push from the source, measured in volts (V).</li><li><strong>Resistance (R):</strong> the opposition to current, measured in ohms (&Omega;).</li></ul><p>These are related: for a fixed voltage, a higher resistance lets <strong>less</strong> current flow.</p><h3>Series and parallel</h3><p>In a <strong>series circuit</strong> the components are in a single loop, so the same current flows through each one. In a <strong>parallel circuit</strong> the components are on separate branches, so each branch can work even if another is switched off.</p><div class="callout"><strong>Kenyan context:</strong> House wiring in Kenya uses parallel circuits. That is why you can switch off the sitting-room light while the kitchen bulb stays on &mdash; each room is on its own branch, all sharing the same mains voltage from Kenya Power.</div>