Questions | 5 |

Topics | Battery Configurations, Inductors, Ohm's Law, Resistance, Transistors |

Batteries can be connected together in various combinations to increase their total voltage and/or total current. Connecting batteries in **series** combines their voltage while keeping their current the same, connecting batteries in **parallel** combines their current while keeping their voltage the same, and using a **series-parallel** configuration, half the batteries can be connected in series and half in parallel to combine both voltage and current.

An inductor is coiled wire that stores electric energy in the form of magnetic energy and resists changes in the electric current flowing through it. If current is increasing, the inductor produces a voltage that slows the increase and, if current is decreasing, the magnetic energy in the coil opposes the decrease to keep the current flowing longer. In contrast to capacitors, inductors allow DC to pass easily but resist the flow of AC.

Ohm's law specifies the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit: **V = IR**.

Resistance is opposition to the flow of current and is measured in **ohms** (Ω). One ohm is defined as the amount of resistance that will allow one ampere of current to flow if one volt of voltage is applied. As resistance increases, current decreases as resistance and current are inversely proportional.

The transistor is the foundation of modern electronic devices. It is made entirely from semiconductor material (making it a **solid state** **device**) and can serve many different functions in a circuit including acting as a switch, amplifier, or current regulator. A transistor works by allowing a small amount of current applied at the **base** to control general current flow from **collector** to **emitter** through the transistor.