Electricity Study Guide

Electrical circuits are fundamental to understanding how electricity behaves. The design of a circuit allows us to control and observe specific electrical effects, such as current flow, potential difference (voltage), and resistance. Simple circuits typically consist of a power source (like a battery), a component (such as a bulb or resistor), and connecting wires. To investigate current, an ammeter is always connected in series with the component. This means the current flows through the ammeter, allowing it to measure the rate of charge flow through that part of the circuit. To measure potential difference across a component, a voltmeter is connected in parallel. This places the voltmeter's terminals on either side of the component, allowing it to measure the energy transferred per unit charge as it passes through the component. Resistances can be connected in series or parallel, each configuration having distinct effects on the total resistance and how current and voltage are distributed. For instance, in a series circuit, components are connected one after another, so the current is the same everywhere, but the potential difference is divided among them. In contrast, in a parallel circuit, components are connected across the same two points, meaning they each have the same potential difference across them, but the total current splits among them according to their resistances. By constructing these circuits meticulously, ensuring secure connections and correct meter placement, we can systematically explore these electrical relationships and verify fundamental laws like Ohm's Law and the principles of series and parallel circuits.

In electrical circuits, components can be classified as either linear or non-linear based on how their current (I) changes in response to varying voltage (V) across them. This relationship is often explored and visualised using an I-V graph, where current is plotted on the y-axis and voltage on the x-axis.

A circuit element is considered linear if its resistance remains constant, regardless of the voltage applied or the current flowing through it. According to Ohm's Law (V = IR), if R is constant, then current is directly proportional to voltage (I = V/R). When plotted on an I-V graph, a linear component will produce a straight line passing through the origin. The gradient of this line is constant and is equal to 1/R (the reciprocal of resistance).

Examples of linear components include fixed resistors, provided their temperature does not change significantly. The characteristic straight line on an I-V graph indicates a constant resistance, meaning that doubling the voltage across it will double the current flowing through it.

On the other hand, a circuit element is non-linear if its resistance changes with the applied voltage or current. This means that current is not directly proportional to voltage. When plotted on an I-V graph, a non-linear component will produce a curved line. The gradient of this curve changes, indicating that the resistance is not constant but varies depending on the operating conditions.

Examples of non-linear components include filament lamps and diodes. For a filament lamp, as voltage increases, the filament heats up, causing its resistance to increase. On an I-V graph, this appears as a curve that becomes less steep at higher voltages (meaning resistance is increasing). For a diode, current flows almost exclusively in one direction (forward bias) after a certain threshold voltage, and resistance is very high in the opposite direction (reverse bias). Its I-V graph shows a very distinctive non-linear shape.

By analysing the shape of the I-V graph, specifically whether it is a straight line through the origin or a curve, we can determine whether a circuit element exhibits linear or non-linear behaviour. This understanding is fundamental to designing and analysing electronic circuits.