Practical skills Study Guide

The behaviour of springs under load is an important concept in physics, often investigated by measuring their extension when different forces are applied. A key principle is Hooke's Law, which states that the extension of an elastic object is directly proportional to the force applied to it, as long as the elastic limit is not exceeded. This means if you double the force, you double the extension. This proportionality results in a straight line graph when force is plotted against extension, passing through the origin. The gradient of this line represents the spring constant, 'k', measured in Newtons per metre (N/m). A larger spring constant indicates a stiffer spring. However, if too much force is applied, the spring will exceed its elastic limit. Beyond this point, it will not return to its original length when the force is removed, and Hooke's Law no longer applies. In an investigation, the independent variable is the force applied (usually by adding masses), and the dependent variable is the extension of the spring. Control variables include the type of spring used and the temperature. Safety precautions are crucial, such as securing the clamp stand, ensuring weights do not fall, and wearing eye protection. The apparatus typically includes a spring, a clamp stand, a ruler or metre rule, a set of known masses, and a G-clamp to secure the stand. Measuring from the same point on the spring consistently is vital for accuracy. The extension is calculated by subtracting the spring's original length (when no mass is attached) from its stretched length with a mass attached.

To understand how different components behave in an electrical circuit, we can investigate their characteristics by measuring the current flowing through them and the potential difference (voltage) across them. This is often done by constructing a simple series circuit for current measurements and adding a parallel connection for potential difference measurements. The key components typically include a power supply (such as a cell or battery pack), an ammeter to measure current (always connected in series), a voltmeter to measure potential difference (always connected in parallel across the component), and the component under investigation (e.g., a resistor, a filament lamp, or a diode).

Firstly, connect the ammeter in series with the component to measure the current. Then, connect the voltmeter in parallel across the component. The independent variable is usually the potential difference supplied by the power supply (often controlled by a variable resistor or by changing the number of cells), while the dependent variables are the current and potential difference across the component. Control variables include temperature, which can affect resistance, and the specific component being tested. By varying the potential difference and recording the corresponding current and potential difference values, a set of data can be collected. This data can then be plotted on a graph with potential difference (V) on the x-axis and current (I) on the y-axis, providing a visual representation of the component's characteristic. For a fixed resistor, this graph will be a straight line through the origin, indicating constant resistance (Ohm's Law). For a filament lamp, the graph will curve, showing an increase in resistance as temperature rises. For a diode, current only flows significantly in one direction, and only after a certain potential difference is reached.