Context
Capacitance is one of the fundamental concepts in the study of electricity and electronics. It describes the ability of a body to store electrical charge. This ability is all around us and has wide-ranging applications, from making electronic devices work, to keeping our hearts beating steadily.
Capacitance is defined as the ratio of the amount of charge stored on a conductor to the potential difference (or voltage) across it. It is typically measured in Farads (F). An electronic component that has capacitance is called a capacitor. Capacitors are used in a huge range of electrical and electronic applications, from smoothing the output of power supplies to tuning radios.
To fully understand capacitance, it is important to be familiar with some key concepts, such as electric charge, voltage, current, electric fields and electric potential. It is also useful to understand how these concepts are applied practically in devices such as batteries, cells, electric motors, generators, transformers and electronic devices.
Capacitance plays a vital role in our modern world. Without the ability to store and release electrical energy, many of the conveniences of modern life, such as smart phones, computers and televisions, simply would not be possible. Furthermore, understanding capacitance provides a foundation for studying many other topics in physics and engineering.
For an in-depth exploration of the theory behind Capacitance, we recommend the following resources:
- The textbook “Physics for Scientists and Engineers – with Modern Physics” by Serway and Jewett.
- The Khan Academy website, which has a comprehensive course on electricity and magnetism: https://www.khanacademy.org/science/ap-physics-1/ap-linear-momentum/intro-to-ap-linear-momentum/v/ap-linear-momentum-and-collisions-intro
- The YouTube channel “ElectroBOOM”, which has many clear and engaging videos explaining electrical concepts: https://www.youtube.com/c/ElectroBOOM1
Practical Activity: Building and Investigating a Capacitor
Project Aim
The aim of this project is to build and investigate how a capacitor works. Students will apply their theoretical understanding of capacitance, electric charge, voltage, current and electric potential. Furthermore, the project will touch on the topic of sustainability, with students encouraged to use recycled materials in the construction of their capacitor.
Project Outline
Students will work in groups of 3-5. Throughout the project, students should keep a record of all stages, discussions, calculations and conclusions in the form of a report.
Materials
- Aluminium foil
- Wax paper (or cling film)
- Multimeter
- Power supply (battery or power pack)
- Connecting wires
- Basic stationery (ruler, scissors, pens)
- Materials for a capacitor stand (preferably recycled)
Step-by-step guide
1. Building the Capacitor
1.1: Cut two pieces of aluminium foil into rectangles of equal size. These will form the plates of the capacitor.
1.2: Cut a piece of wax paper slightly larger than the aluminium rectangles. This will be the dielectric separating the plates of the capacitor.
1.3: Assemble the capacitor by placing the wax paper between the two aluminium plates. Carefully roll the three layers together. Ensure that the aluminium plates do not touch each other.
1.4: Construct a stand for the capacitor using recycled materials. The stand should hold the capacitor securely and allow for easy connection of wires.
2. Experiment and Measurement
2.1: Connect the capacitor to the power supply using wires. Ensure that each plate of the capacitor is connected to one terminal of the power supply.
2.2: Using the multimeter, measure the voltage (V) across the capacitor and record the value.
2.3: Disconnect the capacitor from the power supply. Using the multimeter, quickly measure the voltage across the capacitor over time. Record these values.
3. Analysis and Discussion
3.1: Using your measurements, calculate the capacitance of the capacitor using the formula C = Q/V. Record this value in your report.
3.2: Discuss the charge stored on the capacitor and how it varies with voltage and time.
3.3: Discuss the concept of sustainability, and how you implemented it in the construction of your capacitor stand.
Project Submission
Following completion of the experiment, students should produce a report covering the following sections:
Introduction: Set the context for the project, explaining the relevance of the topic and outlining the aims of the project.
Method: Describe the theoretical concepts involved, the materials used, the step-by-step method for the experiment, and the measurements taken. Discuss and analyse the results obtained, linking them back to the theory.
Conclusion: Summarise the project, restating the key points, explaining what was learnt, and drawing conclusions about the project.
Bibliography: List the sources that you used to research your project.
This project should take each student approximately 12 hours to complete, including group discussions, building the capacitor, conducting the experiment, analysing the results and writing the report.
