# Current & Voltage Rules

### Overview

This lesson considers what we mean by current and voltage. Kirchhoff's current law is used to explain what happens to current in series and parallel circuits. Kirchhoff's voltage law is used to explain what happens to voltage in series and parallel circuits and highlight the difference between EMF and Potential Difference. Analogies are used to develop a more intuitive understanding of current and voltage and Kirchhoff's laws. The second part of the lesson looks at how to solve numerical problems involving current and voltage in simple circuits.

### Learning Objectives

• Apply current rules in series and parallel circuits
• Apply voltage rules in series and parallel circuits
• Calculate unknown values of voltage and current in circuits containing multiple components in series and/or parallel

### Lesson Content

Reading: Read the two sections about current. The first section explains what current is physically and gives us the equation relating charge and current. The second section considers what happens to current in a series circuit and at a junction in a parallel circuit. Building on last lesson, the prefixes used with large and small currents are reviewed. Make careful notes before moving on.

Reading: Read the two sections about voltage and the summary. The first section explains the physical meaning of voltage and introduces the terms EMF and Potential Difference. The equations for voltage are introduced. The second section considers Kirchhoff's voltage laws for series and parallel circuits. The prefixes used are reviewed and Kirchoff's Laws are summarised. Make careful notes before moving on.

Video (21 min): Watch the video about different analogies used to help develop a more intuitive understanding of current, voltage, charge and resistance. A note about the video: It took several goes to get the explanations right and even now I am not totally happy with all of it. The message here is treat analogies with a pinch of salt and don't read too much into them - they make an excellent discussion point. The water circuit starts at 0:16, the second water analogy at 4:03, the coal trucks at 8:49 and the student analogy at 15:53.

Reading: Having watched the video about different analogies, read about each analogy again and consider how each analogy helps us understand electrical circuits.

Reading: Read the first two sections of the webpage about simple circuit calculations. These two sections are the introduction and the current law. This is revision of the reading covered earlier about current.

Reading: Read the two sections about the voltage law. These sections are partly revision of the voltage laws introduced earlier but cover the application of the voltage laws in more detail. Make careful notes about each of the "routes" around a circuit.

Video (10 min): Watch the explanation of how to calculate current and voltage values in a simple circuit.

Reading: Work through the examples, on the webpage, of different simple circuit calculations. Use the answers to check your understanding. Consolidate any misunderstanding using the video and the previous sections of the webpage.

Exercise: Complete the exercises using the current and voltage laws. Use the answers to check your understanding.

### Lesson Review

Review your learning by working through the presentations or notes which summarise the website content.

Notes: PDF download. The website content in note form as a PDF document.

Presentation: Powerpoint download. Series and Parallel simple circuits analysed in terms of current and voltage using Kirchhoff's laws.

Notes: PDF download. Simple circuits and Kirchhoff's laws in note form as a PDF document.

### Self Assessment

Complete either the questions (pdf download) OR the on-line quiz. They are the same questions.

Quiz: On-line quiz questions. Questions about current and voltage in simple circuits. The diagrams are drawn slightly differently but the current and voltage laws apply in the same way.

Questions: PDF download. The same questions as the on-line quiz but as a PDF document with slightly different formatting.

### Self Evaluation

I can:

• Appreciate how current behaves in a series circuit
• Appreciate that current splits at a junction and how current behaves in a parallel circuit
• Apply the voltage laws for EMF and Pd to a series circuit
• Understand how the voltage laws apply to a parallel circuits
• Realise that the voltages across any parallel components must be the same
• Calculate current in each part of a simple circuit
• Calculate the EMF or Pd across each component in a simple circuit