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ScienceOnline is an interactive resource for students and teachers of science.

The site provides access to a range of activities related to the New Zealand science curriculum for Years 9-11. Both Astronomy and Earth Science have been included as well as the core science areas of Physics, Chemistry and Biology. There are interactive notes and diagrams, self-marking tests, and useful links to other science websites. The site is completely up to date with NCEA requirements at Year 11 with details of achievement standards linked to topics in each of the five subject areas.

ScienceOnline has been developed by Peter Biggs, former science teacher and author of the Blue Science Book, and Sandy McGivern, science teacher, who manages the site.

In this document:

• Introduction
• Short circuit
• A simple circuit
• Another simple circuit
• Tracing the current path in the lab
• Take the test for this topic
• Take the test for this topic

Introduction

An electric circuit provides a complete path for the charges (the current) to move from one terminal (called positive +) to the other terminal (negative -).

Short circuit

The current must always pass through an electrical component. If this component is bypassed the circuit is said to be short-circuited and damage will occur to the wires or the power supply.

Every circuit you make must be checked to avoid such a short circuit. This can be done by using your finger to trace the path of the current from the positive terminal of the power supply back to the negative terminal.

A simple circuit

A simple circuit can be drawn incorporating two light bulbs and a switch.

Press the red button to complete the curcuit

Another simple circuit

In the following circuit, the three switches S₁, S₂ and S₃ have an effect on the circuit in different ways.

Tracing the path of the current on the circuit diaram will show the following:

• Closing switch S₁ only will leave both lamps unlit because the circuit is not complete.
• To complete the circuit, both switch S₁ and either (or both) switches S₂ and S₃ need to be closed.
• Closing switches S₁ and S₂ will make only lamp A light up.
• Closing switches S₁ and S₃ will make only lamp B light up.
• Closing switches S₁, S₂ and S₃ will make both lamps A and B light up.

Test this out for yourself. Click on a switch to turn it on or off.

Tracing the current path in the lab

When you construct circuits in the lab it is not always obvious how the current flows by looking at the mixture of wires and lamps. The only way to see exactly what is happening is to trace (using your finger) the path of the current from one terminal of the battery or power pack through the connections to the other battery terminal.