Science: Grade 6
Energy and Change: Electrical Circuits
ELECTRICAL CIRCUITS Electricity is the flow of electrical power or charge. There is a positi...
ELECTRICAL CIRCUITS Electricity is the flow of electrical power or charge. There is a positive and negative charge in all matter.
Electrical Energy
Lightning – Electrical Charge
An electrical current is the flow of charges that carry energy through a circuit. It is the movement of electrical charge. The electrical current provides energy for lighting, movement and heating.
Energy for Lighting
Energy for Heating
For electricity to flow it needs a continuous path and this path is called an electrical circuit. An electrical circuit is a loop or circle that electricity can travel around. The word “circuit” comes from the Latin word circuitus which means “go around”. Electricity can only flow in the circuit when the circuit has no breaks or gaps.
When you turn a switch on or off, you are closing or opening the circuit. The circuit must be closed for the electrical current to travel, i.e. the light switch must be on.
Closed Circuit – Switch is On Open Circuit – Switch is Off
For example, in a torch, the electricity flows from one end of the battery to the next, through the bulb and then back again into the battery. When the torch is switched off, the electricity stops flowing as the switch breaks the flow of the current.
The illustration below shows a circuit diagram of the torch.
In order for an electrical current to flow, three important conditions must exist: 1. There must be material in the circuit, such as a wire or cable that conducts electricity. 2. There must be a power source that pushes the power through the circuit.
Cables Conducting Electricity
Power Source
3. The circuit must be closed, so that there is direct uninterrupted flow of electricity from the power source and around the circuit.
Therefore an electrical circuit can be seen as a system as it has different parts that make the circuit work. The electricity flows from one part of the system to another through wires and other objects. A cell is a source of power that can produce electricity. It has a positive (+) terminal or pole and a negative (-) terminal or pole. Two or more cells connected together are called a battery. The cell or battery is known as the input device and the bulb or lamp in a circuit is known as the output device. The switch is known as the control or process device. Input
Electrical Symbols In an electrical circuit there are various electrical components. Symbols are used for each electrical component to draw diagrams of electrical circuits, so that they are always drawn in the same way. The main symbols used are shown in the table below. However, please note that some symbols may be drawn slightly differently in different parts of the world.
A circuit always needs a power source. In the example above the power source is a two cell battery. The circuit also has other electrical components, such as a bulb, wires and a switch. The wires are connected to the positive and negative terminals of the battery. The electrical current flows from the positive terminal of the battery around the circuit and back to the negative terminal. A Closed Circuit For the circuit to be completed and the bulb to light, the switch must be closed, as shown in the diagram below:
