My Pals are Here! Science © 2008 Marshall Cavendish (Singapore) Private Limited © 2009 Marshall Cavendish International (Singapore) Private Limited

Questions to think about… What are the components in an electric circuit? How can these components be represented in a circuit diagram? What are closed and open circuits? © 2009 Marshall Cavendish International (Singapore) Private Limited

The uses of electricity Many things around us need electricity to work. Like heat and light, electricity is a form of energy. Without electricity, these equipment cannot work. Equipment that use electricity are fitted with electrical systems. vacuum cleaner calculator computer © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Components of a simple electric circuit o An electrical system can consist of one or more electric circuits. o These circuits are connected together in order for the system to function. o Electric circuits can be simple or complex. a simple electric circuit © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Components of a simple electric circuit o What are the components of a simple electric circuit? switch battery wire bulb © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Battery – an energy source o In the electric circuit below, the battery provides energy to light up the bulb. o Hence, the battery is the source of energy. © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Battery – an energy source o Without a battery, the bulb does not light up. © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Battery – an energy source o A battery has two poles – a positive pole and a negative pole. o Inside a battery, there are chemicals. o These chemicals produce electricity when the two poles of a battery are connected. positive pole negative pole car battery small batteries © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Wires o In an electric circuit, electricity flows through wires. o Wires are usually made of copper. o When a wire is connected to a source of energy, like a battery, a current flows through the circuit. o It is called an electric current. copper wires © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Switch o A switch controls the flow of the electric current in a circuit. o A circuit can have one or more switches. a light switch © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Bulb o A bulb converts electrical energy to light and heat energy. o A bulb has these parts: filament The filament is usually made of a metal called tungsten. When a current flows through the filament, the filament glows and gives off light and heat. glass bulb The filament is enclosed in a glass bulb. There is very little air inside the bulb, so that the filament does not burn up. The glass bulb also prevents the filament from being damaged. metal casing & metal tip The metal casing and metal tip are the parts of the bulb which are connected to an electrical circuit. metal casing metal tip © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Bulb o In order for a bulb to light up, we need to connect the battery to both the metal casing and metal tip of the bulb. © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Bulb o When only the metal casing or the metal tip is connected to the battery, the bulb will not light up. © 2009 Marshall Cavendish International (Singapore) Private Limited

Electric circuits Bulb o When too much current flows through a bulb, the filament gets very hot and melts. o We then say that the bulb has blown and it can no longer light up again. broken filament © 2009 Marshall Cavendish International (Singapore) Private Limited

Circuit diagram We use a circuit diagram to represent an actual circuit. A circuit diagram shows how the components of a circuit are connected to one another. Different components of a circuit are represented by different symbols. © 2009 Marshall Cavendish International (Singapore) Private Limited

Symbols in an electric circuit Component of an actual circuit battery bulb switch2 batteries wire Symbol used in circuit diagrams © 2009 Marshall Cavendish International (Singapore) Private Limited

Circuit diagram Actual circuitCircuit diagram © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits An electric current only flows in a wire if the circuit is complete. This means that the components in a circuit must be properly connected, so that the current can flow through all these components. A circuit that allows a current to flow through it is called a closed circuit. © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits A closed circuit © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits When the components of a circuit are not properly connected, electric current does not flow. This means that there is a break in the circuit. This kind of circuit is called an open circuit. © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits An open circuit a break in the circuit © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits A switch controls whether the circuit is complete or not. When a switch is open, there is a break in the circuit and the current does not flow through the circuit. Thus, a switch can be used to open or close a circuit. © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits switch is open bulb does not light up © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits switch is closed bulb lights up © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits Switches S1 and S2 are closed. Current flows through switches S1 and S2. Thus, both light bulbs B1 and B2 light up. S1 S2 B1 B2 © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits Switch S1 is open while switch S2 is closed. Current flows through switch S2 only. Thus, only bulb B2 lights up. S1 S2 B1 B2 © 2009 Marshall Cavendish International (Singapore) Private Limited

Closed and open circuits Switch S1 is closed, while switch S2 is open. Current does not flow through the circuit. Thus, both light bulbs do not light up. S1 S2 B1 B2 © 2009 Marshall Cavendish International (Singapore) Private Limited

My Pals are Here! Science © 2008 Marshall Cavendish (Singapore) Private Limited © 2009 Marshall Cavendish International (Singapore) Private Limited