A neutral atom has the same number of protons as electrons. Eg. A neutral oxygen atom has 8 protons and 8 electrons.
Electrons can be removed from an atom, resulting in a positively charged atom. - - + + Neutral Positive
Electrons can also be added to an atom, resulting in a negatively charged atom. - - + Neutral Negative -
An atom with an uneven number of protons and electrons is called an ion. Electrons can be separate from atoms and can move freely within and between certain substances. This is why metals conduct electricity.
Electricity is a convenient type of energy that travels very fast and can be transformed into a variety of other types of energy.
There are two types of electricity. Static Electricity Current Electricity
Static E occurs within insulators. When the insulator is rubbed electrons are either added or removed, and the object is charged. + -
When a plastic rod is rubbed with a wool cloth, the rod will lose electrons to the cloth and become positively charged. The wool becomes negatively charged. + + + + + + - - - - - -
Static electricity is caused by a surplus or deficiency of electrons in an object. The object holds stored electrical energy. - - - - - -
If two objects have opposite charges they will attract each other. If they have the same charges they will repel. +- --
Electrical currents happen when free electrons travel from an area which is negatively charged to an area which is positively charged. Electricity needs a continuous pathway (circuit) in order to flow.
A substance like copper has free electrons and is an electrical conductor. Plastic is said to be an electrical insulator because it does not have free electrons.
ComponentSymbol Wire Single Cell Battery of Cells Open Switch Closed Switch Lamp Fuse
A circuit consists of at least 3 main parts: 1. An energy source (e.g.. battery). 2. An energy user (e.g.. light bulb). 3. A complete conducting pathway (wires)
Draw a simple circuit showing one light bulb controlled by a switch and powered by 2 cells.
When electrons flow around a circuit they create current. We can measure the amount of electrons flowing in a circuit with an ammeter. The symbol for current is I, because it describes the intensity of the current.
The ammeter measures in units called amperes (or amps) and is represented by the symbol A. In circuit diagrams we represent an ammeter by the symbol: A
An ammeter must be connected in series at the point where you wish to measure the current. A
There are 2 types of current: Direct Current (DC) – Electrons flow in only one direction. (E.g. Battery powered devices) Alternating Current (AC) – Direction changes 50 times a second. (E.g. Electricity from mains)
Current in a circuit carries electrical energy. Electrons gain energy from the energy source and lose energy from the energy users, where it is converted into other forms.
Voltage gain – the increase in electrical energy. Voltage loss – the decrease in electrical energy. We represent the gain or loss in voltage by the symbol V.
The unit for voltage is the volt and can be measured with a voltmeter. In circuit diagrams we represent an voltmeter by the symbol: V
A voltmeter can only measure the change in voltage so it must be connected in parallel around a lamp or battery. V
The amount of voltage lost at an energy user is equal to the amount of voltage gained from the batteries. In a series circuit the voltage loss is shared between components. In parallel the voltage loss is the same in both components.
Conductors are materials that allow the flow of electric charge. Metals are good conductors. Insulators are materials that do not allow the flow of electric charge. Plastic is an example of a good insulator.
It is the delocalized electrons involved in metallic bonding that allow metals to conduct electricity. The delocalized electrons are free to flow through the metal and so carry a current. Insulating materials do not contain free electrons and so current is unable to flow.