Electricity
- Electricity is a form of energy that is used in electrical appliances such as computers, radios and electric fans.
- Electricity is a useful form of energy because it can be changed into many other forms.
- Sources of electricity for use in everyday life are
- Electric cells
- Small amounts of electrical energy are produced through chemical reactions.
- (Examples of electric cells are dry cells and accumulators.
- (They are used in many portable devices.
- Generators
- They convert mechanical energy into electrical energy.
- (Power stations use generators that are usually run by water, steam or gas.
- Solar cells that convert light energy from the sun into electrical energy.
Current
- Electric charges are made up of
- positive charges such as protons and positive ions.
- negative charges such as electrons and negative ions.
- When these electric charges flow, they produce current.
- Current is the rate of flow of electric charges.
- Figure 24.5 and Figure 24.6 below show the movement of free electrons in a conductor and the flow of electrons through a conductor, forming electricity.
- In an electric circuit, the direction of electric current is from the positive terminal to the negative terminal of a battery.
- However, electrons flow in the opposite direction, that is, from the negative terminal to the positive terminal of the battery.
Van de Graaff Generator
- The flow of electric current can be shown using a device known as the Van de Graaff generator.
- This device is a high voltage electrostatic generator which is able to produce a potential difference of millions of volts.
- It is used to create static electricity used for experimentation.
- It is made up of
- a motor
- two rollers
- a belt
- two brush assemblies and an output terminal (usually a metal or aluminum sphere).
Voltage
- Energy is needed to move electric charges through a conductor, in order to produce electricity.
- Voltage is the electrical force needed to move electric charges from one point to another in a conductor.
Resistance
- Resistance is the measure of how much an electrical component restricts current flow.
- A good conductor of electricity has a lower resistance and allows a larger electric current to flow through it.
- For example, copper is used in connecting wires as it has low resistance.
- Tungsten, on the other hand, has higher resistance. Some of the electrical energy that flows through it is transformed into light and heat.
- This energy loss slows down the movement of electric charges and reduces current flow.
