Introduction to Electric Circuits

1. Electric Circuits

An electric circuit is a route around which electrons circulate. It consists of a generator, a cable, a switch, and a receiver. Electric current is the flow of electrons around a circuit. We need a generator to maintain the current.

Types of Materials

• Conductors: Allow electric currents to pass through them (e.g., metals).
• Insulators: Don't allow electric current to pass through them (e.g., plastics).
• Semiconductors: Have properties between conductors and insulators (e.g., silicon and germanium).

Electrical Resistance

The electrical resistance of a material is a measure of the degree to which the material opposes an electric current flowing through it.

• Metals have hardly any electrical resistance; insulators have very high levels of resistance.
• Its value depends on the material used and its form.
• Resistance increases with the length of a cable and decreases with the thickness.

Components of a Circuit

• Generators: Provide the necessary energy for electrons.
• Control elements: Direct and interrupt electric current.
• Receivers: Transform electric energy into usable energy.
• Protection elements: Protect circuits and people.

2. Types of Current

1. Direct Current (DC): The electrons always flow in the same direction and with a steady current.
2. Alternating Current (AC): The positive and negative terminals are constantly changing; the electrons don't have the same level of current. We obtain this alternating current through generators in power stations. The equivalent value of an alternating electric current is the value that a direct current should have to produce the same energy effect. Transformers are used to increase or reduce the alternating voltage.

Electric Energy and Power

Electric energy is measured in joules (J) [E = V · I · t]. The electricity consumed can be transformed into different types of energy:

• Motors: Transform electric current into rotary movement.
• Light bulbs: Transform electric current into light.
• Radiators: Transform electric current into heat.

Electric power is the capacity of an electric receiver to transform energy in a fixed period of time. It is measured in watts (W).

3. Effects of Electric Currents

1. Heat: The movement of electrons in a cable causes continuous collisions and an increase in the temperature of the cable.
2. Light: There are two ways to produce light:
   • Incandescent light bulbs: Produce light through incandescence.
   • Fluorescent tubes: The interior of the glass is lined with a layer of phosphorescent material.
   • Low energy bulbs: Consume much less electric energy.
3. Electromagnetism: All electric currents create magnetic fields. A changing magnetic field can produce an electric current. An electromagnetic mechanism is any appliance that can use electromagnetic effects to produce electricity or convert it into mechanical energy.
4. Electronic Components:
   • Fixed resistors: Impede the flow of electric currents.
   • Variable resistors: Potentiometers, thermistors, and light-dependent resistors.
   • Capacitors: Can store electric charge.
   • Diodes: Are made of semiconductor materials and only allow current to flow in one direction.
   • Transistors: Have three leads: emitter, base, and collector.

Key Words

• Light bulb: Hollow glass object, fitted to a lamp, which provides light.
• Domestic appliance: An electric appliance that we use at home, such as a fridge.
• Flow: The continuous movement of something in a given direction.
• Conventional symbol: A simple but carefully defined picture used to represent a component.
• Sum: The total of two or more values when they are added together.
• Branch: The separate parts of a circuit that the electric current flows through.
• Socket: Hole or group of holes which receive a plug or lead to connect an appliance to an electric circuit.
• Coil: Length of insulated wire wrapped around a core.
• Collision: When two or more objects hit each other.
• Magnetic field: An area around a magnet where the forces of magnetism act.
• Lead: A small wire used to make connections.