Understanding Basic Electricity: Voltage, Current & Circuits
Basic Electrical Concepts
Voltage
The energy provided by a source (like a generator) to push electrons through a circuit is called voltage.
Electric Current
Electric current (intensity) is the rate at which electrical charges flow through a circuit per unit time.
Resistance
Resistance measures how difficult it is for electric current to pass through a material. Its unit is the ohm (Ω).
Electrical Power
Power is a key characteristic of an electrical device (recipient). It indicates the capacity of a machine to perform its function, essentially how quickly it uses energy. It is measured in watts (W). The formula is: P = V * I (Power = Voltage * Current).
Ohm’s Law
Ohm’s Law states that the electric current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points and inversely proportional to the resistance (R) between them. The formula is: I = V / R.
Circuit Connections
Series Circuits
When different elements in a circuit are connected one after another, so the same electrical current flows through each element, they are said to be connected in series.
Parallel Circuits
When elements in a circuit are connected such that the current divides at a connection point, flows through the elements separately, and then rejoins, these elements are connected in parallel.
Mixed Circuits
A circuit containing both series and parallel connections is called a mixed circuit. For example, two lamps connected in parallel might be connected in series with another component.
Electrical Measurement Tools
Voltmeter
A voltmeter is used to measure voltage (tension). It has two terminals, often with probes or clips, which are connected in parallel across the two points in the circuit where the voltage difference is to be measured.
Ammeter
An ammeter measures the current (intensity) flowing through a circuit. It must be connected in series with the component whose current is being measured, meaning the circuit must be broken to insert the ammeter.
Ohmmeter
An ohmmeter is used specifically to measure the electrical resistance of a component (like a resistor) or a part of a circuit. The component must be disconnected from the power source before measuring.
Multimeter
Technicians often use a multimeter (or tester) to measure voltage, current, and resistance. Multimeters typically have different settings (scales) for each quantity. When used as a voltmeter, it’s connected in parallel. When used as an ammeter, it’s connected in series.
Effects of Electric Current
We cannot directly see electric current flowing in a circuit, but we can detect its presence through its effects:
- Thermal Effects: Current flowing through a resistance generates heat (Joule effect). Examples include stoves, toasters, and electric heaters.
- Magnetic Effects: Current creates magnetic fields.
- Light Effects: Current can produce light (e.g., in lamps).
- Acoustic Effects: Current can produce sound (e.g., in speakers).
- Dynamic Effects: Current can cause motion (e.g., in motors).
Electrical Safety and Protection
Circuit Protection: Fuses and Breakers
Excessive heat from high current can be dangerous. Protection devices are used:
- Fuses: These contain a wire made of a material with a low melting point. If the current exceeds a safe level, the wire melts, breaking the circuit. Fuses are placed at the beginning of installations and rated for specific currents.
- Circuit Breakers: These are automatic switches that interrupt the circuit when excessive current (due to overload or short circuit) is detected. They can often be reset.
Short Circuits
A short circuit is a dangerous situation where current flows directly between the poles of the source (e.g., generator) without passing through a load (receptor), causing a very high current and significant heat generation.
Electromagnetism Fundamentals
Electromagnetism is the branch of physics studying the relationship between electricity and magnetism. A fundamental principle is that every conductor carrying an electric current creates a magnetic field around it.
Electromagnets
An electromagnet is a temporary magnet created when electric current flows through a coil of wire (often copper) wound around a core material (typically iron). It acts as a magnet only while the current is flowing.
Electromagnetic Generators
An electromagnetic generator is a device that converts mechanical energy (motion) into electrical energy.
Electromagnetic Induction
Electromagnetic induction is the phenomenon where a voltage (and thus potentially a current) is produced in a conductor (like a coil of wire) when it is exposed to a changing magnetic field (e.g., by moving a magnet near the coil or moving the coil near a magnet).
Electric Motors
An electric motor is a machine that transforms electrical energy into mechanical energy (motion or force).