Essential Concepts of Electricity and Magnetism

Electrical Fundamentals and Magnitudes

Key Electrical Magnitudes

• Voltage (V) / Potential Difference: Indicates the energy difference between two points in a circuit.
• Resistance (R): Indicates the opposition of a material to the passage of electric charge.
• Intensity (I) / Electric Current: Expresses the amount of electric charge that flows through a section of the circuit per second.
• Electrical Energy: Calculated as the product of the voltage supplied to the receiver, the intensity of the electric current flowing through it, and the time it is operating (E = V × I × t).
• Electric Power (P): Expresses the energy consumed by the receiver every second (P = V × I).

Direct Current (DC) vs. Alternating Current (AC)

Direct Current (DC)

DC flows consistently in one direction (conventionally, from positive to negative). The DC voltage and current intensity are constant.

Alternating Current (AC)

In AC, electrons change their direction of movement a constant number of times each second. The frequency of the alternating current depends on the speed of the alternators. The voltage and current sinusoidally fluctuate. Alternating voltage can reach hundreds of volts, and the current value can be several amperes.

Measuring Electrical Quantities

Essential Measuring Instruments

• Ammeter: Used to measure the intensity of current passing through any point of the circuit.
• Voltmeter: Used to measure the value of the potential difference (voltage) between two points on a circuit.
• Ohmmeter: Measures the value of electrical resistance in Ohms (Ω).
• Wattmeter: Used to measure the electrical power consumed by an appliance or machine.

The multimeter is capable of measuring different electrical quantities.

Using a Multimeter

Measuring Current Intensity (Amperes)

1. Connect the red probe to the 'A' terminal and the black probe to the 'COM' terminal.
2. Set the selector to the 'A' position.
3. The multimeter must be inserted in series with the circuit component.

Measuring Voltage (Volts)

1. Connect the red probe to the 'V' terminal and the black probe to the 'COM' terminal.
2. Set the selector to the 'V' position.
3. Connect the multimeter in parallel across the component.

Measuring Resistance (Ohms)

1. Connect the red probe to the 'V' or 'Ω' terminal and the black probe to the 'COM' terminal.
2. Set the selector to the position marked with Ω (Ohms).
3. Connect the tips at the ends of the element being measured.

Magnetism and Electromagnetism

Types of Magnets

• Natural Magnets: Materials, such as lodestone (iron ore), that are naturally magnetic.
• Artificial Magnets: Materials that acquire magnetic properties through various procedures.

The Magnetic Effect of Electric Current

An electromagnet is a temporary artificial magnet created by applying an electric current to a conductor. The greater the intensity of current flowing through the conductor, the greater the magnetic effect produced. An electromagnet typically consists of a conductor coiled around a soft iron bar.

Electric Machines

Electric Generators (Dynamo and Alternator)

• Dynamo: A DC generator.
• Alternator: An AC generator.

How the Electric Motor Works

A simple motor consists of:

• Rotor: The mobile assembly, consisting of one or more copper coils wrapped around an iron core. This assembly is mounted on the motor's axis of rotation.
• Collector (Commutator): A set of semi-cylindrical segments that reverses the current direction.
• Stator: The fixed assembly located around the rotor. It consists of a fixed magnet attached to the housing. Contacts with the collector, called brushes, connect the motor to a power source (battery).

The rotor is positioned on the axis of rotation between the magnet poles. When connected to a battery, the coil acts as an electromagnet. Poles of the same polarity on the electromagnet and the fixed magnet repel, while opposite poles attract. This force causes the coil to rotate until the poles of different polarities are aligned, continuing the rotation cycle.