Module 115. Electricity, Magnetism and Electronics

Electricity, magnetism, and electronics form the core of physical science and modern technology, collectively governing the flow of charge, the generation of magnetic fields, and the operation of electronic devices. Their interrelationship underpins everything from household appliances and communication systems to industrial automation and scientific instrumentation. The study of these phenomena has evolved from simple observations of static charge to sophisticated electronic systems that define the modern world.

Electricity

Electricity refers to the movement and interaction of electric charges, primarily electrons, within conductors. It can exist in two main forms — static electricity and current electricity.

• Static Electricity: Occurs when charges accumulate on an object’s surface due to friction or induction, as seen when rubbing a balloon on hair.
• Current Electricity: Involves the continuous flow of electric charge through a conductor, typically produced by a cell or battery.

The rate of charge flow is known as electric current (I), measured in amperes (A), and given by:
I=QtI = \frac{Q}{t}I=tQ​
where Q is the charge (in coulombs) and t is time (in seconds).
A potential difference (V), measured in volts (V), drives this current through a circuit. It represents the work done in moving a unit charge between two points:
V=WQV = \frac{W}{Q}V=QW​
The opposition offered by a material to current flow is known as resistance (R), measured in ohms (Ω). Ohm’s Law, formulated by Georg Simon Ohm, establishes the fundamental relationship:
V=IRV = IRV=IR
Electric power — the rate at which electrical energy is consumed or produced — is given by:
P=VIP = VIP=VI
The unit of electrical energy is the kilowatt-hour (kWh), commonly used in electricity billing.
Types of Current:

• Direct Current (DC): Flows in one direction, typically produced by batteries.
• Alternating Current (AC): Periodically changes direction, as in household mains supply (commonly 230 V, 50 Hz in the UK).

Electrical circuits consist of conductors, insulators, and components connected in series or parallel configurations. Devices such as resistors, capacitors, and diodes control the current and voltage distribution within circuits.

Magnetism

Magnetism is the physical phenomenon produced by moving electric charges or magnetic materials such as iron, cobalt, and nickel. It manifests as a magnetic field, a region around a magnet where magnetic forces are exerted.
Magnetic Poles: Every magnet has two poles — north (N) and south (S) — which always exist in pairs. Like poles repel, while unlike poles attract. The lines of magnetic force emerge from the north pole and enter the south pole, forming closed loops.
The relationship between electricity and magnetism was first discovered by Hans Christian Ørsted in 1820, who observed that an electric current deflected a nearby compass needle. This led to the development of electromagnetism.
Electromagnetism: When an electric current flows through a wire, it produces a magnetic field around it. The strength of this field increases with current and the number of turns in the wire coil. A soft iron core placed within the coil forms an electromagnet, which can be made stronger or weaker by adjusting the current.
Electromagnets have numerous applications, including electric bells, relays, cranes, and motors.
Magnetic Field of Earth: The Earth itself acts as a giant magnet, with magnetic poles near its geographic poles. This natural magnetic field protects the planet from solar radiation and enables compass navigation.

Relationship between Electricity and Magnetism

The close relationship between electricity and magnetism forms the basis of electromagnetic theory. The two fundamental principles governing this relationship are:

• Electromagnetic Induction: Discovered by Michael Faraday in 1831, it states that a changing magnetic field induces an electric current in a nearby conductor. This principle is utilised in electric generators and transformers.
• Electromagnetic Force: Explained by James Clerk Maxwell, uniting electricity and magnetism into a single framework known as electromagnetism, represented mathematically by Maxwell’s equations.

Applications:

• Electric Generators: Convert mechanical energy into electrical energy using electromagnetic induction.
• Electric Motors: Operate on the reverse principle, converting electrical energy into mechanical energy.
• Transformers: Transfer electrical energy between circuits by electromagnetic induction, adjusting voltage levels for efficient power transmission.

Electronics

Electronics is the branch of physics and engineering dealing with the control and manipulation of electrons using various devices and circuits. Unlike conventional electrical systems focused on power, electronics primarily concerns signal processing, communication, and computation.
Basic Electronic Components:

• Resistor: Controls current flow.
• Capacitor: Stores and releases electrical energy temporarily.
• Inductor: Stores energy in a magnetic field when current flows through it.
• Diode: Allows current to flow in only one direction; used for rectification.
• Transistor: Acts as a switch or amplifier; the fundamental building block of modern electronics.
• Integrated Circuit (IC): A miniaturised electronic circuit containing thousands of transistors and other components on a semiconductor chip.

Semiconductors: Semiconductors, such as silicon and germanium, are materials with conductivity between conductors and insulators. Their behaviour can be modified by adding impurities (doping), forming p-type and n-type materials. When combined, they form p–n junctions, the foundation of diodes, transistors, and modern electronic devices.
Analogue vs Digital Electronics:

• Analogue electronics deal with continuous signals (e.g., sound or light intensity).
• Digital electronics handle discrete binary signals (0 and 1), forming the basis of computers and digital communication.

Key Electronic Devices and Applications:

• Rectifiers: Convert AC to DC.
• Amplifiers: Increase the strength of signals.
• Oscillators: Generate repetitive waveforms.
• Logic Gates: Perform logical operations in computing systems.
• Microprocessors and Microcontrollers: Control and process data in computers, smartphones, and embedded systems.
• Sensors and Transducers: Convert physical quantities like temperature, pressure, or light into electrical signals.

Communication Systems: Electronics revolutionised communication through radio, television, mobile phones, and the internet. Modulation techniques (AM, FM, and digital modulation) enable transmission of information via electromagnetic waves.
Power Electronics: This subfield deals with the conversion and control of electrical energy using semiconductor devices. Applications include power supplies, inverters, and renewable energy systems such as solar inverters.

Interconnection of Electricity, Magnetism, and Electronics

These three domains are intrinsically linked through the behaviour of charge and energy transformation:

• Electric current produces magnetic fields, and changing magnetic fields generate electric currents.
• Electromagnetic waves, predicted by Maxwell, propagate through space as oscillating electric and magnetic fields — the foundation of radio, microwaves, and light.
• Electronic systems harness these principles to transmit, process, and store information.

Modern Applications and Impact

The principles of electricity, magnetism, and electronics permeate modern civilisation:

• Power generation and transmission rely on electromagnetic induction.
• Transportation systems, such as electric vehicles and magnetic levitation trains, use electromagnetic control.
• Medical technologies, including MRI scanners and defibrillators, employ electromagnetic principles.
• Computers and mobile devices depend entirely on semiconductor electronics.
• Space communication, robotics, and automation owe their existence to advanced electronics and electromagnetism.

Scientific and Technological Significance

From the discovery of electric charge to the invention of the transistor, the study of electricity and magnetism has shaped modern science and technology. Electronics continues to evolve rapidly with developments in nanotechnology, quantum computing, and artificial intelligence, expanding human capability and connectivity.