4.1. INTRODUCTION

Both Electricity and Magnetism have been known for more than 2000 years. However, it was only about 200 years ago, in 1820, that it was realised that they were intimately related.

For many centuries, electricity and magnetism were studied separately without a clear understanding of their connection. It wasn't until 1820 that Danish physicist Hans Christian Oersted discovered how they relate to one another through his famous experiment, demonstrating that an electric current can influence a magnetic compass.

Imagine two friends who have been living in the same neighborhood for years but never interact. It takes a chance meeting for them to realize they have a lot in common. Similarly, electricity and magnetism were always present but only came together through Oersted's discovery.

During a lecture demonstration, Oersted noticed that a current in a straight wire caused a noticeable deflection in a nearby magnetic compass needle.

Oersted's experiment involved running an electric current through a wire and observing the effect it had on a nearby compass. He found that the compass needle, which normally points north, deflected when the current was flowing. This indicated that the current was generating a magnetic field around the wire, showing a direct interaction between electricity and magnetism.

Think of it like a car driving past a field. The wind created by the moving car can push grass in the field. In Oersted’s setup, the electric current is like the car, and the magnetic field it creates is like the wind that influences the compass needle.

He concluded that moving charges or currents produced a magnetic field in the surrounding space.

Oersted established that electric currents create magnetic fields, which can interact with magnetic objects like compass needles. The magnetic field lines around a current-carrying wire form concentric circles, showing how the field changes with distance from the wire. This discovery laid the groundwork for understanding electromagnetism.

Imagine dropping a pebble into a still pond. The ripples form circles that spread outward. In the same way, when current flows through a wire, the magnetic field spreads out in concentric circles around it, demonstrating how currents can affect their surroundings.

Following this, there was intense experimentation. In 1864, the laws obeyed by electricity and magnetism were unified and formulated by James Maxwell.

Oersted’s findings spurred further experiments and developments in the field. By 1864, James Clerk Maxwell formulated the equations that unified electricity and magnetism into one comprehensive theory: electromagnetism. This breakthrough not only advanced theoretical physics but also paved the way for technologies such as radio and light communications.

Consider how different ingredients combine to create a new dish. Just as Oersted and Maxwell combined findings from electricity and magnetism to create the theory of electromagnetism, chefs often combine various flavors to create a signature recipe that revolutionizes the culinary landscape.

In this chapter, we will see how magnetic field exerts forces on moving charged particles, like electrons, protons, and current-carrying wires.

This chapter will explore the effects of magnetic fields on charged particles and wires. We will learn about how moving charges produce magnetic fields and how these fields, in turn, exert forces on objects within them, covering principles like the operation of devices such as galvanometers and cyclotrons.

Think of it like a football game where players (charged particles) react to the movements of each other (magnetic fields). Just as players change their movements based on the arrangement of their teammates and opponents, charged particles respond dynamically to the magnetic fields around them.

We adopt the following convention: A current or a field (electric or magnetic) emerging out of the plane of the paper is depicted by a dot (•). A current or a field going into the plane of the paper is depicted by a cross (×).

In this chapter, we will use specific symbols to represent directions of currents and fields. A dot represents a current coming towards you from the page, while a cross indicates a current going away. This notation will help in visualizing and understanding the relationships between various components in our discussions.

Imagine using hand signals in a crowded area to communicate directions. A dot could symbolize a signal towards someone directly in front of you, while a cross would indicate a signal aimed at someone further away or behind. Just as those signals help convey information efficiently in person, these symbols will clarify concepts in electromagnetism.

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