Electromagnetic Waves

ELECTROMAGNETIC WAVES

INTRODUCTION

We see the world around us through light. Light from the Sun is one of the sources of energy without which we human beings cannot survive in this planet. Light plays crucial role in understanding the structure and properties of various things from atom to universe. Without light, even our eyes cannot see objects. What is light?. This puzzle made many physicists sleepless until middle of 19th century. Earlier, many scientists thought that optics and electromagnetism are two different branches of physics. But from the work of James Clerk Maxwell, who actually enlightened the concept of light from his theoretical prediction is that light is an electromagnetic wave which moves with the speed equal to 3 × 10⁸ m/s (in free space or vacuum). Later, it was confirmed that light is just only small portion of electromagnetic spectrum, which ranges from gamma rays to radio waves.

In the unit 4, we studied that time varying magnetic field produces an electric field (Faraday’s law of electromagnetic induction). Maxwell strongly believed that nature must possess symmetry and he asked the following question, “when the time varying magnetic field produces an electric field, why not the time varying electric field produce a magnetic field?”

Later he proved that indeed it exists, which is often known as Maxwell’s law of induction. In 1888, H. Hertz experimentally verified Maxwell’s predication and hence, this understanding resulted in new technological invention, especially in wireless communication, LASER (Light Amplification by Stimulated Emission of Radiation) technology, RADAR (Radio Detection And Ranging), etc.

In today's digital world, cell phones (Figure 5.2 (a)) have greater influence in our day to day life. It is a faster and more effective mode of transferring information from one place to another. It works on the basis that light is an electromagnetic wave. In hospitals, the location of bone fracture can be detected using X-rays as shown in Figure 5.2 (b), which is also an electromagnetic wave. For cooking microwave oven is used. The microwave is also an electromagnetic wave. There are plenty of applications of electromagnetic waves in engineering, medical (example LASER surgery, etc), defence (example, RADAR signals) and also in fundamental scientific research. In this unit, basics of electromagnetic waves are covered.