## Electromagnetic Waves

• INTRODUCTION
• Maxwell formulated a set of equations involving electric and magnetic fields, and their
sources, the charge and current densities. These equations are known as Maxwell's
equations. Together with the Lorentz force formula, they mathematically express all the
basic laws of electromagnetism

• DISPLACEMENT CURRENT
• We have seen that an electrical current produces a magnetic field around it. Maxwell showed that for logical
consistency, a changing electric field must also produce a magnetic field. This effect is of great importance
because it explains the existence of radio waves, gamma rays and visible light, as well as all other forms of
electromagnetic waves

• DISPLACEMENT CURRENT
• We have seen that an electrical current produces a magnetic field around it. Maxwell showed that for logical
consistency, a changing electric field must also produce a magnetic field. This effect is of great importance
because it explains the existence of radio waves, gamma rays and visible light, as well as all other forms of
electromagnetic waves.

• DISPLACEMENT CURRENT
• We have seen that an electrical current produces a magnetic field around it. Maxwell showed that for logical
consistency, a changing electric field must also produce a magnetic field. This effect is of great importance
because it explains the existence of radio waves, gamma rays and visible light, as well as all other forms of
electromagnetic waves.

• ELECTROMAGNETIC WAVES
• How are electromagnetic waves produced ? Neither stationary charges Nor charges in uniform motion
(steady currents) can be sources of electromagnetic waves. The former produces only electrostatic
field, while the latter produces magnetic fields that, however, do not vary with time. It is an
important result of Maxwell's theory that accelerated charges radiate electromagnetic waves.

• Nature of electromagnetic wave
• It can be shown from Maxwell's equations that electric and magnetic field in an electromagnetic wave are perpendicular
to each other and to the direction of propagation. It appears reasonable, say from our discussion of the displacement
current. Consider Fig 2. The electric field inside the plates of the capacitor is directed perpendicular to the plates.
The magnetic field this gives rise to via the displacement current is along the perimeter of a circle parallel to the
capacitor plates. So B and E are perpendicular in this case. This is a general feature

• ELECTROMAGNETIC SPECTRUM
• At the time Maxwell predicted the existence of electromagnetic waves, the only familiar electromagnetic
waves were the visible light waves. The existence of ultraviolet and infrared waves was barely established.

• Radio waves are produced by the accelerated motion of charges in conducting
wires

• Microwaves
• Microwaves (short-wavelength radio waves), with frequencies in the gigahertz (GHz) range,
are produced by special vacuum tubes (called klystrons, magnetrons and Gunn diodes).

• Infrared waves
• Infrared waves are produced by hot bodies and molecules. This band lies adjacent to the
low-frequency or long-wave length end of the visible spectrum. Infrared waves are sometimes
referred to as heat waves. This is because water molecules present in most materials

• Visible rays
• It is the most familiar form of electromagnetic waves. It is the part of the spectrum that
is detected by the human eye.

• Ultraviolet rays
• It covers wavelengths ranging from about 4 Ã— 10â€“7 m (400 nm) down to 6 Ã— 10â€“10 m (0.6 nm).
Ultraviolet (UV) radiation is produced by special lamps and very hot bodies. The sun is an
important source of ultraviolet light. But fortunately

• X-rays
• Beyond the UV region of the electromagnetic spectrum lies the X-ray region. We are
familiar with X-rays because of its medical applications.

• Gamma rays
• They lie in the upper frequency range of the electromagnetic spectrum and have wavelength of from about

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