Electromagnetic Waves Class 12 Physics Chapter 8 One Shot | New NCERT CBSE

Introduction to Electromagnetic Waves

• Visible light enables us to see our surroundings.

• X-rays and laser eye surgery are applications of electromagnetic waves.

• Microwaves are used for cooking.

• Electromagnetic waves have a wide range of applications.

What are Electromagnetic Waves?

• Definition: Electromagnetic waves are coupled time-varying electric and magnetic fields that propagate through space.

• "Coupled" indicates a connection between the time-varying electric field and magnetic field.

• Both fields change over time and are interconnected, which results in the propagation of the wave.

Mathematical Basis of Electromagnetic Waves

• Maxwell's equations explain the behavior of electromagnetic waves.

• These equations describe how electric fields relate to magnetic fields and vice versa.

Maxwell's Proposal

• Maxwell proposed a theory similar to Faraday's Law; the idea that a changing electric field can generate a magnetic field.

• Emphasizes the interconnection between electric and magnetic fields and their dependence on time.

Faraday’s Law

• States that a changing magnetic field induces an electric field.

• Example: Moving a magnet near a coil generates an induced electric current.

• Induced EMF from changing magnetic flux affects current and electric field.

Exploring Maxwell's Theory

• Maxwell questioned if a time-varying electric field could also generate a magnetic field, leading to deductions regarding Ampère's Law.

• Identified inconsistencies in Ampère's circuital law, noting that it is not universally valid.

Electromagnetic Waves in Technology

• Infrared waves are used in devices like TV remotes, facilitating remote communication.

• Visible light (light waves) permits us to see, operating within a frequency range of 4 x 10^14 Hz to 7 x 10^14 Hz.

• The spectrum of visible light includes violet, indigo, blue, green hues, etc.

Ultraviolet Radiation

• UV rays, which are part of solar radiation, can be harmful, causing skin diseases and cancers.

• An essential source of Vitamin D is obtained from sunlight, although excessive exposure increases risks, especially due to ozone depletion.

Ozone Layer and UV Radiation

• The ozone layer protects against UV radiation but has developed holes due to harmful substances like chlorofluorocarbons (CFCs).

• The depletion of this layer leads to increased transmission of UV rays to the Earth.

Benefits of UV Waves

• Despite their risks, UV rays have applications, such as in LASIK eye surgery, demonstrating their beneficial properties.