Electromagnetic Waves – JEE Mains Physics
1. Displacement Current
- Displacement current is a concept introduced by Maxwell to account for the changing electric field in a capacitor. It is defined as:
I_d = ε₀ (dΦ_E / dt)
where I_d is the displacement current, ε₀ is the permittivity of free space, and dΦ_E / dt is the rate of change of the electric flux. - Displacement current is essential for the continuity of current in an electric circuit, especially in capacitive circuits.
2. Electromagnetic Waves and Their Characteristics
- Electromagnetic waves are transverse waves that propagate through space carrying both electric and magnetic fields. These waves do not require a medium and can travel through a vacuum.
- The speed of electromagnetic waves in a vacuum is the speed of light (c), given by:
c = 1 / √(ε₀μ₀)
where ε₀ is the permittivity of free space and μ₀ is the permeability of free space. - Electromagnetic waves exhibit properties such as reflection, refraction, diffraction, and polarization.
3. Transverse Nature of Electromagnetic Waves
- Electromagnetic waves are transverse in nature, meaning that the oscillations of both the electric and magnetic fields are perpendicular to the direction of wave propagation.
- In an electromagnetic wave, the electric field (E) oscillates in one plane, and the magnetic field (B) oscillates in a plane perpendicular to it. Both fields are perpendicular to the direction of propagation.
4. Electromagnetic Spectrum
- The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. It is divided into different regions based on frequency and wavelength:
- Radio Waves: These waves have the longest wavelength and are used for communication.
- Microwaves: Used for cooking and communication, they have shorter wavelengths than radio waves.
- Infrared: Invisible to the human eye, infrared waves are used for thermal imaging and remote controls.
- Visible Light: The narrow range of electromagnetic waves that can be detected by the human eye.
- Ultraviolet (UV): UV radiation is used for sterilization and can cause skin burns.
- X-rays: These waves are used in medical imaging and have high energy.
- Gamma Rays: With the highest energy, gamma rays are used in cancer treatment and come from radioactive decay.
5. Applications of Electromagnetic Waves
- Communication: Electromagnetic waves are used for radio, television, and mobile communication.
- Medical Applications: X-rays and gamma rays are used for medical imaging and cancer treatment.
- Microwave Cooking: Microwaves are used in ovens for cooking food.
- Remote Controls: Infrared waves are commonly used in remote control devices for TVs and other appliances.
- Radar: Radio waves are used in radar systems for navigation and weather monitoring.
- Satellite Communication: Electromagnetic waves are essential for satellite communication in space.