Class 12 Physics chapter 8 Electromagnetic Waves

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Questions and answers ❓

1. What are electromagnetic waves?

Answer: Electromagnetic waves are waves that are formed by the oscillation of electric and magnetic fields, which are perpendicular to each other and to the direction of wave propagation. These waves do not require a medium to travel and can propagate through a vacuum.

2. Who predicted the existence of electromagnetic waves?

Answer: The existence of electromagnetic waves was predicted by James Clerk Maxwell in 1864 through his set of equations, known as Maxwell’s equations

3. What is the speed of electromagnetic waves in a vacuum?

Answer: The speed of electromagnetic waves in a vacuum is approximately (3 \times 10^8) meters per second (m/s), which is the speed of light.

4. What is the source of electromagnetic waves?

Answer: Electromagnetic waves are generated by accelerating charges, such as oscillating electric charges or currents.

5. What are the different types of electromagnetic waves?

Answer: The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

6. What is the electromagnetic spectrum?

Answer: The electromagnetic spectrum is the range of all types of electromagnetic radiation, categorized by their wavelengths or frequencies, from radio waves to gamma rays.

7. What is the significance of the displacement current?

Answer: The concept of displacement current, introduced by Maxwell, is crucial in explaining the continuity of current in circuits with time-varying electric fields, ensuring that Ampere’s law is valid even in cases where the electric field is changing.

8. Why are electromagnetic waves considered transverse waves?

Answer: Electromagnetic waves are considered transverse because the oscillating electric and magnetic fields are perpendicular to the direction of wave propagation.

9. What is the relationship between the electric and magnetic fields in an electromagnetic wave?

Answer: In an electromagnetic wave, the electric field and the magnetic field are perpendicular to each other and also to the direction of wave propagation. Their magnitudes are related and oscillate in phase.

10. What is the role of the magnetic field in electromagnetic wave propagation?

Answer: The magnetic field in an electromagnetic wave works together with the electric field to propagate the wave through space. The changing magnetic field induces a changing electric field, and vice versa, leading to the wave’s propagation.

11. Explain the concept of wave polarization.

Answer: Polarization refers to the orientation of the oscillating electric field in an electromagnetic wave. A polarized wave has its electric field oscillating in a particular direction, while an unpolarized wave has electric fields oscillating in multiple directions.

12. What are the practical applications of microwaves?

Answer: Microwaves are used in various applications, including microwave ovens for cooking, satellite communications, radar systems, and Wi-Fi technology.

13. What are X-rays and where are they commonly used?

Answer: X-rays are high-energy electromagnetic waves that can penetrate through most materials. They are commonly used in medical imaging to view the inside of the human body and in security scanners.

14. What is the significance of ultraviolet radiation?

Answer: Ultraviolet (UV) radiation has higher energy than visible light and can cause chemical reactions, such as the formation of vitamin D in the skin. However, excessive exposure can cause skin damage and increase the risk of cancer.

15. What are gamma rays, and why are they considered dangerous?

Answer: Gamma rays are the highest-energy form of electromagnetic radiation, produced by nuclear reactions and radioactive decay. They are dangerous due to their high penetrating power, which can cause severe damage to living tissues.

16. How does the Earth’s atmosphere affect electromagnetic waves?

Answer: The Earth’s atmosphere absorbs or scatters certain wavelengths of electromagnetic radiation, particularly ultraviolet rays, X-rays, and gamma rays, protecting life on Earth but also limiting the observation of celestial objects in these wavelengths.

17. What is the principle of communication using electromagnetic waves?

Answer: Communication using electromagnetic waves involves the transmission and reception of signals (such as radio waves) through antennas, where the information is encoded onto a carrier wave that travels through space.

18. Explain the concept of radiation pressure.

Answer: Radiation pressure is the pressure exerted by electromagnetic waves on a surface due to the momentum carried by the waves. It is a tiny force but significant in applications like solar sails used in space travel.

19. How are radio waves generated?

Answer: Radio waves are generated by oscillating electric charges in an antenna, typically by using an alternating current. These oscillations produce changing electric and magnetic fields that propagate as radio waves.

20. What is the significance of visible light in the electromagnetic spectrum?

Answer: Visible light is the portion of the electromagnetic spectrum that is detectable by the human eye, allowing us to perceive the world around us. It is crucial for vision and various optical technologies.

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