Pg:- 106,107,108
Ch:- 6
Electromagnetic radiation (EMR) refers to the energy transmitted through space in the form of electromagnetic waves. These waves are oscillations of electric and magnetic fields, which travel through a vacuum or a medium at the speed of light.
Key Characteristics of Electromagnetic Radiation:
Dual Nature: EMR exhibits both particle-like and wave-like behavior, known as wave-particle duality. It can be described as waves or as particles called photons.
Speed: In a vacuum, EMR travels at the speed of light, approximately 3×10^8 m/s.
Frequency and Wavelength:
Frequency (ν) is the number of wave cycles per second, measured in hertz (Hz).
Wavelength (λ) is the distance between consecutive peaks of the wave, typically measured in meters.
The relationship is given by c=νλ, where c is the speed of light.
Energy: The energy of EMR is directly proportional to its frequency, given by E=hν, where h is Planck's constant (6.626 × 10^−34 J·s).
Electromagnetic Spectrum
The spectrum is categorized by wavelength or frequency and includes:
Radio Waves: Long wavelengths, used in communication (e.g., radio, TV).
Microwaves: Used in cooking and satellite transmissions.
Infrared (IR): Heat radiation; used in thermal imaging.
Visible Light: The only part of the spectrum visible to the human eye (ROYGBIV).
Ultraviolet (UV): Causes sunburn; used in sterilization.
X-Rays: Used in medical imaging.
Gamma Rays: High-energy radiation, often from radioactive decay, used in cancer treatment.
Applications of EMR
Communication: Radio, TV, mobile phones, Wi-Fi.
Medicine: X-rays, laser surgery, radiation therapy.
Industry: Remote sensing, material heating, and manufacturing.
Astronomy: Observing stars and galaxies in different EM spectrum bands.
Everyday Technology: Cameras, remote controls, and more.
1. Explain how electromagnetic radiation is used in medical imaging, specifically in X-rays, and discuss the safety measures taken to protect patients from its high energy.
2. A Wi-Fi signal operates at a frequency of 2.4 GHz. Calculate its wavelength and explain how this frequency is suitable for data transmission over short distances.
(Use the relationship , where is the speed of light.)
3. Describe the role of infrared radiation in thermal imaging. Why is infrared radiation particularly effective for this application?
4. Ultraviolet (UV) radiation is commonly used for sterilization purposes. Explain how UV radiation kills bacteria and viruses and why it is not suitable for all types of sterilization.
5. Astronomers use various parts of the electromagnetic spectrum to observe celestial bodies. Discuss why gamma rays and X-rays provide unique information about stars and galaxies compared to visible light.