Question

Explain the following giving reasons:
(i) Electromagnetic waves differ considerably in their mode of interaction with matter.
(ii) Food items to be heated in microwave ovens must contain water.
(iii) Welders wear face mask with glasses during welding.

Hint:

Electromagnetic waves' interaction with matter depends on their frequency, which dictates their energy and the mode of absorption.

Answer 1

Explanation with Reasons 

(i) Electromagnetic Waves Differ Considerably in Their Mode of Interaction with Matter Electromagnetic waves cover a wide spectrum, ranging from radio waves to gamma rays. The way they interact with matter depends on their frequency and wavelength: 
1. Low-frequency waves (e.g., radio waves) can pass through materials like air, glass, and other non-metallic substances because their energy is not high enough to excite electrons or cause significant atomic or molecular transitions.
2. High-frequency waves (e.g., UV rays, X-rays, and gamma rays) have enough energy to ionize atoms or molecules, leading to chemical reactions or causing ionization, which is harmful and potentially dangerous. Therefore, electromagnetic waves interact with matter differently depending on their energy content, which varies with frequency and wavelength. 

(ii) Food Items to Be Heated in Microwave Ovens Must Contain Water Microwave ovens work by emitting electromagnetic waves with a frequency typically around 2.45 GHz. These microwaves are absorbed by water molecules in food. The microwaves cause the water molecules to rotate rapidly, generating heat through friction. Since water has a high dielectric constant, it absorbs microwaves effectively, heating the food. Foods without water, like dry bread or certain snacks, do not absorb microwaves efficiently, so they do not heat up well. Therefore, food items with water are best suited for microwave heating. 

(iii) Welders Wear Face Mask with Glasses During Welding During welding, the intense light and ultraviolet radiation emitted can cause severe damage to the eyes, resulting in conditions like welder’s flash or arc eye. These conditions are similar to sunburn but affect the eyes, causing pain, inflammation, and even long-term damage. The face mask with protective glasses worn by welders serves to block harmful UV rays and visible light from the welding arc, protecting their eyes from injury. The lenses in the welding glasses are specifically designed to filter out harmful radiation while allowing sufficient light for visibility, ensuring both safety and clarity during the welding process.