Verified Solution • 2025–26 Session moderate

QPage 338: Q1: Electromagnetic Waves Solutions — HC Verma: Concepts of Physics - Volume 2

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often incorrectly assume that all dielectric materials absorb microwaves equally or that the container heats up via induction. You must explicitly state that absorption depends on the material's natural frequency matching the microwave frequency, which is true for water but false for the plastic container.

In a microwave oven, the food is kept in a plastic container and the microwaves is directed towards the food. The food is cooked without melting or igniting the plastic container. Explain.

Step-by-Step Verified Solution

**Answer:** The food is cooked because water molecules in the food absorb microwaves at their resonant frequency. The plastic container does not absorb microwaves because its natural frequency does not match the microwave frequency. **Step-by-Step Explanation:** Microwaves have a frequency that matches the natural frequency of water molecules. When food containing water is placed in a microwave oven, the water molecules resonate and absorb energy, which is converted into heat. The plastic container is made of a material whose molecules do not resonate at the microwave frequency, so it remains unaffected and does not melt or ignite [citation:12].

All Questions in this Chapter

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