Question

The condition under which a microwave oven heats up a food item containing water molecules most efficiently is -

• A. Infra-red waves produce heating in a microwave oven
• B. The frequency of the microwaves must match the resonant frequency of the water molecules.
• C. The frequency of the microwave has no relation with natural frequency of the water molecules
• D. Microwaves are heat waves, so always produce heating

Answer 1

The correct option is B The frequency of the microwaves must match the resonant frequency of the water molecules.

Water molecules are behaves as dipoles, and they oscillate in an electric field with the frequency in the range of microwaves.
The amplitude of oscillation will be maximum when the frequency of microwaves match the resonant frequency of water molecules.

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(B\right)$ is the correct answer.