Which combination of air conditions allows sound to travel fastest: warm and humid air, warm and dry air, cold and humid air, or cold and dry air?

• A. Warm and dry air
• B. Warm and humid air
• C. Cold and humid air
• D. Cold and dry air

Answer: (B)

Verified step by step guidance

1. Understand that the speed of sound in air depends primarily on the temperature and the composition of the air, including humidity.
2. Recall that sound travels faster in warmer air because the molecules have more energy and can transmit vibrations more quickly. Mathematically, the speed of sound in air increases with temperature approximately as \(v = v_0 \sqrt{\frac{T}{T_0}}\), where \(T\) is the absolute temperature.
3. Recognize that humidity affects the speed of sound because water vapor is less dense than dry air (which is mostly nitrogen and oxygen). Adding water vapor decreases the average molecular mass of the air mixture, which increases the speed of sound.
4. Combine these effects: warm air increases speed due to higher temperature, and humid air increases speed due to lower density. Therefore, warm and humid air allows sound to travel fastest.
5. Conclude that among the given options, the combination of warm and humid air results in the highest speed of sound.