Speed of Sound — Prelims Strategy

Prelims Strategy

To effectively tackle NEET questions on the speed of sound, a multi-pronged strategy is essential. Firstly, master the fundamental formulas: $v = \sqrt{B/\rho}$ for general media and $v = \sqrt{\gamma P/\rho}$ or $v = \sqrt{\gamma RT/M}$ for gases.

Understand the meaning of each term. Secondly, memorize the key dependencies: $v \propto \sqrt{T}$ (absolute temperature) for gases, $v \propto 1/\sqrt{\rho}$ (for different gases at same T and P), and the independence from pressure (at constant T), frequency, and amplitude.

Thirdly, pay close attention to units and conversions: Always convert temperatures to Kelvin for calculations involving proportionality. For numerical problems, ensure all quantities are in SI units.

Fourthly, practice comparative questions: Be able to quickly rank speeds in solids, liquids, and gases, and understand why humidity increases speed in air. For approximation questions involving temperature changes, remember $v_T \approx v_0 + 0.

61T$. Finally, beware of trap options: Distractors often involve incorrect proportionality (e.g., linear instead of square root), incorrect temperature units (Celsius instead of Kelvin), or including frequency/amplitude as factors affecting speed.

Always re-read the question carefully to identify what is being asked and what assumptions (like constant temperature or pressure) are implied.