6. The sound level is defined as β = 10log10(I/I0), where I0 = 1.00×10⁻¹² (W/m²). A point source emits sound waves with an average power output of 7.5×10⁻⁹ W. Calculate the sound level 10 meters from the source and the sound level 15 meters from the source. What is the difference in sound level (in decibels). (A) 0 (B) 2.44 (C) 3.52 (D) 4.79

10. The number of collisions a molecule makes per second is called collision frequency. At one atmosphere and 0 °C, estimate the collision frequency of air molecules. [The diameter of an air molecule under one atmosphere and 0 °C is approximately 3×10⁻¹⁰ (m), the average molecular speed is approximately 460 (m/s), and the molecular number density is approximately 2.7×10²⁵ molecules/m³]. (A) 3.5×10⁵ (collisions/s) (B) 3.5×10⁷ (collisions/s) (C) 3.5×10⁹ (collisions/s) (D) 3.5×10¹¹ (collisions/s)

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