If the frequency of a sound wave produced by an oscillating piston of a long tube filled with air is 20 Hz, then how many oscillations does the piston complete per minute? [Pg. No. 195]

Frequency means the number of oscillations completed in one second. So, a frequency of 20 Hz means the piston completes 20 oscillations per second. In one minute, there are 60 seconds, so the number of oscillations completed per minute is:

$$20 \times 60 = 1200$$

Therefore, the piston completes 1200 oscillations per minute.