In a medium where the speed of sound is 1540 m/s, what is the wavelength at 2 MHz?

In a medium where the speed of sound is 1540 m/s, what is the wavelength at 2 MHz?

• A. 0.77 mm
• B. 7.7 mm
• C. 0.077 mm
• D. 77 mm

Answer: (A)

Wavelength is found by dividing the speed of sound by the frequency. With a speed of 1540 m/s and a frequency of 2 MHz (2 x 10^6 Hz), the wavelength is 1540 / 2,000,000 = 0.00077 meters, which equals 0.77 millimeters. That matches the given value.

To see why the other numbers don’t fit: a wavelength of 7.7 mm would correspond to a frequency of about 200 kHz; 0.077 mm would correspond to about 20 MHz; and 77 mm would correspond to about 20 kHz. None of those equal 2 MHz.