If frequency doubles, the wavelength will:

• A. It doubles
• B. It halves
• C. It remains the same
• D. It increases by factor of 1.54

Answer: (B)

In a fixed medium, the speed of sound is basically constant, so wavelength is tied to frequency by λ = v / f. If you double the frequency, the wavelength must become half to keep the product fλ equal to the constant speed v. For example, with v about 1540 m/s, a 5 MHz wave has a wavelength around 0.308 mm, and at 10 MHz it’s about 0.154 mm. So the wavelength halves when frequency doubles. The other options would imply the speed changed or kept the same without adjusting λ, which isn’t the case when frequency changes in the same medium.