An engineer uses ultrasound to test three bonded layers, A, B and C, of a pipe coating. The ultrasound travels from A into B and then into C. Its frequency remains constant. The speed of the ultrasound in B is three times its speed in A. Its speed in C is half its speed in B.
The wavelength in C is 0.72 mm.
What is the wavelength in A?
0.36 mm0.36\ \mathrm{mm}0.36 mm
1.08 mm1.08\ \mathrm{mm}1.08 mm
0.24 mm0.24\ \mathrm{mm}0.24 mm
0.48 mm0.48\ \mathrm{mm}0.48 mm