Ultrasound is used to check for cracks inside metal parts.
A probe is placed on the top surface of a steel block. The block is 0.24 m thick. The probe sends a pulse of ultrasound down into the block and detects the echoes.
The speed of ultrasound in steel is 6000 m/s.
The Table shows the times at which two echoes are detected.
Table
| Echo | Time after pulse is sent in μs\mu\text{s}μs |
|---|---|
| echo 1 | 30 |
| echo 2 | 80 |
Show that echo 2 is from the bottom surface of the block.
Echo 1 is from a crack inside the block.
Calculate the depth of the crack below the top surface of the block.
A second steel block, with the same thickness, has no crack.
Describe how the echoes detected from this block would be different.
The ultrasound has a frequency of 5.0 MHz.
Calculate the wavelength of the ultrasound in steel.