An ultrasonic thickness gauge (UTG) uses ultrasound waves to determine the thickness of solid materials. Figure 7 shows the UTG on a copper block of thickness x. Figure 7 copper block UTG. ultrasound intensity 0 The UTG emits a very short pulse of ultrasound into the block at P. The UTG then detects the waves reflected from Q. Figure 8a P Multiple reflections occur at the surfaces of the block as shown in Figures 8a and 8b. The paths of the waves are vertical but are shown at an angle for clarity. 2 A QBOASENSIT WW2HA Figure 9 shows the variation of ultrasound intensity with time as detected by the UTG. Figure 9 4 6 time / s X P Figure 8b Vi- 8 10 Peak A is detected when the pulse reflects once at Q as shown in Figure 8a. Peak B is detected when the pulse reflects twice at Q as shown in Figure 8b. Peaks C and D are produced by further reflections at Q. 2 The speed of the ultrasound in the block is 4660 m s.bir grow ristox Determine x. The UTG is used to measure the thickness of a painted copper pipe. comp Figure 10 shows the UTG on the outer surface of the pipe. The figure also shows two paths R and S taken by the ultrasound. The paint has a depth d and the pipe wall has a thickness y. Figure 10 paint copper air UTG. RT S not to scale The speed of ultrasound in the paint is much less than in copper. Blogg 3 An engineer uses the timing for path R to determine y. Explain why the engineer's determination of y is not accurate.To butbe auf 4 An accurate determination of y can be made by analysing reflections R and Show that the path difference between R and S is independent of d.