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Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

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Q2-17 A change in echo amplitude from 20% of FSH to 40% of FSH is a<br />

change of how many dB?<br />

Answer: ΔdB= 20log(20/40) = 6dB drop or -6dB.<br />

Q2-20 What is the lens radius of curvature is needed in order to have a 20mm<br />

diameter 5MHz transducer focus in water at a distance of 40mm drom the<br />

lens face?<br />

Answer:<br />

R=F(n-1/n), n= V Lens /V water , n= 2.67/1.49= 1.792.<br />

R=40(0.792/1.792) = 17.7mm

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