An ultrasonic flaw detector sends a short pulse into a steel plate. The speed of sound in steel is 5000m/s. The pulse is emitted at time t=0. The first reflected echo from the far surface is received at t=0.0008s, while a second echo from an internal crack is received at t=0.0005s.
(i) Calculate the thickness of the steel plate.
(ii) Determine the distance of the crack from the surface where the pulse was introduced.
(iii) State any two advantages of using ultrasonic testing for detecting internal defects in metals.