NON DESTRUCTIVE TEST

$3.$When does total destructive interference occur with two ultrasonic waves?

a$.$ When two ultrasonic beams are transmitted in parallel

b$.$ When the two ultrasonic waves are $180$ out of phase

c$.$ When the two ultrasonic waves are $360$ out of phase

d$.$ When the two ultrasonic waves are $90$ out of phase

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$4.$In Phase Array terminology, 'pitch' refers to

a$.$ The protective coating on the face of a transducer

b$.$ The distance between adjacent element centres

c$.$ The angle a wedge is machined to

d$.$ The distance between adjacent elements