1: Sound

Question 1

What property of a metal makes the propagation of ultrasonic waves possible?

Answer 1

Elasticity

Question 2

Define cycle:

Answer 2

A particle displaced from rest position…. etc

Question 3

Define frequency:

Answer 3

Number of cycles per second

Question 4

Define wavelength:

Answer 4

Distance a wave travels during a cycle OR distance between 2 particles in same state of motion

Question 5

What is the formula that relates velocity, frequency and wavelength?

Answer 5

LAMBDA = V/f

Question 6

What is the approximate ratio of velocities of sound in steel as compared to water?

Answer 6

Sounds travels approx. 4X faster in steel than in water.

Question 7

In theory, what is the smallest defect that an ultrasonic inspection can usually detect?

Answer 7

Approximately half a wavelength (LAMBDA/2)

Question 8

What is meant by “period” of a cycle?

Answer 8

Time required to complete 1 cycle.

Question 9

What is the maximum frequency that a human ear can hear?

Answer 9

20 KHz

Question 10

What is the range of frequencies used in ultrasonic testing?

Answer 10

0.5 MHz to 25 MHz

Question 11

What are the 2 factors that determine the velocity of a longitudinal wave in a medium?

Answer 11

Density and elasticity

Question 12

What’s another name for a longitudinal wave?

Answer 12

Compression wave

Question 13

What’s another name for a transverse wave?

Answer 13

Shear wave

Question 14

What’s another name for a surface wave?

Answer 14

Rayleigh wave

Question 15

What’s another name for a plate wave?

Answer 15

Lamb wave

Question 16

What is approximate ratio of velocities of shear waves to longitudinal waves in a material?

Answer 16

Shear are approximately half the velocity of a longitudinal

Question 17

What is the approximate ratio of velocities of surface waves to shear waves?

Answer 17

Surface waves are 3-15% slower than shear waves

Question 18

What is the intensity of a surface wave at a depth of 1 wavelength below the surface?

Answer 18

Approx 4% or 1/25th intensity of wave at surface

Question 19

What is the particle motion in surface waves?

Answer 19

Elliptical

Question 20

What depth do surface waves usually penetrate?

Answer 20

About 1 wavelength in material.

Question 21

What 5 factors influence velocity of a plate wave?

Answer 21

1. Type of material
2. Thickness of material
3. Frequency of wave
4. Angle if incidence of wave
5. Mode of wave generated

Question 22

What are the 2 most common types of lamb waves?

Answer 22

Symmetrical and asymmetrical

Question 23

What type of waves can propagate in solids?

Answer 23

Compression, shear, surface and plate waves

Question 24

What type of waves can propagate in liquids?

Answer 24

Only compression waves.

Question 25

Under which conditions will a surface wave reflect back to the probe?

Answer 25

Surface discontinuities, grease, oil, or dirt.

Question 26

Define the term “angle of incidence.”

Answer 26

Angle at which an incident wave strikes an interface.

Question 27

What is meant by “normal incidence”?

Answer 27

Incident wave that strikes the interface at angle of 90 degrees.

Question 28

What is condition necessary to produce reflection at an interface?

Answer 28

Sound waves hits an interface between 2 materials of different acoustic impedances

Question 29

If the angle of incidence is known, how is the angle of reflection determined?

Answer 29

Equal to angle of incidence

Question 30

What are the 2 characteristics of a material that determine its acoustic impedance?

Answer 30

Density and velocity

Question 31

What symbol is used to represent density?

Answer 31

Rho (p)