This set of Testing of Materials Multiple Choice Questions & Answers (MCQs) focuses on “Eddy Current Inspection & Ultrasonic Testing”.
1. What principle defines eddy current inspection (ECI)?
a) Lenz law
b) Biot-Savart Law
c) Electromagnetic induction principle
d) Faraday’s law
View Answer
Explanation: ECI is based on the principle of electromagnetic induction. In this eddy currents are induced within metal as a coil carrying AC is brought in proximity.
2. Eddy current inspection (ECI) is generally restricted to a depth below ___________
a) 1µm
b) 1mm
c) 2mm
d) 6mm
View Answer
Explanation: Eddy current inspection is generally restricted to a depth below 6mm, It is because of the secondary induced current in the material and it also called as skin effect.
3. What is the main reason for the limitation of depth below 6mm in Eddy current inspection (ECI)?
a) Surface coating
b) Electron hole pair generation
c) Skin effect
d) Residual stresses
View Answer
Explanation: Eddy current causes skin effect. It restricts to a depth below 6mm. Skin effect is the reason for the limitation of depth below 6mm in ECI.
4. The total resistance of the coil in Eddy current inspection (ECI) is known as __________
a) Impedance
b) Inductance
c) Reactance
d) Capacitance
View Answer
Explanation: Alternating current in the coil is opposed by 2 factors. Namely ohmic resistance and inductive reactance which is combinely known as impedance.
5. The density of eddy current ____________ with distance from the surface in center.
a) Increase linearly
b) Increase exponentially
c) Decrease linearly
d) Decrease exponentially
View Answer
Explanation: The density of eddy current decrease exponentially with distance from the surface in the center. It is known as the skin effect.
6. Eddy current inspection is only used for ferromagnetic materials.
a) True
b) False
View Answer
Explanation: Eddy current inspection exploits the electrical conductivity of the material but not the magnetic properties. It can be used for all metals that has considerable electrical conductivity.
7. Standard penetration depth varies from material to material.
a) True
b) False
View Answer
Explanation: Standard penetration depth is different for different materials. It is not even constant for a given material.
8. What is acoustic impedance (in MPa s/m) of aluminum?
a) 1.58
b) 45.72
c) 16.77
d) 41.08
View Answer
Explanation: Aluminum has acoustic impedance 16.77 MPa s/m. It is greater than oil while less than steel and copper.
9. Which of the following is the poorest transmitter of sound?
a) Oil
b) Water
c) Air
d) Copper
View Answer
Explanation: Air is the poorest transmitter of sound. It has acoustic impedance 4.04 × 10-4 MPa s/m.
10. Which of the following is the best transmitter of sound?
a) Oil
b) Aluminum
c) Steel
d) Copper
View Answer
Explanation: Steel is the best transmitter of sound among four. It has acoustic impedance 45.72 MPa s/m.
11. What is the drawback of ultrasonic testing?
a) Low depth
b) High sensitivity
c) Shape restriction
d) Higher errors
View Answer
Explanation: Ultrasonic testing can be performed on any shape specimen. It has high sensitivity. Higher depth can be tested.
12. What is a type of piezoelectric crystal?
a) Natural
b) Normal
c) Angle
d) Transverse
View Answer
Explanation: Piezoelectric crystals are of two types. These are natural and artificial based on their source.
13. The object under ultrasonic inspection must have parallel surfaces.
a) True
b) False
View Answer
Explanation: The object under inspection must have parallel surfaces. It is a drawback of an ultrasonic method.
14. Ultrasonic testing is destructive testing?
a) True
b) False
View Answer
Explanation: Ultrasonic testing is non-destructive testing. It can be performed on finished and assembled materials.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
To practice all areas of Mechanical Behaviour & Testing of Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.
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