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
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. ECI is generally restricted to a depth below ___________
Explanation: Eddy current inspection is generally restricted to a depth below 6mm. It is because of skin effect.
3. What is the reason for limitation of depth below 6mm in ECI?
a) Surface coating
b) Electron hole pair generation
c) Skin effect
d) Residual stresses
Explanation: Eddy current causes skin effect. It restricts to a depth below 6mm. Skin effect is the reason for limitation of depth below 6mm in ECI.
4. The total resistance of the coil of ECI is known as __________
Explanation: Alternating current in the coil is opposed by 2 factors. Namely ohmic resistance R and inductive reactance.
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
Explanation: The density of eddy current decrease exponentially with distance from the surface in the center. It is known as skin effect.
6. ECI is only used for ferromagnetic materials.
Explanation: ECI doesn’t require magnetic conduction. It is effective for both ferromagnetic and non-magnetic materials.
7. Standard penetration depth varies from material to material.
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?
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?
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?
Explanation: Steel is the best transmitter of sound among four. It has acoustic impedance 45.72 MPa s/m.
11. What is drawback of ultrasonic testing?
a) Low depth
b) High sensitivity
c) Shape restriction
d) Higher errors
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?
Explanation: Piezoelectric crystals are of two types. These are natural and artificial based on their source.
13. The object under inspection must have parallel surfaces.
Explanation: The object under inspection must have parallel surfaces. It is a drawback of an ultrasonic method.
14. Ultrasonic testing is destructive testing?
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.