Casting, Forming and Welding Multiple Choice Questions on “Eddy Current Test”.
1. Eddy current testing does not work below what thickness of materials?
a) 0.1 mm
b) 0.2 mm
c) 0.3 mm
d) 0.4 mm
Answer: a
Clarification: It is one of the limitations of eddy current that defects having a thickness larger than required cannot be detected using eddy current method. Conventionally eddy current method cannot detect surface defects below 0.1 mm.
2. Eddy currents are not used for the measure of which of the following properties?
a) Electrical conductivity
b) Magnetic resistivity
c) Hardness
d) Grain size
Answer: b
Clarification: The inspection of structures done by eddy current method is based on the principle of electromagnetic induction. This method of detecting defects can be used for knowing the measure of electrical conductivity, grain size, hardness and magnetic permeability.
3. Eddy current inspection method cannot be detect which of the following defect?
a) Laps
b) Seams
c) Voids
d) Surface crack
Answer: d
4. Small drilled hole was a reference calibration in eddy current testing because it was produced in precise sizes.
a) True
b) False
Answer: a
Clarification: For making perfect measurements and calculations, a few artificial defects were tried and a small hole was selected as the standard. The small drilled hole was selected because, it was not just easy to produce, but also, it was produced in precise sizes.
5. What is the heat generated in eddy current operations?
a) VI
b) VIR
c) I2RT
d) I2R
Answer: d
Clarification: Eddy current method of inspection and heating techniques is used for metal heating. The heat generated by this method can be given by I2R, I is current and R is the resistance.
6. The signal display of eddy current system does not take place on which of the following media?
a) Oscilloscope
b) Oscillograph
c) Electric tape
d) Magnetic tape
Answer: c
Clarification: Eddy current method is used as a non-destructive technique. Most of the times, a magnetic tape is used or a oscilloscope or an oscillograph, but not an electric tape.
7. Multi frequency testing allows to overcome problems in eddy current testing.
a) True
b) False
Answer: a
Clarification: It is one of the limitations of eddy current testing that, below a certain thickness of the surface defect, the defect cannot be detected. This particular problem can be overcome by using multifrequency testing.
8. For measuring glue line thickness between aluminium sheets, what should the thickness of the sheet be?
a) 1.2 mm
b) 1.4 mm
c) 1.6 mm
d) 1.8 mm
Answer: c
Clarification: For measuring the glue line thickness of aluminium sheets using eddy current method, initially the surface has to be vitally cleaned. The thickness of the aluminium sheet for calculating glue line thickness is 1.6mm.
9. What is the conductivity of a 7075-T6 aluminium sheet with an average thickness of 1.6 mm?
a) 30 IACS
b) 31 IACS
c) 32 IACS
d) 33 IACS
Answer: b
10. With an increase in the density of the material who does it affect the power loss in eddy current?
a) Increases
b) Decreases
c) Does not change
d) Not related
Answer: b
Clarification: According to the power dissipation formula for eddy currents, power loss experienced is inversely related to the density of the material, that is, with an increase in the density of the material, there is a decrease in the power loss.