## Questions & Answers - Electromagnetic Testing (ET) Level - 1 - 2 - 3

by Edward A. Ginzel *
Acknowledgement:
Materials Research Institute Canada are thanked for permission to use their
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 Level 1 Question [Ref] 1 Eddy current testing requires that the material tested be [ECM] a) magnetic b) non-magnetic c) conductive d) both b and c 2 An oscillator used in generating time varying current in an ECT instrument usually supplies currents at frequencies from [ECM] a) 1 Hz to 20 kHz b) 50 Hz to 60 Hz c) 1 kHz to 2 MHz d) 0.5 MHz to 4 GHz 3 The eddy current probe is most simply a [ECM] a) coil of copper wire b) semiconductor c) capacitor d) ceramic resistor 4 Critical to the principles of eddy current testing is the understanding that [ECM] a) all materials conduct electricity b) all current flow has associated with it a magnetic field c) only ferro electric materials conduct eddy currents d) copper wire is used for all probe coils 5 The magnitude of magnetic flux density associated with current flowing in a conductor varies with position and current. Magnetic flux density is therefore a(n) [ECM] a) vector quantity b) scalar quantity c) square wave quantity d) unknown quantity 6 The magnetic flux density associated with a current carrying conductor _________ with increasing distance from the conductor. [ECM] a) increases b) decreases c) wobbles d) remains constant 7 The Weber (Wb) is the unit of [ECM] a) magnetic flux b) magnetic flux density c) eddy current intensity d) the Hall effect 8 When a magnetic flux near a conductor is caused to change (as when a magnet is moved past a coil) the result is [Burns] a) an increased resistance in the coil wire b) and induced voltage c) de-magnetization of the magnet d) phase reversal 9 According to Ohm's Law, in any electrical circuit, the voltage divided by the circuit impedance is equal to [ECM] a) magnetic flux density b) capacitance c) current flow d) phase angle 10 When an alternating voltage induces an EMF, the induced EMF in opposition to the change causing it. This is a statement of [Burns] a) Faraday's Law b) Lenz's Law c) Snell's Law d) Eddy's Law of Voltage 11 Eddy currents are so named because [ECM] a) of the Canadian match manufacturer that discovered them b) of the circular probes required to induce them c) of their circular paths d) small swirl patterns form on the surface domains and crystal structure 12 A device which stores electrical energy within a specified volume is a(n) [Ramshaw] a) inductor b) capacitor c) conductor d) resistor 13 The field that couples an eddy current probe and a test piece causes eddy currents to flow by [ECM] a) resonance b) induction c) friction d) the Bernoulli effect 14 The region around a magnet where its magnetic effects can be detected is called the [Jacobowitz] a) near zone b) induction zone c) magnetic field of force d) electro-magnetic region of influence 15 In a fixed magnetic field, a compass needle would arrange itself [Jacobowitz] a) parallel to the lines of force b) perpendicular to the lines of force in the plane of the field c) perpendicular to the lines of force at right angles to the plane of the field d) 45ø to the field lines 16 The location where magnetic lines of flux are considered to leave a magnet is [Jacobowitz] a) the north pole of that magnet b) the south pole of that magnet c) dependent on the position of the earth's magnetic pole d) called Domain Centre 17 The location where magnetic lines of flux are considered to enter a magnet is [Jacobowitz] a) the north pole of the magnet b) the south pole of the magnet c) dependent on the position of the sun d) called domain centre 18 Direct current can be used to induce eddy currents if [Handbook] a) the test piece is moved cyclically near the current carrying conductor b) the current carrying conductor is moved cyclically near the test piece c) either a or b d) the diameter of the conductor is less than 1/10 the thickness of the test piece 19 The rate of flow of electric charge defines [Jacobowitz] a) voltage b) coulomb c) electric current d) impedance 20 1 mA can also be written as [Jacobowitz] a) 0.01 A b) 0.001 A c) 100 æA d) 1000 MA 21 A sample which has a very low resistance will also have very high [Jacobowitz] a) resistivity b) conductivity c) conductance d) impedance 22 Compared to conductive wires, insulators are considered to have [Jacobowitz] a) very high resistance b) very low resistance c) about the same resistance d) high conductance 23 Resistance of a conductor is usually given at a specified temperature. Correction for resistance at other temperatures is obtained by using [Jacobowitz] a) liquid nitrogen b) the temperature coefficient of resistance c) vacuum or bell chambers d) matching circuits 24 Increasing the temperature of an aluminium test specimen form 20øC. to 40øC. will result in ___________ specimen resistivity. [ECM] a) no change to b) doubling c) halving d) a slight increase in 25 Eddy currents are normally induced in a sample such that they are [ECM] a) parallel to the coil windings b) parallel to the sample surface c) limited to the area of inducing field d) all of the above 26 Decrease in eddy current flow with increasing depth from the surface is known as [ECM] a) absorption b) the Hall effect c) the skin effect d) the edge effect 27 The pickup (receiver) coil of an eddy current probe is [Handbook] a) always the same coil as the magnetizing coil b) identical in diameter to the magnetizing coil c) coincident in position to the magnetizing coil d) of any size, position or even configuration 28 Heat generation associated with eddy current testing of magnetic materials is a result of [Handbook] a) dispersion and diffraction b) ohmic or resistive losses c) hysteresis losses d) both b and c 29 What is the difference between electric currents and eddy currents on the atomic level? [Handbook] a) there is no difference b) direction of electron flow c) no magnetic field is associated with electric current d) eddy currents do not occur in semi conductors 30 Current flowing in the eddy current transducer would be considered [Handbook] a) eddy current b) magnetizing currents c) back EMF d) all of the above

#### References (NDT TestMaker software)

1. [Handbook] ASNT; Nondestructive Testing Handbook, vol. four, Electromagnetic Testing, Second Edition, ASNT, 1986
2. [Jacobowitz] Jacobowitz,H.; Electricity Made Simple, Doubleday & Company, 1959
3. [Mix] Mix, P.E.,; Introduction to Non-Destuctive Testing, John Wiley & Sons, 1987
4. [ECM] V.S.Cecco, G.van Drunen and F.L.Sharp, Eddy Current Manual vol. 1, Chalk River Nuclear Laboratories, 1983
5. [Burns] D.M.Burns & S.G.G.MacDonald Physics for Biology and Premedical Students, Addison-Wesley Publishing Company, 1970
6. [Ramshaw] R.S.Ramshaw & R.G.van Heeswajk, Electromagnetic Fields and Forces University of Waterloo, Standford Educational Press, 1979
7. [Blitz] J.Blitz, Electrical and Magnetic Methods of Nondestructive Testing, Adam Hilger, IOP Publishing Ltd., 1991
8. [Techniques] D.E.Bray and D.McBride, Nondestructive Testing Techniques John Wiley & Sons, 1992
9. [Gardner] W.E.Gardner, Editor, Improving the Effectiveness and Reliability of Nondestructive Testing Pergamon Press, 1992
10. [ASME] American Society of Mechanical Engineers, ASME Section V, The American Society of Mechanical Engineers, 1992

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