The method used to generate eddy currents in a test
specimen by means of a coil can most closely be
compared with the action of a:
transformer.
What happens when the electrical current in an eddy
current coil reverses direction?
The direction of the eddy currents in the test part also
reverses.
The magnetic field generated by eddy currents induced in
a test specimen:
opposes the magnetic field that induced the eddy
currents.
When is the penetration of eddy currents in a conductive
material decreased?
When the test frequency, conductivity of the
specimen, or permeability of the specimen is
increased.
At a fixed test frequency, in which of the following
materials will the eddy current penetration be greatest?
Lead (7% IACS conductivity)
A term used to describe the effect observed due to a
change in the coupling between a test specimen and a flat
probe coil when the distance of separation between them
is varied is:
liftoff.
When performing eddy current testing, under what
condition are discontinuities most easily detected?
When the eddy currents are coplanar with the major
dimension of the discontinuity.
Which of the following discontinuities is easiest to detect
with an electromagnetic test? (Assume that the area of the
discontinuity is equal in all four choices listed.)
A radial crack that extends to the outer surface of a
51 mm (2 in.) diameter bar.
What is a term used to define the timing relationships
involved in alternating current signals?
Phase
The impedance of a test coil can be represented by the
vector sum of:
inductive reactance and resistance.
What does the term “fill factor” apply to?
An encircling coil
Reference standards used for ET:
must be free of measurable discontinuities, but may
contain artificial or natural discontinuities, or may be
free of discontinuities, depending on the test system
and the type of test being conducted.
The thickness of nonconductive coatings on a conductive
base can be most simply measured by:
observing the liftoff effect caused by the coating.
Some of the products commonly tested using encircling
coils are:
rods, tubes, and wire.
It is often possible to sort various alloys of a nonmagnetic
metal using ET when:
there is a unique range of conductivity values for each
alloy.
When conducting ET on tubing with a system that
includes a frequency discriminating circuit, which of
the following variables would be classified as a highfrequency
variable?
Small discontinuities
An out-of-phase condition between current and voltage:
can exist in both the primary and secondary windings
of an eddy current coil.
For age hardenable aluminum and titanium alloys,
changes in hardness are indicated by changes in:
conductivity.
