QUESTIONS AND VERIFIED SOLUTIONS LATEST UPDATE THIS
YEAR
Whenever ? flows through a conductor, a magnetic field is created. - ANSWER-
current
The ability of a moving or changing magnetic field to induce a voltage into a
conductor is called ? . - ANSWER-inductance
When a conductor that is cutting through a magnetic field changes direction, the ?
of the induced voltage will be reversed. - ANSWER-polarity
If the current flowing through a conductor decreases, the magnetic field around the
conductor will increase. - ANSWER-false
Another term for counter EMF is ? EMF. - ANSWER-back
Lenz's Law states, "An induced voltage or current opposes the motion that created
the induced voltage or current." - ANSWER-true
The induced voltage is ? out of phase with the applied voltage. - ANSWER-180
degrees
Maximum EMF is induced when a conductor cuts a magnetic field at ? . -
ANSWER-90 degrees and 270 degrees
Cutting more magnetic lines of force per second will increase the amount of
voltage induced into a conductor. - ANSWER-true
1
,When there is no current flowing through a conductor, the magnetic field around
the conductor is ? . - ANSWER-not present
The unit of inductance is called the ? . - ANSWER-Henry
When a coil induces a voltage into itself, it is known as ? inductance. - ANSWER-
self
The ability of one coil to induce a voltage into another coil is called ? induction. -
ANSWER-mutual
A coil of wire wrapped around a core is called a(n) ? . - ANSWER-inductor
For a voltage to be induced in a conductor, there must be relative motion between
the conductor and a magnetic field. - ANSWER-true
The ability of a current-carrying conductor, coil, or circuit to induce a voltage into
itself or adjacent circuits is called ? . - ANSWER-inductance
The letter ? is used in calculations to represent inductance. - ANSWER-L
A transformer operates under the principle of ? . - ANSWER-mutual induction
The inductance of a coil is directly related to the number of turns of wire that make
up the coil. - ANSWER-true
2
,The flux lines that do not link to all the other coils do not contribute to the total
inductance, and are called ? flux. - ANSWER-leakage
The ability of a material to focus, or concentrate, magnetic lines of force is called
magnetic ? . - ANSWER-permeability
If an iron core is inserted into a coil, the inductance of the coil will decrease. -
ANSWER-false
Moving a magnetic field across a stationary conductor will not induce a voltage in
the conductor. - ANSWER-false
Inductance has no effect on a DC circuit as long as the current is constant. -
ANSWER-true
All cables and wires contain some resistance. When a current flows through them,
a(n) ? will occur. - ANSWER-voltage drop
A distribution transformer delivers 248 volts at the secondary bushings while a few
spans away, the secondary voltage is 224 volts. The voltage drop between these
two points is ? . - ANSWER-24v
If the size of the feeder wires is increased for a given load, the line voltage drop
will ? . - ANSWER-decrease
Line (voltage) drop is equal to the current through the line multiplied by the
resistance of the line as expressed in the formula Eline = Iline × Rline. -
ANSWER-true
3
, Two wires off a main feeder supply current to a transformer several spans away.
The voltage of the feeder at the point of take-off is 2,440 volts. The resistance of
the two wires is two ohms and the transformer draws 40 amperes. The line loss
(voltage drop) is ? , and the voltage at the transformer is ? . - ANSWER-
80v/2,360v
The National Electric Code requires that cables and wires be chosen so that the
voltage drop from either feeder or branch circuits to the farthest outlet does not
exceed ? . - ANSWER-3%
The National Electric Code recommends that the combined voltage drop for branch
circuits and feeders not exceed ? . - ANSWER-5%
Voltage drop will increase if the ? . - ANSWER-length of the wire is increased
The resistivity constant of a conductor is determined by the ? . - ANSWER-
material from which the conductor is made
The voltage drop per thousand feet of 1 AWG copper wire (resistance = 0.154
ohms per 1,000 feet) when 50 amperes of current are flowing is ? . - ANSWER-
7.7v
The formula used to determine the resistance of a conductor is R = ? . - ANSWER-
(K × L) ÷ A
The resistance of a 6,000-foot piece of 1/0 copper wire is ? . (K for copper = 10.4;
1/0 wire = 105,600 CM) - ANSWER-.59 ohms
4