Prep ware/Test Guide

Question: The potential difference between two conductors which are insulated from each other is measured in

Answer: A- Volts (Electrical pressure is measured in volts.) Explanation: the potential difference between two conductors is a measure of the electrical pressure difference between the conductors. Electrical pressure is measured in volts.

Question: The basis for transformer operation in the use of alternating current is mutual

Answer: inductance Explanation: A transformer operates on the basis of mutual inductance. The changing current in the primary windings produces a changing magnetic field whose flux cuts across the turns of the secondary winding and induces a voltage into it.

Question: When different rated capacitors are connected in series in a circuit, the total capacitance is?

Answer: A - less than the capacitance of the lowest rated capacitor. Explanation: when capacitors of different values are connected in series, the total capacitance is less than that of the lowest rated capacitor.

Question: the opposition offered by a coil to the flow of alternating current is called (disregard resistance)?

Answer: Inductive Reactance Explanation: When alternating current flows in a coil wire, the changing lines of flux cutting across the turns of wire in the coil induce a voltage in it. The polarity of this voltage (the counter EMF) is opposite to the polarity of the voltage that caused it. The counter EMF decreases the current flowing through it. This opposition to the flow of alternating current is called inductive reactance (XL), and it is measured in ohms. It opposes the flow of current, but it does not cause heat nor use any power.

Question: a term that describes the combined resistive forces in an AC circuit is?

Answer: Impedance. Explanation: impedance, whose symbol is Z, is the combined resistive force in an AC circuit. There are three types of resistive forces in an AC circuit: inductive reactance, which causes the current to lag the voltage, capacitive reactance, which causes the current to lead the voltage, and resistance, which allows the current and voltage to remain in phase. Inductive and capacitive reactance are 180 degree out of phase, and they cancel each other. Impedance is the vector sum of the resistance and the total reactance in the circuit; it is expressed in ohms and is found by the formula: Z equal to the square root of R Squared plus X squared.

Question: working voltage of a capacitor in an AC circuit should be?

Answer: at least 50 percent Greater than the highest applied voltage Explanation: The working voltage of a capacitor is the highest voltage that can be steadily applied to it without the danger of the dielectric breaking down. The working voltage depends upon the material used as the working voltage depends upon the material used as the dielectric and on its thickness. A capacitor used in an AC circuit should have a working voltage at least 50 percent greater than the highest voltage that will be applied to it.

Question: when more than two inductors of different inductances are connected in parallel in a circuit, the total inductances.

Answer: A - less than the inductance of the lowest rated inductor. Explanation: when two or more inductors having different inductances are connected in parallel, the total inductance is less than the inductance of the lowest rated inductor.

Question: Convert farads to microfarads by

Answer: A - multiplying farads by 10 to the power of 6 Explanation: each farad is equal to 10 to the power of 6 microfarads. Example: 2 farads is equal to 2x 10 to the power of 6 (2,000,000) microfarads.

Question: An increase in which of the following factors will cause an increase in the inductive reactance of a circuit?

Answer: A- Inductance and frequency. Explanation: the inductive reactance (XL) in an AC circuit is increased when either the frequency of the alternating current or the inductance of the circuit is increased. Resistance, voltage, or capacitive reactance have no effect on the inductive reactance of a circuit.

Question: Convert farads to picofarads by:

Answer: A- multiplying farads by 10 to the power of 12 Explanation: each farad is equal to 10 to the power of 12 picofarads. Example: 2 farads is equal to 2x 10 to the power of 6 (2,000,000,000) picofarads.

Question: Unless otherwise specified, any values given for or voltage in an AC circuit are assumed to be

Answer: B- effective values Explanation: almost all measuring instruments used for electrical system servicing measure the effective (rms) values of alternating current. Unless peak values, peak-to-peak values, or average values are specifically called out, effective values are assumed.

Question: In an AC circuit, the effective voltage

Answer: B- greater than the maximum instantaneous voltage. Explanation: The effective voltage of sine wave alternating current is .707 time its peak voltage. The effective voltage, also called the root-mean-square(rms) voltage, is the voltage measured by most of the AC voltmeters. Peak voltage is measured with either a special peak voltmeter or an oscilloscope.

Question: Which effect does not apply to the movement of electrons flowing in a conductor?

Answer: C- Static Energy Explanation: Current flowing through a conductor produces a magnetic field and also dissipates thermal energy.

Question: What factors strengthen a coil inductor?

Answer: C- adding coils close together Explanation: As more loops are added close together, the strength of the magnetic field increases. Many loops close together will result in a strong electromagnet.

Question: when different rated capacitors are connected in parallel in a circuit, the total capacitance

Answer: C- equal to the sum of the individual inductances. Explanation: when capacitors are connected in parallel, the effective area of the plates add, and the total capacitance is the sum of the individual capacitances

Question: When inductors are connected in series in a circuit, the total inductance is (where the magnetic fields of each inductor do not affect the others)

Answer: C- equal to the sum of the individual inductances. Explanation: when several inductors are connected together in such a way that there is no inductive coupling, the total inductance is the sum of the individual inductances.

Question: The amount of electricity a capacitor can store is directly proportional to the?

Answer: C- plate area and inversely proportional to the distance between the plates. Explanation: Three factors affect the amount of electricity a capacitor can store: a) The area of the plates. The larger the plate area, the greater the capacity. b) The thickness of the dielectric (the distance between the plates). The closer the plates are together, the stronger the electrical field will be, and the greater the capacity. c)The material from which the dielectric is made (it's dielectric constant). The higher the dielectric constant, the greater the capacity.

Question: Electrostatic fields are also known as?

Answer: Dielectric fields. Explanation: A field of force exists around a charged body. This is an electrostatic field (Sometimes called a dielectric field) and it is represented by lines that extend in all directions from the charged body which terminate where there is an equal and opposite charge.

Question: Capacitors are sometimes used in DC circuits to

Answer: Smooth out slight pulsations in current/voltage. Explanation: capacitors store electrical charges and are sometimes used in DC circuits to smooth out slight pulsations in the current or voltage. They accept electrons when there is an excess and release them back into the circuit when the values decrease.

Question: is the opposition to the flow of AC produced by a magnetic field with generated back voltage (EMF) called?

Answer: inductive reactance Explanation: Alternating current is in a constant state of change; the effects of the magnetic fields are continuously inducted voltage opposition to the current in the circuit. This opposition is called inductive reactance, symbolized by XL, and is measured in ohms just as resistance is measured. Inductance is the property of a circuit to oppose any change in current and it is measured in henries. Inductive reactance is a measure of how much the countering EMF in the circuit will oppose current variations.