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Basic Electrical Questions Answers

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Herein, we have covered basic Electrical questions related to Electrical Theory, Electric Circuits, Magnetism, and Power in detail.

Electrical Theory

  1. State the three fundamental parts of an atom and identify their states of charge.
  • The three fundamental particles contained in atoms are protons, neutrons, and electrons.
  • A proton is a particle contained in the nucleus of an atom that has a positive electrical charge.
  • A neutron is a particle contained in the nucleus of an atom that has no electrical charge.
  • An electron is a negatively charged particle that whirls around the nucleus at great speed in shells.
  1. Define and describe conductors, insulators, and semiconductors.
  • A conductor is a material that has very little resistance and permits electrons to move through it easily. By applying a negative charge to one side of the conductor and a positive charge to the other side of the conductor, electrons are forced to move through the conductor.
  • An insulator is a material with an atomic structure that allows few free electrons to pass through it. Insulators offer high resistance to electron flow and do not conduct electricity very well.
  • Semiconductor materials fall between the low resistance offered by a conductor and the high resistance offered by an insulator.
  • Doping is the addition of impurities to the crystal structure of a semiconductor. In doping, some of the atoms in the crystal are replaced with atoms of other materials. The addition of new atoms in the crystal structure creates N-type material and P-type material.
  • N-type material is material created by doping a region of a crystal with atoms of a material that have more electrons in their outer shells than the crystal. Adding these atoms to the crystal results in more free electrons. Free electrons (carriers) support current flow.
  • P-type material is material with empty spaces (holes) in its crystal structure. To create P-type material, a crystal is doped with atoms of a material that have fewer electrons in their outer shells than the crystal. The holes are filled with free electrons when the voltage is applied, and the free electrons move from negative potential to positive potential through the crystal.
  1. State the operating function of a diode in a circuit.
  • A diode is an electronic component that allows current to pass through it in only one direction. This is made possible by the doping process, which creates N-type material and P-type material in the same component.
  • When the voltage is applied to a diode, the action occurring in the depletion region either blocks current flow or passes current.
  • Electrons flow from the cathode to the anode, or against the triangle when a diode is in forward bias. When a negative polarity is applied to the anode and a positive polarity is applied to the cathode, the diode is in reverse bias and there is no electron flow.
  1. State the two forms of energy and give examples of each.
  • The two forms of energy are potential energy and kinetic energy. The sources of energy used to produce electricity are coal, nuclear power, natural gas, and oil.
  • Potential energy is the stored energy a body has due to its position, chemical state, or physical condition. For example, water behind a dam has potential energy because of its position. A battery has potential energy based on its chemical state. A compressed spring has potential energy because of its physical condition.
  • Kinetic energy is the energy of motion. Examples of kinetic energy include falling water, a rotating motor, or a released spring. Kinetic energy is released potential energy. The energy released when water falls through a dam is used to generate electricity. The energy released when a battery is connected to a motor is used to produce a rotating mechanical force. The energy released by a compressed spring is used to apply a braking force on a motor shaft.
  1. Define voltage and state its unit of measure and common abbreviation.
  • Voltage (E) is the amount of electrical pressure in a circuit. Voltage is also known as electromotive force (EMF) or potential difference. Voltage is produced when electrons are freed from atoms.
  • Voltage is measured in volts (V).
  • The voltage may be produced when electrons are freed from atoms by electromagnetism (generators), heat (thermocouples), light (photocells), chemical reaction (batteries/fuel cells), pressure (piezoelectricity in strain gauges), and friction (static electricity).
  • Voltage is either direct current (DC) or alternating current (AC). DC voltage is the voltage that flows in one direction only. AC voltage is the voltage that reverses its direction of flow at regular intervals. DC voltage is used in almost all portable equipment (automobiles, golf carts, flashlights, cameras, etc.). AC voltage is used in residential, commercial, and industrial lighting and power distribution systems.
  1. Define current and state its unit of measure and common abbreviation.
  • Current (I) is the amount of electrons flowing through an electrical circuit.
  • Current is measured in amperes (A).
  • Different voltage sources produce different amounts of current. For example, standard AAA, AA, A, C, and D size batteries all produce 1.5 V, but each size is capable of delivering a different amount of current. Size AAA batteries are capable of delivering the smallest amount of current, and size D batteries are capable of delivering the highest amount of current.
  • Current may be direct current or alternating current. Direct current (DC) is current that flows in only one direction. Alternating current (AC) is current that reverses its direction of flow at regular intervals.
  1. Define resistance and state its unit of measure and common abbreviation.
  • Resistance (R) is the opposition to the flow of electrons.
  • Resistance is measured in ohms.
  • The Greek letter omega (Q) is used to represent ohms. Higher resistance measurements are expressed using prefixes, as in kilohms (kQ) and megohms (MQ).
  • Resistance limits the flow of current in an electrical circuit. The higher the resistance, the lower the current flow. Likewise, the lower the resistance, the higher the current flow.
  • A conductor with a large cross-sectional area has less resistance than a conductor with a small cross-sectional area.
  1. Determine an unknown voltage, current, and resistance with Ohm’s law.
  • Ohm’s law is the relationship between voltage, current, and resistance in a circuit. Any value in this relationship can be found when the other two values are known.
  • Ohm’s law states that voltage (E) in a circuit is equal to current (I) times resistance (R).
  • Ohm’s law states that current (I) in a circuit is equal to the voltage (E) divided by resistance (R).
  • Ohm’s law states that resistance (R) in a circuit is equal to the voltage (E) divided by current (I).

Circuits

  1. Calculate resistance at any point in a series or parallel circuit.
  • The total resistance in a circuit containing series-connected loads equals the sum of the resistances of all loads.
  • The resistance in the circuit increases if loads are added in series and decreases if loads are removed.
  • The total resistance in a circuit containing parallel-connected loads is less than the smallest resistance value.
  • The total resistance decreases if loads are added in parallel and increases if loads are removed.
  • To calculate total resistance in a parallel circuit with three or more resistors, the formula for two resistors can be used by solving the problem for two resistors at a time.
  1. Calculate voltages at any point in a series or parallel circuit.
  • The total voltage applied across loads connected in series is divided across the individual loads.
  • Each load drops a set percentage of the applied voltage. The exact voltage drop across each load depends on the resistance of that load. The voltage drops across any two loads are the same if the resistance values are the same.
  • The voltage across each load is the same when loads are connected in parallel.
  • The voltage across each load remains the same if parallel loads are added or removed.
  1. Calculate current at any point in a series or parallel circuit.
  • The current in a circuit containing series-connected loads is the same throughout the circuit.
  • The current in the circuit will decrease if the circuit resistance increases and the current will increase if the circuit resistance decreases.
  • Total current in a circuit containing parallel-connected loads equals the sum of the current through all the loads.
  • Total current increases if loads are added in parallel and decrease if loads are removed.

Magnetism

  1. Define the molecular theory of magnetism and electromagnetism.
  • The molecular theory of magnetism is the theory that states that all substances are made up of an infinite number of molecular magnets that can be arranged in either an organized or disorganized manner.
  • Electromagnetism is the magnetism produced when an electric current passes through a conductor.
  • The direction in which current flows through a conductor determines the direction of the magnetic field around it. Lines of force (lines of induction) are present all along the full length of the conductor.
  • One line of force is called a Maxwell, and the total number of lines is called flux. The total number of lines of force in a space of 1 centimeter (cm) equals the flux density (in gauss) of the field. For example, 16 lines of force in 1 cm equal 16 gauss.
  • If a conductor is wound into multiple loops (a coil), the magnetic lines of force combine. Thus, the magnetic force of a coil with multiple turns is stronger than the magnetic force of a coil with a single loop.
  • Hans C. Oersted attempted several experiments to increase the strength of a magnetic field. He found three ways to increase the strength of a magnetic field in a coil: increase the amount of current by increasing the voltage, increase the number of turns in the coil, and insert an iron core through the coil.
  1. Define inductance and state how it affects an AC circuit.
  • Inductance (L) is the property of a circuit that causes it to oppose a change in current due to energy stored in a magnetic field.
  • In an inductive circuit, the current lags the voltage. When current and voltage are not synchronized, they are said to be out of phase with each other. The greater the inductance in a circuit, the larger the phase shift. In-phase AC sine waves occur in resistive circuits. Phase shifts in AC sine waves occur in inductive circuits.
  1. Define capacitance and state how it affects an AC circuit.
  • Capacitance (C) is the ability of a component or circuit to store energy in the form of an electrical charge.
  • A capacitor is an electric device that stores electrical energy by means of an electrostatic field. Small capacitors may be manufactured in several shapes and sizes for use in electronic control boards. Larger capacitors are manufactured for use in bigger devices like electrical motors.
  • A capacitor consists of two conducting surfaces separated by an insulating material called a dielectric. When a DC voltage is applied across two plates they will charge to a level corresponding to the difference of potential between the two terminals of the source. An electrostatic force is produced in the dielectric between the two plates. At this point, the capacitor is storing energy in the circuit.
  • When the charging voltage is removed and the shorting switch S2 is closed, the excess electrons on the left plate will move through the switch to the right plate. Now the capacitor acts as a voltage source with the left plate as the negative terminal and the right plate as the positive terminal. At this point, the capacitor is releasing energy into the circuit.
  • The motion of electrons will continue until there is no charge on either plate or the difference of potential is zero. At this point, all of the energy originally stored in the dielectric material will have been used to move the electrons from the left plate to the right plate. No electrostatic field exists between the plates at that time. When the capacitance is created in an electrical circuit, a phase shift occurs between the voltage and the current in the circuit.
  • In an AC circuit, the capacitor is constantly charging and discharging. The voltage across the capacitor is in constant opposition to the applied voltage. This constant opposition to changes in the applied voltage creates an opposition to current flow in the circuit. The amount of opposition offered to current flow in an AC circuit by a capacitor is a function of the capacitance and the frequency of the voltage.

Power

  1. Define true power and state its unit of measure and common abbreviation.
  • True power (PT) is the actual power used in an electrical circuit. True power is the power that is converted into work for use by devices, such as heating elements.
  • True power is measured in watts (W), kilowatts (kW), or megawatts (MW).
  • In DC circuits or AC circuits in which voltage and current are in phase, such as resistive loads, true power is equal to the voltage (E) times the current (I).
  1. Determine an unknown power, voltage, and current with the power formula.
  • The power formula is the relationship between power (P), voltage (E), and current (I) in an electrical circuit. Any value in this relationship may be found using the power formula when the other two values are known.
  • The power formula states that power (P) in a circuit is equal to voltage (E) times current (I).
  • The power formula states that voltage (E) in a circuit is equal to power (P) divided by current (I).
  • The power formula states that current (I) in a circuit is equal to power (P) divided by voltage (E).
  1. Calculate power at any point in a series or parallel circuit.
  • Power is produced when the voltage is applied to a load and current flows through the load.
  • The lower the resistance of the load or the higher the applied voltage, the more power is produced. The higher the resistance of the load or the lower the applied voltage, the less power is produced.
  • Total power produced in a series or parallel circuit is equal to the sum of the power produced by each load.
  1. Define reactive power and state its unit of measure and common abbreviation.
  • Reactive power is power absorbed and returned to a load due to its inductive and/or capacitive properties.
  • Reactive power is indicated by the letter Qand is measured in volt-amperes reactive (VAR).
  • Pure reactive power uses no true power. This is because pure reactive power performs no actual work, such as the production of heat. The reason reactive power does not work is because most of the reactive power drawn from a source is returned to that source.
  1. Define apparent power and state its unit of measure and common abbreviation.
  • Apparent power is a combination of true and reactive power.
  • Apparent power is the product of the voltage and current in a circuit calculated without considering the phase shift that may be present between the voltage and the current in a circuit.
  • Apparent power is expressed in volt-amperes (VA).
  • Apparent power is a measure of the system capacity. This is true because calculating apparent power considers all circuit current regardless of how it exists in the circuit.
  1. Define power factor and explain its relationship to efficiency.
  • Power factor (PF) is a ratio between true power and apparent power. True power is measured in watts (W) and apparent power is measured in volt-amperes (VA).

The nameplate information on a 1/4 HP inductive motor shows the difference between true power and apparent power. The 1/4 HP AC motor (resistive/reactive load) is required to lift a 60 lb load 30′ in 15 sec. To lift the load, the motor must deliver 186.5 W (true power). The motor nameplate lists motor current at 5 A and voltage at 115 V. The rated current (5 A) multiplied by the rated voltage (115 V) equals 575 VA.

  • An example of a power factor and efficiency can be shown with a small 60 Hz 1φ AC induction motor. The motor may be operated alone or a running capacitor can be added. When the motor is operated on its own, it has a lagging power factor of 37.5% efficiency. This is due to the effect of inductive reaction within the motor. When capacitors and capacitive reaction are introduced into the circuit, the current drawn by the motor drops 2.5 A. The drop in current draw results from the corrected power factor. This results in a less line voltage drop from the power source and a higher efficiency of the power source. The motor still uses 180 W of power to do its work but the overall efficiency of the system is significantly improved. The power factor was moved to 1.0 because of the balancing value of the running capacitor with the induction of the motor. Their opposing effects canceled each other out and left a 1.0 power factor.
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About Ahmad Faizan

Mr. Ahmed Faizan Sheikh, M.Sc. (USA), Research Fellow (USA), a member of IEEE & CIGRE, is a Fulbright Alumnus and earned his Master’s Degree in Electrical and Power Engineering from Kansas State University, USA.