Basic Electrical Flashcards

In an AC circuit, which of the following accurately depicts the average value?

Answer: RMS value/Form factor

In an AC circuit, the form factor is defined as the ratio of the RMS (Root Mean Square) value to the average value of a waveform. Therefore, to find the average value, you can rearrange this relationship: Average Value = RMS Value / Form Factor. This formula allows for the calculation of the average value when the RMS value and form factor are known.

Who developed an approach to measure current and defined electric current?

Answer: Andre-Marie Ampere

André-Marie Ampère was a pioneering French physicist and mathematician who made fundamental contributions to the understanding of electromagnetism. He developed the theory of electrodynamics and formulated Ampère's law, which describes the relationship between electric current and the magnetic field it produces. The unit of electric current, the ampere, is named in his honor.

How many electrons are required to produce a 2 Coulomb electric charge?

Answer: 12.48 * 1018 electrons

The charge of a single electron is approximately 1.602 x 10^-19 Coulombs. To determine the number of electrons required to produce a 2 Coulomb electric charge, you divide the total charge by the charge of one electron. Calculation: 2 C / (1.602 x 10^-19 C/electron) ≈ 1.248 x 10^19 electrons, which can also be written as 12.48 x 10^18 electrons.

Which of the following statements regarding direct current is true?

Answer: Can be transported to larger distances with less loss in power

While conventional DC transmission has higher losses over long distances compared to AC, High-Voltage Direct Current (HVDC) transmission systems are specifically designed to transport power over very long distances with significantly less loss than equivalent AC systems. HVDC is particularly advantageous for submarine cables and long-haul overhead lines, making this statement true in the context of modern power transmission technologies.

Who was the first person to experience the power of magnetism?

Answer: Hans Christian Orsted

Hans Christian Ørsted, a Danish physicist, made the groundbreaking discovery in 1820 that electric currents produce magnetic fields. He observed that a compass needle deflected when placed near a wire carrying an electric current, demonstrating the fundamental connection between electricity and magnetism and laying the foundation for electromagnetism.

Which of the following statements regarding electrical conductivity is true? Which of the following statements regarding electrical conductivity is true?

Answer: It is the ratio of current density to the electric field

Electrical conductivity (σ) is a material property that quantifies its ability to conduct electric current. It is defined as the ratio of the current density (J), which is the current per unit cross-sectional area, to the electric field (E) that drives the current. This relationship is expressed by the equation J = σE, a microscopic form of Ohm's Law.

What is the cause of the current's flow?

Answer: Electrons

Electric current is fundamentally the flow of electric charge. In most common conductors, such as metals, the charge carriers are free electrons. These electrons are not tightly bound to individual atoms and can move freely through the material under the influence of an electric field, thus constituting the electric current.

Which of the following must be zero according to KCL?

Answer: Algebraic sum of currents entering and leaving a junction

Kirchhoff's Current Law (KCL) is a fundamental principle in circuit analysis, stating that the algebraic sum of all currents entering and leaving any junction (or node) in an electrical circuit must be zero. This law is a direct application of the principle of conservation of electric charge, meaning that charge cannot accumulate at a node.

How many possible directions may the electric field have at one location?

Answer: One

The electric field at any given location in space is a vector quantity, meaning it has both magnitude and a specific direction. For a particular point, the net electric field resulting from all surrounding charges will always point in a single, unique direction, indicating the force that a positive test charge would experience at that exact spot.

When there are more secondary turns than main turns in a transformer, which of the following will happen?

Answer: The voltage gets stepped up

In a transformer, the voltage transformation is directly proportional to the turns ratio. If the number of turns in the secondary winding is greater than the number of turns in the primary winding (Ns > Np), the transformer is designed to step up the voltage. This means the output voltage across the secondary coil will be higher than the input voltage across the primary coil.

Which of the following statements regarding electrical engineering's voltage transformation ratio is true?

Answer: Ratio of induced emf in secondary to induced emf in primary

The voltage transformation ratio (or turns ratio) of a transformer is defined as the ratio of the induced electromotive force (emf) in the secondary winding to the induced emf in the primary winding. This ratio is approximately equal to the ratio of the number of turns in the secondary coil to the number of turns in the primary coil, and it dictates how voltage is stepped up or down.

Which of the following statements regarding the induced emf in the transformer primary is true according to electrical engineering fundamentals?

Answer: It is the product of primary turns and emf induced per turn

The total induced electromotive force (emf) in the primary winding of a transformer is directly proportional to the number of turns in that winding. Each turn contributes an equal amount of induced emf. Therefore, the total primary induced emf is calculated by multiplying the number of primary turns by the emf induced per single turn.

When the secondary is open, which of the following currents is drawn by the primary circuit of an ideal transformer?

Answer: Magnetizing current

When the secondary winding of an ideal transformer is open-circuited, no load current flows through it. However, the primary winding still draws a small current from the supply, known as the magnetizing current. This current is responsible for establishing and maintaining the alternating magnetic flux in the transformer's core, which is essential for its operation.

What does an electrical element's positive power mean?

Answer: Element is absorbing power

In electrical engineering, the convention for power is that a positive value indicates that an element is absorbing or consuming power from the circuit. Conversely, if an element is supplying or generating power, its power value would be considered negative. This convention helps in analyzing power flow within a circuit.

How does the supply voltage affect a DC motor's response to an induce emf?

Answer: It will oppose the supply voltage

When a DC motor's armature rotates within a magnetic field, it induces an electromotive force (emf) known as back emf. According to Lenz's Law, this induced back emf always acts in a direction that opposes the applied supply voltage. This opposition is crucial as it limits the armature current and helps regulate the motor's speed.

Which of the following electrical engineering circuit types cannot be examined using Ohm's law?

Answer: Unilateral

Ohm's law describes a linear relationship between voltage and current (V=IR), implying a constant resistance regardless of current direction. Unilateral circuits, such as those containing diodes or transistors, exhibit non-linear and direction-dependent characteristics, meaning their V-I relationship cannot be accurately described by a single, constant resistance value as implied by Ohm's law. Therefore, Ohm's law is not universally applicable to unilateral circuits.