Electrical Engineering Exam Questions

In a dielectric material, an electric charge is not free to move. It stays localized to the region where it was placed.

Magnetic field lines are continuous, unlike electric field lines that originate and terminate at charges.

Capacitance is a measure of a capacitor's ability to store electrical energy. For capacitors in series, the equivalent capacitance is always less than the smallest capacitance.

Field resistance refers to the resistance of the excitation circuit in DC motors, the circuit responsible for creating the magnetic field that interacts with the armature.

Chemical effects of AC are lower than DC because AC constantly changes direction, preventing significant buildup of charges for chemical reactions.

Diesel power plants require a constant power output for efficient operation. They can't easily be scaled down like other power plants, limiting their output to specific ranges.

The left-hand rule is used in electromagnetism. The thumb represents the direction of the force on a conductor, the index finger points in the magnetic field direction, and the middle finger represents the direction of the current.

Resistors in parallel have an equivalent resistance less than the smallest individual resistance. When resistors are connected in series, the equivalent resistance is the sum of individual resistances.

The rate at which a quantity grows exponentially over time, expressed as a percentage.

A type of electrical circuit where three resistors are connected in a 'Y' or 'star' shape, with the common point being the neutral.

A type of electrical circuit where three resistors are connected in a 'triangle' shape, forming a closed loop.

The brightness of a light source, measured in lux. It depends on the distance from the source.

A device used to measure the impurities in an insulating oil, which can affect its performance and longevity.

A type of insulator used in high voltage applications, designed to be suspended from a conductor.

The point in an AC circuit where the inductive and capacitive reactances cancel each other out, resulting in maximum current flowing through the circuit.

A 3-phase electrical system with four wires, where the neutral wire has a higher voltage than the phase wires due to an unbalanced load.

The ratio of average load to the maximum load. It is also known as the utilization factor.

The high-voltage winding of a transformer is placed closer to the core. This is due to the higher voltage and magnetic field strength. The low-voltage winding is placed farther away.

Series capacitors improve the steady-state stability of transmission lines by reducing the reactive power demand.

In the two-wattmeter method of power measurement, one wattmeter reading will be zero when the power factor is 0.5. This occurs because the voltage and current are in phase in one phase and exactly out of phase in another.

Mutual inductance (M) is the measure of how the magnetic field of one inductor influences the magnetic field of another inductor. When inductors are connected in series aiding, the magnetic fields add, increasing inductance. When in series opposing, the fields cancel, decreasing inductance.

The speed of an induction motor is determined by the slip (percentage of difference between synchronous speed and actual speed).

When resistors are connected in parallel, the total resistance is less than the smallest individual resistance. The formula is 1/Rtotal = 1/R1 + 1/R2 + ... + 1/Rn.

A reverse power relay is used to prevent motorizing of a generator. This occurs when a generator is connected to a bus, and the motor is running at a higher speed trying to drive the generator instead of the other way around.

The copper losses of a transformer are measured during a short circuit test where the secondary winding is shorted, and a low voltage is applied to the primary. This test allows for the measurement of the resistance of the windings, which is directly related to the copper losses.

The coefficient of coupling (k) represents the degree of magnetic coupling between two coils. It is calculated as the ratio of the mutual flux (Φ12) to the self-induced flux (Φ11) in one of the coils. In this case, k = Φ12 / Φ11 = 0.75 mWb / 0.50 mWb = 1.5. Since k cannot exceed 1, the coefficient of coupling is 0.6 (rounded to the nearest hundredth).

Peak envelope power (PEP) is the maximum power a transmitter can deliver in a single radio frequency (RF) cycle during a short period of time. For single-sideband (SSB) modulation, the PEP is calculated as (Vpeak-to-peak)^2 / (8 * R), where Vpeak-to-peak is the peak-to-peak voltage and R is the antenna resistance. In this case, PEP = (720V)^2 / (8 * 75 ohms) = 864W.

To improve the power factor of an inductive circuit, capacitors are connected in parallel. Capacitors draw leading reactive power, which cancels out the lagging reactive power drawn by inductive loads. The result is an overall improvement in the power factor, allowing for more efficient power usage.

High voltage transmission is used in grid systems for various reasons, but the primary purpose is to minimize line losses during bulk power transmission. The power loss in a transmission line is proportional to the square of the current. Using high voltage reduces the current required to transmit the same amount of power, resulting in lower line losses. This minimizes energy waste and improves overall efficiency.

Full duplex communication allows for simultaneous transmission and reception of information in both directions. This is achieved by using separate channels for transmitting and receiving signals, allowing for continuous communication without interruption.

The output voltage from a voltage divider is equal to the input voltage multiplied by the ratio of the resistor connected to the output terminal to the total resistance. In this case, the output voltage is 10% of the input, so the ratio of the output resistor to the total resistance is 0.1. Since the total resistance is 50 ohms, the output resistor value is 5 ohms. Therefore, the other resistor in the divider is 45 ohms.

The magnetic flux in a transformer is directly proportional to the applied voltage and inversely proportional to the frequency. To maintain the same magnetic flux in a transformer when switching from a 60 Hz to a 50 Hz system, the voltage must be adjusted. In this case, the new voltage should be 5/6 * 230V = 191.67V.

Zero-sequence current can flow from line to transformer banks when the connection involves a "Grounded Star/Delta" configuration.

The grease spot photometer is a tool used to compare light intensities from two sources. When the spot is moved closer to the standard light source, the illumination on both sides is equalized.

To make the illumination from the unknown light source twice that of the standard source, we need the inverse square law. The distance from the standard light source is inversely proportional to the light intensity.

If the illumination is equal when the spot is 25 cm from the standard light, we need to double that distance to halve the intensity.

The Gauss-Seidel method is a numerical technique specifically used to solve systems of linear algebraic equations.

Combined cycle power plants are designed to efficiently generate power for both baseload and peak load needs.

In a 15-bus system with 3 voltage-controlled buses, the size of the Jacobian matrix will be 25x25. The Jacobian matrix is a critical component used in load flow studies, which analyzes the performance of a power system.

Generally, the Newton-Raphson method for solving power systems requires fewer iterations compared to the Gauss-Seidel method, but each iteration takes longer. The Newton-Raphson method converges faster, but each step involves more complex calculations.

Circuit breakers are rated based on their ability to handle symmetrical faults. This refers to fault currents that are ideally balanced between the phases and are often the worst-case scenario for electrical systems.

The total resistance of a series-parallel combination of resistors is found by combining the individual resistances using the appropriate formulas A. For series, the total resistance is the sum of individual resistances. B. For parallel, the total resistance is the reciprocal of the sum of reciprocals of individual resistances.