Electrical Engineering Concepts Quiz

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Questions and Answers

What is the slip of a 400 V, 3-phase, 4-pole induction motor when rotating at 1440 rpm?

The slip is approximately 4%.

In a three-phase star connected system, what is the relationship between phase and line voltage?

The line voltage is √3 times the phase voltage.

When a pure inductance is connected to an alternating current source, how does the voltage relate to the current?

The voltage leads the current by 90 degrees.

What is the Q factor of a series circuit consisting of R = 10 ohms, L = 0.1 H, and C = 10 µF?

The Q factor is 100. Signup and view all the answers

If a parallel circuit is shunted by a resistance, how is the Q factor affected?

The Q factor is decreased. Signup and view all the answers

What is the nature of a circuit if the current lags the voltage by 60 degrees?

The circuit is an RL circuit. Signup and view all the answers

What voltage leads the other if E1 = Asin(wt) and E2 = Asin(wt - P)?

E1 leads E2. Signup and view all the answers

What is the power consumed by a pure capacitance connected to an AC source?

The power consumed is zero. Signup and view all the answers

In a balanced three-phase 4-wire system with a current of 10 A in each phase, what is the current through the neutral wire?

0 A Signup and view all the answers

Calculate the inductive reactance of a coil with an inductance of 0.2 H at a frequency of 50 Hz.

62.8 ohms Signup and view all the answers

How many degrees apart are the emfs in a three-phase system?

120˚ apart Signup and view all the answers

What role does the commutator play in a D.C. machine?

Acts as a full-wave rectifier Signup and view all the answers

What material can be used to reduce hysteresis loss in a transformer?

Silicon Steel Core Signup and view all the answers

What type of rotor does a three-phase slip-ring induction motor have?

Wound rotor Signup and view all the answers

In a DC shunt motor, how can the direction of rotation be reversed?

By interchanging the supply terminals Signup and view all the answers

What is the form factor of a sinusoidal wave?

Always equals to 1.11 Signup and view all the answers

What is the power factor of a purely inductive circuit?

Zero Signup and view all the answers

In which scenario is the superposition theorem not valid?

Power responses Signup and view all the answers

What is the total instantaneous power supplied by a balanced R-L load in a 3-phase AC supply?

Typically, it is expressed as $P = rac{3}{ oot{I^2 R}}$ Signup and view all the answers

In an RL series circuit, how does the voltage across the inductor relate to the voltage across the resistor?

VL lags VR by 90 degrees. Signup and view all the answers

At what angle does the RMS value of a sinusoidal AC current equal its peak value?

90 degrees Signup and view all the answers

What is the characteristics of an ideal current source?

No resistance Signup and view all the answers

How does the excitation current of a transformer typically compare to the full load current?

Around 2% of full load current Signup and view all the answers

What happens to the power factor at resonance in a series R-L-C circuit?

It becomes unity. Signup and view all the answers

In a 3-phase system, how are the phase voltages related in terms of their angular displacement?

The phase voltages are 120° apart. Signup and view all the answers

What is the effect of increasing frequency in an a.c. circuit with R, L, and C in series operating on a lagging power factor?

Increasing frequency will reduce the current. Signup and view all the answers

What does KCL signify in terms of electrical circuits?

KCL is a consequence of the law of conservation of charge. Signup and view all the answers

Why is the armature of a D.C. machine laminated?

The armature is laminated to reduce eddy current losses. Signup and view all the answers

What happens if the supply terminals of a D.C. shunt motor are interchanged?

The direction of rotation will reverse. Signup and view all the answers

What is the magnetic force experienced by a current-carrying conductor in a magnetic field at an angle?

The force is given by $BIl , sin , \theta$. Signup and view all the answers

In an electrical circuit, what does the term 'fusing factor' refer to?

The fusing factor is the ratio of the current required to melt a fuse to the rated current of the fuse. Signup and view all the answers

What distinguishes MCCB from MCB in electrical systems?

MCCB has a higher current rating than MCB and is suitable for medium voltage applications. Signup and view all the answers

What is the shape of a current waveform with a form factor of 1?

A sine wave. Signup and view all the answers

What do you control by using a starter in a DC motor during starting?

The starting current. Signup and view all the answers

What principle does the superposition theorem satisfy?

The principle of linearity. Signup and view all the answers

What is the relationship between the input and output voltage of a Buck converter and Boost converter?

A Buck converter steps down voltage, while a Boost converter steps up voltage. Signup and view all the answers

Which alternating current lags the other in L1 = sin(wt – 30) and L2=sin(wt +30) and by what angle?

L2 lags L1 by 60 degrees. Signup and view all the answers

When does maximum efficiency of a transformer occur?

When the load corresponds to the rated capacity. Signup and view all the answers

What is the phase relationship between the primary and secondary voltages of a transformer?

The primary and secondary voltages are in phase. Signup and view all the answers

What does the area of a hysteresis loop measure?

Energy loss due to magnetic hysteresis. Signup and view all the answers

What is the principle of a Miniature Circuit Breaker (MCB)?

The principle of an MCB is to automatically switch off the electrical circuit when it detects an overload or a fault, ensuring safety. Signup and view all the answers

What does RCCB stand for?

RCCB stands for Residual Current Circuit Breaker. Signup and view all the answers

How is earth resistance measured?

Earth resistance is measured using an earth resistance tester or by the fall-of-potential method. Signup and view all the answers

What is the difference between the EMF and potential difference (PD) of a cell?

EMF is the total energy supplied by the cell per unit charge, while PD is the energy used per unit charge in the circuit. Signup and view all the answers

How does adding a small capacitance to a highly inductive circuit affect the power factor?

Adding a small capacitance will increase the power factor of the circuit. Signup and view all the answers

In a pure inductive circuit, how much actual power is consumed?

In a pure inductive circuit, the actual power consumed is zero. Signup and view all the answers

What happens to current in a purely inductive circuit if the supply frequency is reduced to half?

The current in a purely inductive circuit will double if the supply frequency is reduced to half. Signup and view all the answers

What characterizes a current as alternating (AC)?

A current is characterized as alternating when its magnitude and direction change periodically over time. Signup and view all the answers

Study Notes

Basic Electrical Engineering - 1 Mark Questions

Fuses: Protective devices that melt when excessive current flows, opening the circuit.
Power Transfer Efficiency: Maximum when the load's impedance matches the source's impedance.
RLC Circuit Resonance: Occurs when the inductive and capacitive reactances are equal.
Core Type Transformer: A transformer with a core made up of multiple laminations to reduce eddy current losses.
Alternator/DC Generator Principles: Alternators generate AC via electromagnetic induction, while DC generators produce DC using a commutator.
Duty Cycle: The fraction of time during a period that a signal is active.
Transformer Function: Transfers electrical energy between circuits with different voltage levels.
Synchronous Speed: The rotational speed of a synchronous machine, related to frequency and number of poles.
Inverter Classification: Various types like voltage source inverters and current source inverters.
Secondary Cell: A rechargeable cell, like a battery.
Coil Impedance: Calculated using Pythagorean theorem from resistance and inductive reactance.
Transformer Copper Loss: At half-load, the copper loss is one-quarter of the full-load copper loss.
Form Factor: Ratio of RMS value to average value of a waveform.
AC Circuit Significane of Form Factor: A quantitative measure of how much a waveform deviates from a pure sine wave.
Shell Type Transformer: A transformer with a core that surrounds the windings.
Transformer Regulation: The change in voltage between no-load and full-load conditions.
Transformer Efficiency: Ratio of output power to input power, expressed as a percentage.
Iron Losses: Constant losses in transformers due to eddy currents and hysteresis.
Copper Losses: Variable losses in transformers depending on load current and resistance.
Half Power Frequency: Frequency at which output power is half its maximum value.
Active Power in Pure Components:
- Resistor: P = V^2/R
- Inductor: P = 0
- Capacitor: P = 0
Single-Phase Transformer EMF Equation: Specifies the relationship between voltage and flux in single-phase transformers.
RLC Circuit Bandwidth: The range of frequencies over which the circuit has a certain level of response.
Laminated Transformer Cores: Reduce eddy current losses by minimizing current paths.
Power Factor in Resistive Circuit: 1
RLC Series Resonance Current: Maximum
Equivalent Impedance of Parallel Components: Calculated by impedance reciprocal addition.
DC Motor Direction: Determined by Fleming's left-hand rule.
Commercial Electricity Unit: One kilowatt-hour (kWh).
DC to DC Converter Output Voltage: Proportional to the on-time (Ton).
Ground Insulation Resistance: Sufficiently low to ensure safety.

Further Topics (Page 2)

Form Factor Definition: Ratios of RMS to average value of a waveform.
DC to AC Converter: A device that converts DC to AC.
Power Triangle: Graphical representation of active, reactive, and apparent power in AC circuits.
Converter/Inverter Definition: Devices to convert between DC and AC.
DC Motor Starting Considerations: Requires a starter to limit inrush current.
Superposition Theorem Applicability: Only applicable to linear circuits.
Hysteresis Loop Area: Measure of energy loss in a magnetic material.
AC Circuit Resistance: Impedance's real component.
Transformer Voltage Phase Relationship: Primary and secondary voltages are in-phase or out-of-phase by 180 degrees.
Induction Motor Slip: The difference between synchronous speed and actual speed.
Power Calculation from Phase Voltage and Current: Use of proper formulas based on connection of a transformer (delta-delta, delta-star, star-star).

Further Topics (Page 3)

Sinusoidal Voltage Parameters: Includes RMS value, frequency, and phase.
Three-Phase Induction Motor Supply: Three-phase AC applied to the stator windings only.
Induction Motor Slip Relationship: Relates synchronous speed, actual speed, and slip percentage.
Three-Phase Star/Delta Relationships: Relationships between line and phase voltages and currents.
AC Circuit Voltage and Current Relationship in Inductance: Voltage leads current by 90 degrees.
AC Parallel Circuit Resonance: Describes the behavior of a parallel circuit at various frequencies, including the resonant frequency.
Q-factor of Series Circuit: Relationship between resistance, inductance, and capacitance in a series resonant circuit.
Electrical Circuit Energy Storage: Includes formulas for energy in inductors and capacitors.

Further Topics (Page 4)

DC Machine Commutator Function: Acts as a rectifier.
Transformer Core Material Selection: Minimizes hysteresis and eddy-current losses.
Three-Phase Induction Motor Rotor Types: Includes wound rotor and squirrel-cage rotor.
DC Machine Direction of Rotation Change: By reversing supply connections.
Electrical Permittivity: Constant associated with a medium's ability to store electric field energy.
Three-Phase 4-wire System Neutral Current: In balanced conditions, neutral current is zero.
Superposition Theorem Limitations: Applies only to linear circuits.
Transformer Principle: Energy transformation via mutual induction.
Direct Current Generator Synchronous Speed Determination: Related to the frequency and number of poles.

Further Topics (Page 5 & 6)

Excitation Current in Transformers: Relatively small compared to full-load current.
RLC Circuit Power Factor at Resonance: Unity.
Transformer Efficiency Maximization: Equalizing copper losses and iron losses.
EMF Direction in DC Generators: Determined by Fleming's Right-hand rule.
DC Motor Rotor Winding: Uses either lap or wave winding to connect in a loop.
AC Circuit Power Calculation: Includes Formulas for various types.
KVL & KCL Usage: Used in circuit analysis to relate voltages and currents.
Hysteresis and Eddy Current Losses: Minimize energy loss by using laminated core.
AC Circuit Response at Different Frequencies: Describes the behavior of circuits at different frequencies, including resonance.
Three Phase System Phase Relation: Relationship between phase and line voltages.

Further Topics (Page 7)

Transformer No-Load Current: Small current drawn from the supply even at no load.
Transformer Efficiency: Measure of energy conversion efficiency of a transformer.
Transformer Ratings: Usually quantified in kVA due to load being a factor of both current and voltage.
Transformer All-Day Efficiency: Considered for usage over extended time periods.
Transformer Losses: Losses associated with transformer operation.
Transformer Temperature Considerations: Affects the operation of the transformer.

Further Topics (Page 8)

Transformer Formulas: Specifics like voltage ratio and turn ratio.
Transformer Losses: Types of losses incurred by transformers during usage.
Transformer Regulation: Calculations of voltage regulation value at different loads.

Further Topics (Page 9)

Synchronous Generator Speed and Frequency: Dependence of speed on frequency.
Damper Winding: Used to manage oscillations and hunting.
Synchronous Compensator: Used in power systems to adjust voltage and power flow.
Switching and Duty Cycle in Choppers: Details on the usage, operation, and formulas related to inverters.

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Description

Test your knowledge on key concepts in electrical engineering, including induction motors, AC circuits, and Q factors. This quiz covers various theoretical and practical aspects such as slip of motors, phase relationships in systems, and current-voltage relationships in inductive and capacitive circuits.