Dgca Module 03 Electrical Fundamentals Question

Generator brushes are typically made of carbon. Carbon brushes are commonly used in generators because they have good electrical conductivity and can withstand high temperatures. They also have a low coefficient of friction, which helps to reduce wear and tear on the commutator. Additionally, carbon brushes are self-lubricating, which helps to prevent overheating and prolong the lifespan of the brushes.

The 4th band on a resistor represents the tolerance. Tolerance refers to the allowable deviation from the resistor's stated resistance value. It indicates the range within which the actual resistance of the resistor can vary. This is important because resistors are not manufactured with 100% accuracy, and the tolerance value helps ensure that the resistor falls within an acceptable range of resistance.

The unit of power is Joule/sec because power is defined as the rate at which work is done or energy is transferred. The Joule is the unit of energy, and since power is the amount of energy transferred per unit time, the unit of power is Joule/sec.

An ideal transformer is a theoretical concept that assumes no losses in the transformer. In an ideal transformer, the input power is equal to the output power, and there are no losses due to resistance, leakage, or hysteresis. This means that the transformer operates at 100% efficiency, converting electrical energy from one voltage level to another without any energy losses. Therefore, an ideal transformer can be considered as a transformer with no loss.

Faraday's Law states that the magnitude of the electromotive force (EMF) induced in a circuit is directly proportional to the rate of change of magnetic flux through the circuit. This means that as the magnetic flux through a circuit changes, an EMF is induced in the circuit. The greater the rate of change of flux, the greater the magnitude of the induced EMF. Therefore, the correct answer is that the magnitude of EMF is directly proportional to the rate of change of flux.

Reluctance is the correct answer because it refers to the opposition that a material exhibits to the flow of magnetic flux. It is similar to resistance in an electrical circuit, where it hinders the flow of current. Permeability, on the other hand, is a measure of how easily a material can be magnetized, while resistance is the opposition to the flow of electric current. Therefore, reluctance is the most appropriate term to describe opposition to a magnetic field.

The mass of an atom is mainly contained in the nucleus. The nucleus is the central part of an atom that contains protons and neutrons. Protons have a positive charge, while neutrons have no charge. Together, protons and neutrons contribute to the mass of the atom. Electrons, on the other hand, are much smaller in mass and are found in the electron cloud surrounding the nucleus. Therefore, the correct answer is the nucleus.

A solar cell is an example of a light source because it converts sunlight directly into electricity. Solar cells are made up of semiconductor materials that absorb photons from sunlight and release electrons, generating an electric current. This process is known as the photovoltaic effect. Therefore, the correct answer is light.

To calculate the generator output, you need to know the armature speed and field strength. The armature speed refers to the rotational speed of the armature, which determines the frequency of the generated electricity. The field strength refers to the strength of the magnetic field created by the field windings, which determines the voltage of the generated electricity. By knowing both the armature speed and field strength, you can accurately calculate the generator output.

The time constant of an inductor is given by L/R, where L is the inductance and R is the resistance. This formula represents the time it takes for the current in the inductor to reach approximately 63.2% of its final value when a voltage is applied. A larger inductance or a smaller resistance will result in a longer time constant, indicating a slower rate of change in current.

A low pass filter allows signals with a frequency lower than a certain cut-off frequency to pass through while attenuating or blocking higher frequency signals. This means that it lets low frequency signals pass through while reducing the amplitude of high frequency signals. Therefore, a low pass filter is used to pass low frequency signals but attenuates higher frequency signals.

The capacitance is directly proportional to the plate surface area. This means that as the plate surface area increases, the capacitance also increases. This relationship can be explained by the fact that a larger surface area allows for more electric field lines to pass through the capacitor, resulting in a greater charge storage capacity. Conversely, if the plate surface area decreases, the capacitance will also decrease.

When cells are connected in series, the voltage across each cell adds up to give the total voltage. This is because the positive terminal of one cell is connected to the negative terminal of the next cell, creating a continuous path for the flow of electrons. As a result, the voltages of the individual cells add up, resulting in an additive effect.

An atom with less than 4 electrons in its outer shell has low electrical resistance. This is because atoms with less than 4 electrons in their outer shell are more likely to lose or gain electrons to achieve a stable electron configuration. This process of gaining or losing electrons allows the atom to become electrically charged, making it easier for electric current to flow through it. Therefore, atoms with less than 4 electrons in their outer shell have low electrical resistance.

The motor is spinning at 50 cycles per second, which means it completes 50 cycles in 1 second. To find the length of 1 cycle, we divide 1 second by 50 cycles. This gives us 0.02 seconds, which is the correct answer.

A commutator is used to convert the alternating current induced in the loops of the rotating armature of a DC generator into direct current as it leaves the generator. The commutator consists of a set of copper segments that are connected to the armature coils. As the armature rotates, the commutator reverses the direction of the current flow in the coils, ensuring that the current always flows in the same direction in the external circuit. This process converts the alternating current into direct current.

Resistance is independent of the mass of the conductor because resistance is determined by the material and dimensions of the conductor, not its mass. The mass of the conductor does not affect the flow of electrons through it or the collisions that occur between the electrons and the atoms of the conductor, which are the factors that determine resistance. Therefore, changing the mass of the conductor will not alter its resistance.

When an induced current is generated in a coil, it creates a magnetic field that opposes the change in magnetic flux that is causing the current. This is known as Lenz's law. According to Faraday's law of electromagnetic induction, the induced EMF is directly proportional to the rate of change of magnetic flux. Therefore, the induced current opposes the EMF producing it in order to maintain the equilibrium and conserve energy.

The method most often used in overcoming the effect of armature reaction is through the use of interpoles. Interpoles are small auxiliary poles placed between the main field poles of a DC machine. They are connected in series with the armature winding and have the opposite polarity to the main field poles. By producing a magnetic field that counteracts the armature reaction, interpoles help to reduce the distortion of the main magnetic field and minimize the impact on the commutation process. This improves the overall performance and efficiency of the machine.

In a thermistor, which is a type of temperature sensor, the resistance decreases as the temperature increases. This is because the thermistor is made of a material whose resistance decreases with increasing temperature. As the temperature rises, the atoms in the material vibrate more vigorously, causing more free electrons to move through the material, resulting in a decrease in resistance.

The principal advantage of a series-wound DC motor is its high starting torque. This means that it can easily start heavy loads or overcome initial resistance. The series-wound DC motor is designed in such a way that the field winding and armature winding are connected in series, allowing the current to flow through both windings. This configuration results in a high starting torque, making it suitable for applications where a lot of power is needed to start the motor, such as in electric vehicles or industrial machinery.

The correct answer is "Both 1 and 2 are true". This means that both statements 1 and 2 are true. Statement 1 states that when inductance is more, there are more flux lines. This is true because inductance is directly proportional to the number of flux lines. Statement 2 states that when inductance is less, there are less flux lines. This is also true because inductance is inversely proportional to the number of flux lines. Therefore, both statements 1 and 2 are true.

A material with low permeability refers to its ability to resist the formation of magnetic fields within itself when subjected to an external magnetic field. Diamagnetic materials exhibit this property as they have a weak and negative magnetic susceptibility, causing them to create an opposing magnetic field when exposed to a magnetic field. This results in the material being repelled by the magnetic field. In contrast, paramagnetic and ferromagnetic materials have higher permeability and are attracted to magnetic fields.

When elements such as phosphorus, which have 5 electrons in their outer shell, combine with pure silicon, they act as donor atoms. This is because phosphorus has one extra electron that it can easily give away to the silicon atoms. This extra electron creates a negative charge, making the combined material n-type semiconductor. Therefore, the correct answer is "donor."

To change the direction of rotation of a DC electric motor, one can reverse the electrical connections to either the field or armature windings. By doing so, the polarity of the magnetic field generated by the windings is reversed, causing the motor to rotate in the opposite direction. This can be achieved by swapping the positive and negative terminals of the windings, effectively reversing the flow of current through them.

The windings embedded in the pole faces of a DC generator are compensating windings. These windings are placed in the pole faces to reduce the effects of armature reaction, which is the distortion of the magnetic field due to the current flowing in the armature. By using compensating windings, the generator can maintain a more stable voltage output by counteracting the armature reaction. This helps to improve the overall performance and efficiency of the generator.

When two inductive coils are placed in close proximity with each other at 90 degrees, there is no flux linkage between them. This is because the magnetic field produced by one coil is perpendicular to the other coil, resulting in no magnetic coupling between them. Therefore, the number of flux linkages is zero.

Retentively is the correct answer because it refers to the ability of a magnet to retain its magnetism over time. It explains the property of the magnet holding some of its magnetism. Reluctance refers to the opposition of a material to magnetic flux, and permittivity refers to the ability of a material to store electrical energy in an electric field.

The correct answer is "few turns of thick wire." In a series wound DC motor, the field winding is connected in series with the armature winding. This type of motor requires a strong magnetic field to generate high torque. The field winding is made up of a few turns of thick wire to provide a low resistance path for the current to flow through. This allows a large current to flow through the field winding, creating a strong magnetic field.

The correct answer is "Both." Both permittivity and coercivity are properties associated with magnetism. Permittivity refers to the ability of a material to store electrical energy in an electric field, while coercivity is the measure of a material's resistance to becoming demagnetized. Both properties are important in understanding and manipulating magnetic fields and materials.

When the generator speed is halved, it means that the rotor is rotating at a slower rate. However, since the field strength is doubled, it compensates for the decrease in speed and maintains the same voltage output. This is because the field strength determines the strength of the magnetic field, which in turn affects the voltage output. Therefore, when the field strength is doubled, it counteracts the decrease in speed and keeps the voltage output unchanged.

In a shunt motor, reversing both the field current and the armature current will not affect the direction of the motor. This is because the field current creates a magnetic field that interacts with the armature current to produce motion. Reversing both currents will simply reverse the magnetic field, but the interaction between the two currents will still result in the motor running in the same direction.

The time constant in an inductive circuit is the time required for the current to reach 63.2% of its maximum value. This value is derived from the exponential decay equation that describes the behavior of current in an inductive circuit. At the time constant, the current has reached approximately 63.2% of its maximum value.

To maintain a constant voltage output from an aircraft generator, the strength of the magnetic field needs to be varied. This is because the voltage output of a generator is directly proportional to the strength of the magnetic field. By adjusting the strength of the magnetic field, the generator can compensate for changes in speed and load, ensuring a constant voltage output. Varying the speed at which the armature rotates or the number of conductors in the armature would not be effective in maintaining a constant voltage output.

Interpole windings are fitted in series with the armature in DC series wound generators. This is because interpole windings are used to provide a magnetic field that opposes the armature reaction, which helps in reducing the commutation problems in the generator. By placing the interpole windings in series with the armature, the magnetic field produced by the armature current is counteracted, ensuring smooth and efficient operation of the generator.

When inductors are connected in parallel, the total inductance is less than the inductance of the lowest rated inductor. This is because inductors in parallel create multiple paths for the current to flow, which reduces the overall inductance. The inductors effectively "share" the current, resulting in a decrease in the total inductance compared to the individual inductances.

When an electron leaves a hole, a photon is radiated in an LED (Light Emitting Diode). LEDs are semiconductor devices that emit light when an electric current is applied to them. The movement of electrons within the LED creates a recombination process where an electron fills a hole, releasing energy in the form of a photon. Therefore, an LED is the equipment in which a photon is radiated when an electron leaves a hole.

The total inductance of inductors connected in parallel can be found by using the formula: 1/Ltotal = 1/L1 + 1/L2 + 1/L3 + ... In this case, the given inductors are 10 mH, 5 mH, and 20 mH. Plugging these values into the formula, we get 1/Ltotal = 1/10 + 1/5 + 1/20. Simplifying this equation gives us 1/Ltotal = 4/20 + 8/20 + 1/20 = 13/20. Taking the reciprocal of both sides, we find that Ltotal = 20/13 mH, which is approximately equal to 2.86 mH. Therefore, the correct answer is 2.86 mH.

Aircraft engine starter motors are generally of the series type. In a series motor, the field coils and armature are connected in series, meaning that the current flows through both the field coils and armature in a single path. This type of motor provides high starting torque, which is necessary for starting large engines. Additionally, series motors have a simple design and are able to operate at high speeds.

When an inductor is saturated, it means that it has reached its maximum magnetic flux density. This occurs when the inductor is exposed to a magnetic field that is too strong, causing the core material to become fully magnetized. At this point, the inductor cannot accept any more lines of flux and its magnetic properties become compromised. This can lead to distortion and loss of inductance, affecting the performance of the inductor in a circuit.

Some electric motors have two sets of field windings wound in opposite directions so that the motor can be operated in either direction. This is because the direction of rotation of an electric motor is determined by the direction of the magnetic field produced by the field windings. By having two sets of field windings wound in opposite directions, the motor can be easily switched to operate in either direction by changing the direction of the current flowing through the windings. This provides flexibility and allows the motor to be used for various applications where the direction of rotation needs to be controlled.

The interpole windings carry the same current as the armature. Interpole windings are a type of winding used in DC generators to improve commutation. They are placed between the main field poles and are connected in series with the armature. The purpose of the interpoles is to produce a magnetic field that opposes the armature reaction, thus reducing the effect of armature reaction on commutation. To achieve this, the interpoles must carry the same current as the armature, allowing them to generate a magnetic field that counteracts the armature reaction.

Generators are rated based on their power output, which is measured in watts. The rating indicates the maximum amount of power that the generator can provide at its rated voltage. This is an important specification as it helps determine the generator's capacity and suitability for various applications.

Interpoles in a generator are used to overcome armature reaction and reduce arcing at the brushes. They are not used to reduce field strength. The field strength is controlled by the excitation current supplied to the generator.

Reactive power is represented by IVsinɸ. This is because reactive power is the component of power in an AC circuit that is not converted into useful work, but rather oscillates between the source and the load. It is measured in volt-amps reactive (VAR) and is calculated by multiplying the current (I) and the voltage (V) by the sine of the phase angle (ɸ) between them.

When a circuit has 28 volts applied and the current flowing through a 2 ohms resistance is 1 amp, it means that the total resistance in the circuit is 2 ohms. Since the other resistor is in series with the 2 ohm resistor, it means that the total resistance of the circuit is the sum of the resistances of both resistors, which is 26 ohms + 2 ohms = 28 ohms. Therefore, the correct answer is 26 ohm in series with 2 ohm resistor.

In a DC motor, the stator's magnetic field moves in the opposite direction of rotation of the armature due to armature reaction. This is because the armature reaction causes a magnetic field to be produced in the stator, which interacts with the permanent magnets or field windings in the rotor. This interaction causes the stator's magnetic field to move in the opposite direction of the armature's rotation, resulting in the generation of torque and the rotation of the motor.

Decreasing the field current in a shunt motor will increase the speed and increase the torque. In a shunt motor, the field current is responsible for creating the magnetic field that interacts with the armature current to produce torque. By decreasing the field current, the strength of the magnetic field decreases, resulting in a weaker interaction with the armature current. This causes the motor to spin faster (increase speed) as there is less resistance from the magnetic field. However, the decrease in the magnetic field also reduces the torque produced by the motor, meaning it has less force to overcome resistance or perform work. Therefore, the speed and torque both increase when the field current is decreased.

Armature reaction refers to the effect of the magnetic field produced by the armature current on the main magnetic field in a generator. This interaction between the two magnetic fields causes a force to be exerted on the armature, resulting in its movement. In this case, the armature reaction causes the MNA (Main North Armature) to move in the direction of rotation.