I85PREP
⌘ K
TP EIMSA study materials
TP EIMSA study resources

TP EIMSA practice questions

One question at a time. Build your TP EIMSA understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Electrical Safety and Standards

Under IEC 60479-1, which physiological effect is associated with the threshold of ventricular fibrillation for a current path through the human body?

  1. The threshold at which cardiac muscle loses coordinated contraction and fibrillation may begin Correct answer.
  2. The let-go threshold where the person can no longer release a gripped conductor
  3. The threshold at which involuntary muscular contraction becomes visible
  4. The perception threshold at which a faint tingling is first felt

Explanation

Ventricular fibrillation is the loss of coordinated cardiac contraction caused by current passing through the heart region, and IEC 60479-1 defines its threshold as a function of current magnitude and duration. It is a distinct effect from perception, let-go, and visible muscle contraction, which occur at lower current values.

Question 2Electrical Safety and Standards

In a TN-S earthing system, how are the protective conductor and the neutral conductor arranged?

  1. They are separate conductors from the supply source to the installation Correct answer.
  2. The protective conductor is connected to a local earth electrode only
  3. The neutral is earthed only at the load end of the installation
  4. They are combined in a single PEN conductor throughout the installation

Explanation

TN-S means the neutral and protective functions are carried by separate conductors over the whole system, from the source to the point of use. This differs from TN-C, where they are combined in a PEN conductor, and from TT, where the installation has its own local earth electrode.

Question 3Electrical Safety and Standards

What is the primary function of a residual current device (RCD) in an electrical installation?

  1. To limit fault current magnitude by inserting impedance in the circuit
  2. To protect motors against sustained overload by thermal tripping
  3. To isolate the installation for maintenance by manual operation
  4. To detect imbalance between live and neutral currents and disconnect the supply Correct answer.

Explanation

An RCD measures the vector sum of currents in the live and neutral conductors; a residual current indicates leakage to earth, and the device trips at its rated residual operating current. It therefore provides protection against earth fault currents, including those too small to operate overcurrent devices.

Question 4Electrical Safety and Standards

Which document is the foundational IEC standard for the effects of current on human beings and livestock?

  1. IEC 60479 Correct answer.
  2. IEC 60364
  3. IEC 60947
  4. IEC 61439

Explanation

IEC 60479 deals with the effects of current passing through the human body and on livestock, providing the physiological basis for protective measures. IEC 60364 covers low-voltage installations, IEC 60947 covers switchgear, and IEC 61439 covers assemblies.

Question 5Electrical Safety and Standards

What does the IP code first characteristic numeral indicate on electrical equipment?

  1. The degree of protection against ingress of water
  2. The maximum ambient temperature of operation
  3. The impact resistance of the enclosure
  4. The degree of protection against ingress of solid foreign objects Correct answer.

Explanation

In the IP code, the first digit after IP specifies protection against access to hazardous parts and against ingress of solid foreign objects. The second digit specifies protection against water ingress, and impact resistance is covered by a separate IK rating.

Question 6Electrical Safety and Standards

Which protective measure relies on limiting the prospective touch voltage and the disconnection time according to the supply system and the nominal voltage?

  1. Protection by total insulation of live parts
  2. Protection by placing out of reach
  3. Protection by use of class II equipment only
  4. Protection by automatic disconnection of supply Correct answer.

Explanation

Automatic disconnection of supply requires that a fault causes protective devices to operate within a time related to the touch voltage limit and the system earthing arrangement. The disconnection times in IEC 60364-4-41 depend on the nominal voltage and whether the system is TN or TT.

Question 7Electrical Safety and Standards

What is the purpose of equipotential bonding in an electrical installation?

  1. To increase the earth electrode resistance to limit leakage current
  2. To provide a low-impedance path for normal load current
  3. To reduce potential differences between simultaneously accessible conductive parts Correct answer.
  4. To isolate metallic services from the earthing system

Explanation

Equipotential bonding connects exposed conductive parts and extraneous conductive parts so that potential differences between them are minimised. This reduces the risk of shock from touch voltages during faults.

Question 8Electrical Safety and Standards

Which class of equipment relies on basic insulation plus supplementary insulation, or reinforced insulation, for protection against electric shock?

  1. Class I
  2. Class III
  3. Class 0
  4. Class II Correct answer.

Explanation

Class II equipment provides protection by double or reinforced insulation and does not rely on a protective earth connection. Class I relies on basic insulation plus a protective conductor, and Class III operates at safety extra-low voltage.

Question 9Electrical Safety and Standards

A TN system has a nominal line-to-neutral voltage of 230 V. According to IEC 60364-4-41, what is the maximum disconnection time for final circuits not exceeding 32 A in this TN system?

  1. 0.4 s Correct answer.
  2. 0.2 s
  3. 5 s
  4. 0.1 s

Explanation

For TN systems at 230 V, IEC 60364-4-41 specifies a maximum disconnection time of 0.4 s for final circuits rated up to 32 A. The 5 s value applies to distribution circuits, and 0.2 s applies to TT systems at the same voltage.

Question 10Electrical Safety and Standards

An RCD with a rated residual operating current of 30 mA is installed to provide additional protection. What does this rating represent?

  1. The rated current of the protected circuit
  2. The maximum earth fault loop impedance the device can tolerate
  3. The residual current at which the device is designed to operate Correct answer.
  4. The short-circuit withstand rating of the device

Explanation

The rated residual operating current IΔn is the residual current value at which the RCD is intended to trip. A 30 mA device provides additional protection against shock in accordance with IEC 60364-4-41.

Question 11Electrical Safety and Standards

In a TT system, why is an RCD often necessary for fault protection?

  1. Because the protective conductor carries normal load current
  2. Because the supply is always at safety extra-low voltage
  3. Because the earth fault loop impedance is generally too high for overcurrent devices to disconnect within the required time Correct answer.
  4. Because the neutral conductor is combined with the protective conductor

Explanation

In a TT system the fault loop includes the local earth electrode and the supply earth, giving a relatively high loop impedance that limits fault current. Overcurrent devices may therefore not operate within the required disconnection time, so RCDs are commonly used.

Question 12Electrical Safety and Standards

What is the main purpose of the IEC 60529 IP code second characteristic numeral?

  1. To specify protection against access to hazardous parts
  2. To specify protection against ingress of water Correct answer.
  3. To specify protection against mechanical impact
  4. To specify protection against corrosive atmospheres

Explanation

The second characteristic numeral of the IP code indicates the degree of protection against harmful ingress of water. Protection against access to hazardous parts and solid objects is given by the first numeral.

Question 13Electrical Safety and Standards

A circuit is protected by a 16 A type B miniature circuit breaker. Which statement correctly describes its magnetic trip range?

  1. It trips magnetically between 3 and 5 times its rated current Correct answer.
  2. It trips magnetically between 10 and 20 times its rated current
  3. It trips magnetically at exactly 16 times its rated current
  4. It trips magnetically between 5 and 10 times its rated current

Explanation

A type B MCB has a magnetic trip threshold of 3 to 5 times the rated current, suitable for resistive loads with low inrush. Types C and D have higher magnetic thresholds, at 5 to 10 and 10 to 20 times respectively.

Question 14Electrical Safety and Standards

Which condition must be satisfied for protection against indirect contact by automatic disconnection in a TN system?

  1. The earth fault loop impedance must be low enough that the fault current causes disconnection within the specified time Correct answer.
  2. The installation must be supplied at safety extra-low voltage
  3. The neutral conductor must be disconnected simultaneously with the live conductors
  4. The earth electrode resistance must be below 100 ohms

Explanation

In TN systems, the disconnection requirement is expressed as a maximum earth fault loop impedance Zs so that the prospective fault current trips the protective device within the tabulated time. This is the basis of the Zs verification in IEC 60364-4-41 and IEC 60364-6.

Question 15Electrical Safety and Standards

What is the function of a surge protective device (SPD) installed at the origin of an installation?

  1. To compensate reactive power in the installation
  2. To limit transient overvoltages and divert surge current to earth Correct answer.
  3. To provide isolation for maintenance work
  4. To interrupt earth fault current within 0.4 s

Explanation

An SPD limits transient overvoltages by diverting surge current, typically to earth, protecting downstream equipment. Its selection and installation are addressed in IEC 61643 and IEC 60364-5-53.

Question 16Electrical Safety and Standards

Which of the following correctly describes the difference between basic insulation and supplementary insulation?

  1. Basic insulation and supplementary insulation are identical in function and location
  2. Basic insulation is applied only to earthing conductors, while supplementary insulation is applied to live parts
  3. Basic insulation provides protection against direct contact, while supplementary insulation is an additional layer independent of the basic insulation Correct answer.
  4. Basic insulation is required only in Class III equipment, while supplementary insulation is required in Class I equipment

Explanation

Basic insulation is the primary insulation applied to live parts to provide basic protection. Supplementary insulation is an independent additional layer that, together with the basic insulation, forms double insulation.

Question 17Electrical Safety and Standards

What does the term 'prospective short-circuit current' refer to at a point in an installation?

  1. The current carried by the protective conductor during normal operation
  2. The residual current that trips an RCD
  3. The current that would flow if a short circuit of negligible impedance occurred at that point Correct answer.
  4. The normal operating current of the connected load

Explanation

Prospective short-circuit current is the current that would flow under a bolted short circuit of negligible impedance at the point of consideration. It is used to verify that protective devices can safely break the fault current.

Question 18Electrical Safety and Standards

A 30 mA RCD is used for additional protection. Which condition must be met regarding its use?

  1. It must be the sole means of protection against direct contact
  2. It must be combined with a voltage-operated earth fault device
  3. It must be installed only on circuits rated above 63 A
  4. It must not replace the basic protective measures required for the circuit Correct answer.

Explanation

Additional protection by a 30 mA RCD supplements, but does not replace, the basic measures such as insulation, barriers, and automatic disconnection. IEC 60364-4-41 permits its use for socket-outlets and certain locations as an extra safeguard.

Question 19Electrical Safety and Standards

Which standard series provides requirements for low-voltage electrical installations, including protection against electric shock?

  1. IEC 60364 Correct answer.
  2. IEC 60204
  3. IEC 60079
  4. IEC 61000

Explanation

IEC 60364 is the series of standards for low-voltage electrical installations and includes Part 4-41 on protection against electric shock. IEC 60079 covers explosive atmospheres, IEC 61000 covers EMC, and IEC 60204 covers electrical equipment of machines.

Question 20Electrical Safety and Standards

Why is a PEN conductor prohibited downstream of an RCD in a TN-C-S system?

  1. Because the RCD would not detect residual current if the PEN carried part of the load return current Correct answer.
  2. Because the RCD would trip at every load change
  3. Because the PEN conductor would short-circuit the RCD terminals
  4. Because a PEN conductor cannot carry load current

Explanation

If a PEN conductor is used on the load side of an RCD, part of the return current can flow through the protective path, bypassing the RCD sensing element. This can defeat detection of residual current and is therefore not permitted.

Question 21Electrical Safety and Standards

A designer is verifying that a 230 V TN final circuit is protected by a 32 A type C MCB. The measured earth fault loop impedance is 1.1 ohms. Using the rule Zs × Ia ≤ U0, what conclusion follows if Ia is taken as 10 times the rated current?

  1. The circuit complies only if an RCD is added
  2. The circuit does not comply because the required fault current is not achieved Correct answer.
  3. The circuit complies because Zs is below the maximum permitted value
  4. The circuit complies because the MCB rating exceeds the fault current

Explanation

For a type C device, Ia is 10 × 32 A = 320 A, so the maximum Zs is 230/320 ≈ 0.72 ohms. The measured 1.1 ohms exceeds this, so the device would not trip within the required time and the circuit does not comply.

Question 22Electrical Safety and Standards

In a TT system with a 230 V supply, a 30 mA RCD provides fault protection. If the earth electrode resistance is 100 ohms, what is the approximate prospective earth fault current, and does it exceed the RCD residual operating current?

  1. About 23 mA, which is below 30 mA
  2. About 2.3 A, which exceeds 30 mA Correct answer.
  3. About 230 mA, which exceeds 30 mA
  4. About 0.23 A, which is below 30 mA

Explanation

The earth fault current is approximately U0 divided by the earth electrode resistance, giving 230/100 = 2.3 A. This greatly exceeds the 30 mA residual operating current, so the RCD would operate, although touch voltage considerations must also be checked.

Question 23Electrical Safety and Standards

Which statement correctly distinguishes double insulation from reinforced insulation?

  1. Double insulation is used only in Class I equipment, while reinforced insulation is used only in Class III equipment
  2. Double insulation comprises basic plus supplementary insulation, while reinforced insulation is a single system providing the same degree of protection Correct answer.
  3. Double insulation and reinforced insulation differ only in colour coding
  4. Double insulation provides protection against water ingress, while reinforced insulation provides protection against impact

Explanation

Double insulation consists of basic insulation plus supplementary insulation, whereas reinforced insulation is a single insulation system designed to provide a degree of protection equivalent to double insulation. Both are associated with Class II equipment.

Question 24Electrical Safety and Standards

A circuit protected by a 63 A type B MCB has a measured earth fault loop impedance of 0.9 ohms at 230 V. Using the 5 times magnetic threshold, what is the maximum permitted Zs and does the circuit comply?

  1. About 0.73 ohms, so it does not comply Correct answer.
  2. About 1.46 ohms, so it complies
  3. About 0.73 ohms, so it complies
  4. About 3.65 ohms, so it complies

Explanation

For a type B device the upper magnetic threshold is 5 × 63 A = 315 A, giving a maximum Zs of 230/315 ≈ 0.73 ohms. The measured 0.9 ohms exceeds this, so disconnection within the required time is not assured.

Question 25Electrical Safety and Standards

Which combination of measures best reflects the principle of protection against direct contact in low-voltage installations?

  1. Class I equipment and a protective conductor only
  2. Use of a PEN conductor and a local earth electrode
  3. Automatic disconnection of supply and equipotential bonding only
  4. Basic insulation of live parts, barriers or enclosures, and, where required, additional protection by a 30 mA RCD Correct answer.

Explanation

Protection against direct contact is achieved primarily by insulating live parts or enclosing them behind barriers and enclosures. Additional protection by a 30 mA RCD may be required in certain locations or for socket-outlets, complementing these measures.

Question 26Electrical Safety and Standards

A final circuit in a 230/400 V TN-S installation is protected by a 20 A type B miniature circuit breaker. Using the conventional 0.4 s disconnection time for final circuits up to 32 A, what is the maximum permitted earth fault loop impedance according to IEC 60364-4-41?

  1. 1.15 ohm Correct answer.
  2. 2.30 ohm
  3. 0.29 ohm
  4. 0.575 ohm

Explanation

For a type B breaker the instantaneous magnetic trip occurs at 5 times the rated current, so a 20 A device trips magnetically at 100 A. The maximum earth fault loop impedance is U0 divided by this current, i.e. 230 V / 100 A = 2.30 ohm, and the 0.4 s disconnection time for final circuits up to 32 A is achieved by this magnetic operation. The tabulated value for a 20 A type B device is therefore 2.30 ohm, not the figure obtained by dividing by the full rated current.

Question 27Electrical Safety and Standards

Which document in the IEC 60364 series sets out the general requirements for electrical installations, including fundamental principles, definitions and the structure of the remaining parts?

  1. IEC 60364-6
  2. IEC 60364-4-41
  3. IEC 60364-5-54
  4. IEC 60364-1 Correct answer.

Explanation

IEC 60364-1 contains the fundamental principles, definitions and the overall structure that the other parts of the series build on. The numbered parts that follow address particular topics such as protection, selection of equipment and verification. Knowing this structure helps a designer locate the correct clause when a requirement is disputed.

Question 28Electrical Safety and Standards

A metal enclosure of Class I equipment is fed from a 230 V TN system and the protective conductor is accidentally interrupted. Which statement correctly describes the protective principle that is lost and the resulting hazard?

  1. The equipment automatically reverts to Class II protection because supplementary insulation is present
  2. Fault current can no longer return via the protective conductor, so the enclosure may remain at a dangerous touch voltage until someone contacts it Correct answer.
  3. The basic insulation is bypassed, so the enclosure becomes live only during a lightning surge
  4. The overcurrent device will still operate because the enclosure provides an alternative return path through the building structure

Explanation

In Class I equipment the exposed metalwork is connected to the protective conductor so that an insulation fault produces a low-impedance earth fault current that trips the overcurrent device. If that conductor is interrupted, the fault current has no dependable return path and the protective device may not operate, leaving the enclosure at a hazardous potential. This is why protective conductor continuity is verified during inspection and testing.

Question 29Electrical Safety and Standards

What is the primary purpose of the IP first characteristic numeral in the IEC 60529 classification?

  1. To indicate the maximum ambient temperature at which the enclosure may be operated
  2. To indicate the degree of protection against ingress of solid foreign objects and against access to hazardous parts Correct answer.
  3. To indicate the rated impulse withstand voltage of the enclosure
  4. To indicate the degree of protection against ingress of water under specified test conditions

Explanation

The first digit of an IP code rates protection of persons against access to hazardous parts and protection of the equipment against ingress of solid foreign objects. Protection against water is expressed by the second digit. The two numerals are independent ratings and must not be confused when specifying equipment for a location.

Question 30Electrical Safety and Standards

During verification of a TN installation, an inspector finds that the earth fault loop impedance of a final circuit exceeds the maximum value permitted for the installed protective device. Which corrective action best restores compliance with IEC 60364-4-41?

  1. Increase the rating of the overcurrent device so that it is less sensitive to the fault current
  2. Remove the circuit protective conductor and rely on the main equipotential bonding alone
  3. Reduce the loop impedance by increasing the protective conductor cross-section or shortening the run, or fit a device whose trip characteristic suits the measured impedance Correct answer.
  4. Record the measured value and take no action provided the circuit is lightly loaded

Explanation

Automatic disconnection depends on the fault current reaching the instantaneous trip level of the protective device within the required time, so the loop impedance must be below the tabulated maximum. Lowering the impedance, for example with a larger protective conductor or a shorter route, or selecting a device with a suitable trip characteristic, restores the required disconnection. Merely recording the result leaves the installation non-compliant.

Question 31Electrical Theory and Fundamentals

In a DC circuit, a resistor of 12 ohms carries a current of 0.5 A. What is the voltage across the resistor?

  1. 12.5 V
  2. 6 V Correct answer.
  3. 0.04 V
  4. 24 V

Explanation

Ohm's law states that voltage equals current multiplied by resistance (V = I × R). Multiplying 0.5 A by 12 ohms gives 6 V, so the potential difference across the resistor is 6 volts.

Question 32Electrical Theory and Fundamentals

A 240 V single-phase load draws 10 A at unity power factor. What is the real power consumed by the load?

  1. 24000 W
  2. 2400 W Correct answer.
  3. 24 W
  4. 240 W

Explanation

For a single-phase circuit, real power equals voltage times current times power factor (P = V × I × cos φ). With unity power factor, cos φ is 1, so 240 V × 10 A × 1 = 2400 W.

Question 33Electrical Theory and Fundamentals

Which statement correctly describes the relationship between current, charge, and time?

  1. One ampere equals one coulomb of charge passing a point per second Correct answer.
  2. One ampere equals one watt of power dissipated per second
  3. One ampere equals one coulomb of charge passing a point per minute
  4. One ampere equals one joule of energy delivered per second

Explanation

Electric current is defined as the rate of flow of electric charge, measured in coulombs per second. One ampere is exactly one coulomb passing a given point in one second (I = Q / t).

Question 34Electrical Theory and Fundamentals

Three resistors of 4 ohms, 6 ohms, and 12 ohms are connected in parallel. What is the equivalent resistance of the combination?

  1. 7.33 ohms
  2. 22 ohms
  3. 0.5 ohms
  4. 2 ohms Correct answer.

Explanation

For parallel resistors, the reciprocal of the equivalent resistance equals the sum of the reciprocals: 1/R = 1/4 + 1/6 + 1/12 = 3/12 + 2/12 + 1/12 = 6/12. Therefore R = 12/6 = 2 ohms.

Question 35Electrical Theory and Fundamentals

A coil has an inductive reactance of 30 ohms and a resistance of 40 ohms in series. What is the magnitude of the total impedance?

  1. 10 ohms
  2. 70 ohms
  3. 35 ohms
  4. 50 ohms Correct answer.

Explanation

In a series RL circuit, impedance magnitude is the vector sum of resistance and reactance: Z = √(R² + X_L²). Here √(40² + 30²) = √(1600 + 900) = √2500 = 50 ohms.

Question 36Electrical Theory and Fundamentals

In a purely capacitive AC circuit, how does the current relate to the voltage?

  1. Current leads the voltage by 45 degrees
  2. Current is in phase with the voltage
  3. Current lags the voltage by 90 degrees
  4. Current leads the voltage by 90 degrees Correct answer.

Explanation

In a capacitor, current is proportional to the rate of change of voltage, so the current reaches its peak a quarter cycle before the voltage. This is described as current leading voltage by 90 electrical degrees.

Question 37Electrical Theory and Fundamentals

What is the primary function of a transformer in an AC power system?

  1. To increase the frequency of the supply for transmission
  2. To store electrical energy in an electric field between windings
  3. To change AC voltage levels through mutual induction between windings Correct answer.
  4. To convert AC power into DC power for distribution

Explanation

A transformer transfers energy between two windings linked by a common magnetic core. By having different turns ratios, it steps AC voltage up or down while approximately conserving power.

Question 38Electrical Theory and Fundamentals

A transformer has 500 primary turns and 100 secondary turns. If the primary is supplied at 400 V, what is the secondary voltage (assume an ideal transformer)?

  1. 2000 V
  2. 80 V Correct answer.
  3. 100 V
  4. 400 V

Explanation

For an ideal transformer, the voltage ratio equals the turns ratio: V_s / V_p = N_s / N_p. Thus V_s = 400 × (100/500) = 400 × 0.2 = 80 V.

Question 39Electrical Theory and Fundamentals

Which material property primarily determines whether a substance is classified as a conductor, semiconductor, or insulator?

  1. Its physical length along the current path
  2. The cross-sectional area of the sample
  3. The temperature of the surrounding environment alone
  4. The width of the energy gap between its valence and conduction bands Correct answer.

Explanation

Conductors have overlapping or very narrow band gaps so electrons move freely; semiconductors have a moderate gap; insulators have a wide gap. The band-gap width is the fundamental classification criterion.

Question 40Electrical Theory and Fundamentals

A 100 W lamp operates at 200 V. What current does it draw?

  1. 2 A
  2. 0.5 A Correct answer.
  3. 50 A
  4. 20000 A

Explanation

Power equals voltage times current (P = V × I), so current equals power divided by voltage. Dividing 100 W by 200 V gives 0.5 A.

Question 41Electrical Theory and Fundamentals

Two capacitors of 6 microfarads and 3 microfarads are connected in series. What is the equivalent capacitance?

  1. 2 microfarads Correct answer.
  2. 4.5 microfarads
  3. 18 microfarads
  4. 9 microfarads

Explanation

Capacitors in series combine like resistors in parallel: 1/C = 1/C1 + 1/C2. Here 1/C = 1/6 + 1/3 = 1/6 + 2/6 = 3/6, so C = 2 microfarads.

Question 42Electrical Theory and Fundamentals

What is the effect on the total resistance of a circuit when an additional resistor is connected in parallel with an existing resistor?

  1. The total resistance becomes the arithmetic sum of the two values
  2. The total resistance increases above the largest individual resistance
  3. The total resistance stays equal to the largest individual resistance
  4. The total resistance decreases below the smallest individual resistance Correct answer.

Explanation

Adding a parallel path provides an additional route for current, so the equivalent resistance always falls. The combined value is always less than the smallest of the individual resistances.

Question 43Electrical Theory and Fundamentals

A sinusoidal voltage has a peak value of 340 V. What is its approximate RMS value?

  1. 340 V
  2. 680 V
  3. 240 V Correct answer.
  4. 170 V

Explanation

For a sine wave, RMS value equals peak value divided by the square root of 2 (about 1.414). Dividing 340 V by 1.414 gives approximately 240 V.

Question 44Electrical Theory and Fundamentals

Which of the following best describes the function of a capacitor in an electrical circuit?

  1. It stores energy in an electrostatic field and opposes changes in voltage Correct answer.
  2. It stores energy in a magnetic field and opposes changes in current
  3. It converts electrical energy directly into mechanical work
  4. It maintains a constant current regardless of the applied voltage

Explanation

A capacitor accumulates charge on two plates separated by a dielectric, storing energy in an electric field. Because voltage across it cannot change instantaneously, it opposes rapid voltage changes.

Question 45Electrical Theory and Fundamentals

A circuit has a real power of 800 W and an apparent power of 1000 VA. What is the power factor?

  1. 0.6
  2. 0.8 Correct answer.
  3. 0.2
  4. 1.25

Explanation

Power factor is the ratio of real power to apparent power (PF = P / S). Dividing 800 W by 1000 VA yields 0.8, a lagging or leading value depending on the reactive element.

Question 46Electrical Theory and Fundamentals

According to Kirchhoff's current law, what is true at any node in a circuit?

  1. The current in each branch is always equal
  2. The algebraic sum of voltage drops around the node is zero
  3. The algebraic sum of currents entering and leaving the node is zero Correct answer.
  4. The total resistance at the node equals the sum of branch resistances

Explanation

Kirchhoff's current law expresses conservation of charge: charge cannot accumulate at a node, so the sum of currents entering equals the sum leaving. Expressed algebraically with sign conventions, the sum is zero.

Question 47Electrical Theory and Fundamentals

A 12 V battery is connected across a series combination of a 3 ohm and a 6 ohm resistor. What is the voltage drop across the 6 ohm resistor?

  1. 12 V
  2. 6 V
  3. 8 V Correct answer.
  4. 4 V

Explanation

Total resistance is 9 ohms, so current is 12/9 = 1.333 A. The drop across 6 ohms is 1.333 × 6 = 8 V, consistent with the voltage-divider rule where the larger resistance takes the larger share.

Question 48Electrical Theory and Fundamentals

What happens to the resistance of a typical metallic conductor when its temperature increases?

  1. Resistance drops to zero at any elevated temperature
  2. Resistance increases because lattice vibrations impede electron flow more Correct answer.
  3. Resistance remains unchanged because the material is metallic
  4. Resistance decreases because more free electrons are released

Explanation

In metals, higher temperature increases atomic lattice vibration, which scatters drifting electrons more frequently. This raises resistivity and therefore resistance, giving a positive temperature coefficient.

Question 49Electrical Theory and Fundamentals

A coil with an inductance of 0.2 H carries a current that changes at 10 A per second. What is the induced voltage across the coil?

  1. 0.2 V
  2. 0.02 V
  3. 2 V Correct answer.
  4. 50 V

Explanation

The voltage induced in an inductor equals inductance times the rate of change of current (V = L × di/dt). Multiplying 0.2 H by 10 A/s gives 2 V.

Question 50Electrical Theory and Fundamentals

In a three-phase star (wye) connected system with a line voltage of 400 V, what is the phase voltage?

  1. 400 V
  2. 231 V Correct answer.
  3. 133 V
  4. 693 V

Explanation

In a star connection, phase voltage equals line voltage divided by the square root of 3. Dividing 400 V by 1.732 gives approximately 231 V.