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SPM Electrical & Electronics Engineering Studies practice questions

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Question 1Electrical and Electronic Fundamentals, Units and Safety

Which SI base unit is used to express electric current in the SPM electrical and electronics syllabus?

  1. Coulomb
  2. Volt
  3. Ohm
  4. Ampere Correct answer.

Explanation

The ampere is one of the seven SI base units and measures electric current, defined as one coulomb of charge passing a point per second. The other three quantities are derived units built from base units.

Question 2Electrical and Electronic Fundamentals, Units and Safety

A resistor of 220 Ω carries a current of 0.05 A. What is the potential difference across it?

  1. 0.0023 V
  2. 4400 V
  3. 11 V Correct answer.
  4. 4.4 V

Explanation

Ohm's law states V = IR, so multiplying 0.05 A by 220 Ω gives 11 V. The result is a sensible low-voltage value for a small resistor.

Question 3Electrical and Electronic Fundamentals, Units and Safety

Which statement correctly describes the function of a fuse in a domestic circuit?

  1. It converts excess current into useful light energy
  2. It reduces the voltage supplied to each appliance
  3. It stores charge to smooth the supply current
  4. It melts and breaks the circuit when current exceeds its rating Correct answer.

Explanation

A fuse contains a thin wire that heats up and melts when the current exceeds its rated value, opening the circuit and preventing overheating or fire. It protects the wiring and the appliance but does not regulate voltage or store charge.

Question 4Electrical and Electronic Fundamentals, Units and Safety

In a series circuit containing three identical lamps and one cell, what is true of the current?

  1. The current is the same at every point in the circuit Correct answer.
  2. The current is zero in the last lamp
  3. The current halves after each lamp is passed
  4. The current is largest in the lamp nearest the cell

Explanation

In a series circuit there is only one path for charge, so the same current flows through every component and the cell. Charge is neither used up nor stored by the lamps.

Question 5Electrical and Electronic Fundamentals, Units and Safety

A mains plug in Malaysia is fitted with a three-pin arrangement. What is the purpose of the earth pin?

  1. To provide a low-resistance path to earth if the metal casing becomes live Correct answer.
  2. To carry the working current back to the supply substation
  3. To switch the appliance off automatically when unplugged
  4. To reduce the voltage reaching the appliance

Explanation

The earth wire connects the metal casing of an appliance to earth, so a fault that makes the casing live causes a large current that blows the fuse or trips the breaker. This protects the user from electric shock.

Question 6Electrical and Electronic Fundamentals, Units and Safety

Which quantity is measured in joules per coulomb?

  1. Potential difference Correct answer.
  2. Power
  3. Electric charge
  4. Resistance

Explanation

One joule per coulomb defines the volt, the unit of potential difference. It expresses the energy transferred per unit charge passing between two points.

Question 7Electrical and Electronic Fundamentals, Units and Safety

A 12 V battery supplies a 60 Ω lamp. What power is dissipated by the lamp?

  1. 2.4 W Correct answer.
  2. 720 W
  3. 0.2 W
  4. 5 W

Explanation

Using P = V²/R gives 144 divided by 60, which equals 2.4 W. The same answer follows from finding the current of 0.2 A and multiplying by 12 V.

Question 8Electrical and Electronic Fundamentals, Units and Safety

Which material is classified as an insulator in electrical work?

  1. Copper
  2. PVC Correct answer.
  3. Brass
  4. Aluminium

Explanation

PVC has very few free electrons, so it resists the flow of charge and is used to sheath cables. Copper, aluminium and brass are metals with abundant free electrons and therefore conduct well.

Question 9Electrical and Electronic Fundamentals, Units and Safety

Two resistors of 6 Ω and 3 Ω are connected in parallel. What is the combined resistance?

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

Explanation

For two resistors in parallel, R = (R1 × R2)/(R1 + R2) = 18/9 = 2 Ω. The result must be smaller than the smallest branch resistance, which confirms the answer.

Question 10Electrical and Electronic Fundamentals, Units and Safety

A student needs a 4.7 kΩ resistor for a circuit. Which colour code band sequence matches this value for a four-band resistor with 5 percent tolerance?

  1. Yellow, violet, red, gold Correct answer.
  2. Yellow, violet, orange, gold
  3. Yellow, violet, brown, gold
  4. Green, blue, red, silver

Explanation

Yellow is 4, violet is 7 and red is a multiplier of 100, giving 47 × 100 = 4700 Ω. Gold in the fourth band indicates a tolerance of plus or minus 5 percent.

Question 11Electrical and Electronic Fundamentals, Units and Safety

An ammeter is to be used to measure the current through a lamp. How should it be connected?

  1. In series with the lamp, with a very high internal resistance
  2. In series with the lamp, with a very low internal resistance Correct answer.
  3. In parallel with the lamp, with a very low internal resistance
  4. In parallel with the lamp, with a very high internal resistance

Explanation

An ammeter must carry the current being measured, so it is placed in series and given a low resistance to avoid changing the circuit current. A high resistance in series would reduce the current being measured.

Question 12Electrical and Electronic Fundamentals, Units and Safety

A 240 V mains appliance draws 5 A. Which fuse rating is the most suitable choice?

  1. 5 A
  2. 1 A
  3. 3 A
  4. 13 A Correct answer.

Explanation

The appliance needs a fuse rated slightly above its normal working current so it does not blow in use but still protects the cable. The standard 13 A plug fuse is the smallest standard rating above 5 A.

Question 13Electrical and Electronic Fundamentals, Units and Safety

Which hazard is most directly associated with a loose live wire touching the metal casing of a Class I appliance?

  1. Electric shock to a user touching the casing Correct answer.
  2. Increased frequency of the mains supply
  3. Permanent magnetisation of the casing
  4. Reduced power consumption by the appliance

Explanation

If the live conductor contacts the metal casing, the casing becomes live at mains potential. A person touching it and an earthed object completes a circuit through the body, causing a severe shock unless the earth path trips the protection.

Question 14Electrical and Electronic Fundamentals, Units and Safety

Which unit is equivalent to one watt?

  1. One volt per ampere
  2. One joule per second Correct answer.
  3. One newton per metre
  4. One coulomb per second

Explanation

Power is the rate of energy transfer, so one watt equals one joule of energy transferred each second. This follows directly from the definition P = E/t.

Question 15Electrical and Electronic Fundamentals, Units and Safety

A cell of 1.5 V drives a current of 0.3 A through a bulb. How much charge passes through the bulb in 20 s?

  1. 30 C
  2. 6 C Correct answer.
  3. 0.45 C
  4. 0.015 C

Explanation

Charge is current multiplied by time, so 0.3 A × 20 s = 6 C. The cell voltage is not needed for this calculation, which is a common distractor.

Question 16Electrical and Electronic Fundamentals, Units and Safety

Two 100 Ω resistors are connected in parallel across a 10 V supply. What current flows from the supply?

  1. 0.05 A
  2. 0.2 A Correct answer.
  3. 2 A
  4. 0.1 A

Explanation

The parallel combination is 50 Ω, so the supply current is 10 V divided by 50 Ω, which is 0.2 A. Each branch carries 0.1 A and the branches add.

Question 17Electrical and Electronic Fundamentals, Units and Safety

A copper cable is chosen for domestic wiring rather than a similar PVC rod. Which property best explains this choice?

  1. Copper has a very high resistivity
  2. Copper is an insulator at room temperature
  3. Copper has many free electrons and low resistivity Correct answer.
  4. Copper has no free electrons in its lattice

Explanation

Metals such as copper have a lattice with delocalised electrons that move freely under a potential difference, giving low resistivity. This allows cables of modest thickness to carry household currents without excessive heating.

Question 18Electrical and Electronic Fundamentals, Units and Safety

A 2 kW electric kettle is used for 5 minutes. How much electrical energy does it transfer?

  1. 10 kWh
  2. 600 kJ Correct answer.
  3. 10 kJ
  4. 0.6 J

Explanation

Energy is power multiplied by time, so 2000 W × 300 s = 600 000 J, which is 600 kJ. The time must be converted to seconds before multiplying.

Question 19Electrical and Electronic Fundamentals, Units and Safety

Which statement best explains why the live wire is connected through the switch in a lighting circuit?

  1. So the lamp receives a higher voltage when switched on
  2. So the lamp is at earth potential when the switch is open Correct answer.
  3. So the fuse rating can be reduced
  4. So the neutral wire carries the full mains voltage

Explanation

Switching the live conductor isolates the lamp from the high potential, leaving it connected only to neutral at near-earth potential. This reduces the shock risk during lamp changes.

Question 20Electrical and Electronic Fundamentals, Units and Safety

A resistor has a value of 4700 Ω. Which prefix form is correct?

  1. 47 kΩ
  2. 0.47 kΩ
  3. 4.7 kΩ Correct answer.
  4. 470 kΩ

Explanation

The prefix kilo means one thousand, so 4700 Ω divided by 1000 gives 4.7 kΩ. Moving the decimal point three places to the left converts ohms to kilohms.

Question 21Electrical and Electronic Fundamentals, Units and Safety

A 12 V supply is connected across a potential divider made of a 4 kΩ and a 2 kΩ resistor in series. What is the voltage across the 2 kΩ resistor?

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

Explanation

The total resistance is 6 kΩ, so the current is 12 V divided by 6000 Ω, which is 2 mA. Multiplying 2 mA by 2000 Ω gives 4 V across the 2 kΩ resistor.

Question 22Electrical and Electronic Fundamentals, Units and Safety

Which combination of protective devices gives the fastest disconnection for a live-to-earth fault in a modern domestic installation?

  1. A residual current device with a 30 mA trip current Correct answer.
  2. A double-pole isolator switch
  3. A 13 A cartridge fuse in the plug
  4. A miniature circuit breaker rated at 32 A

Explanation

An RCD monitors the difference between live and neutral currents and trips within milliseconds at 30 mA, well below the level likely to cause fatal shock. Fuses and MCBs respond to overcurrent and may take much longer at low fault currents.

Question 23Electrical and Electronic Fundamentals, Units and Safety

A student measures 0.50 A through a resistor using an ammeter with a 2 percent reading error and reads 24.0 V from a voltmeter with a 1 percent reading error. What is the percentage uncertainty in the calculated resistance?

  1. 0.5 percent
  2. 3 percent Correct answer.
  3. 1 percent
  4. 2 percent

Explanation

Resistance is calculated by dividing voltage by current, so the percentage uncertainties add: 1 percent plus 2 percent gives 3 percent. Uncertainties add for both multiplication and division.

Question 24Electrical and Electronic Fundamentals, Units and Safety

A 1.5 V cell with an internal resistance of 0.5 Ω is connected to a 2.5 Ω resistor. What is the terminal potential difference across the resistor?

  1. 1.25 V Correct answer.
  2. 1.5 V
  3. 0.25 V
  4. 1.0 V

Explanation

The total circuit resistance is 3.0 Ω, so the current is 1.5 V divided by 3.0 Ω, which is 0.5 A. The terminal voltage is then 0.5 A × 2.5 Ω = 1.25 V, showing the drop across the internal resistance.

Question 25Electrical and Electronic Fundamentals, Units and Safety

Why is a ring final circuit, rather than a simple radial circuit, used for socket outlets in many domestic installations?

  1. It guarantees that every socket receives the full supply voltage
  2. It removes the need for any circuit protection device
  3. It prevents current from flowing in the neutral conductor
  4. Each cable carries roughly half the load current, allowing thinner conductors Correct answer.

Explanation

In a ring circuit the load current has two paths from the consumer unit, so each leg carries about half the total current. This allows smaller conductors to serve the same sockets, with the protective device sized to protect the cable.

Question 26Electrical and Electronic Fundamentals, Units and Safety

A resistor is marked with the colour bands brown, black, red, and gold. What is its resistance and tolerance?

  1. 1 MΩ ±5%
  2. 1 kΩ ±5% Correct answer.
  3. 100 Ω ±10%
  4. 10 Ω ±5%

Explanation

In the four-band code, brown = 1, black = 0, red = multiplier ×100, giving 10 × 100 = 1000 Ω = 1 kΩ. Gold in the fourth band indicates a tolerance of ±5%.

Question 27Electrical and Electronic Fundamentals, Units and Safety

A 12 V car battery is connected to a 3 Ω resistor. What current flows through the resistor?

  1. 9 A
  2. 0.25 A
  3. 4 A Correct answer.
  4. 36 A

Explanation

Ohm's law states I = V / R. Substituting V = 12 V and R = 3 Ω gives I = 12 / 3 = 4 A.

Question 28Electrical and Electronic Fundamentals, Units and Safety

A 100 W lamp is left switched on for 8 hours. How much energy does it transfer in kilowatt-hours?

  1. 12.5 kWh
  2. 800 kWh
  3. 8 kWh
  4. 0.8 kWh Correct answer.

Explanation

Energy in kWh equals power in kW multiplied by time in hours. The lamp uses 100 W = 0.1 kW, so energy = 0.1 × 8 = 0.8 kWh.

Question 29Electrical and Electronic Fundamentals, Units and Safety

A 1.5 V cell is connected to a 1.0 Ω resistor and a 2.0 Ω resistor in series. What is the voltage across the 2.0 Ω resistor?

  1. 1.5 V
  2. 0.5 V
  3. 1.0 V Correct answer.
  4. 3.0 V

Explanation

The total resistance is 1.0 + 2.0 = 3.0 Ω, so the current is I = V / R = 1.5 / 3.0 = 0.5 A. The voltage across the 2.0 Ω resistor is V = I × R = 0.5 × 2.0 = 1.0 V.

Question 30Electrical and Electronic Fundamentals, Units and Safety

A 230 V appliance has a power rating of 2.3 kW. Which standard fuse rating is the most suitable for protecting its circuit?

  1. 20 A
  2. 13 A Correct answer.
  3. 3 A
  4. 5 A

Explanation

The normal current is I = P / V = 2300 / 230 = 10 A. A 13 A fuse is the smallest standard rating above 10 A, so it carries the normal current without nuisance blowing while still protecting the circuit.

Question 31Electrical Circuits and Network Principles

Which quantity is defined as the rate of flow of electric charge past a point in a circuit?

  1. Potential difference
  2. Electromotive force
  3. Resistance
  4. Electric current Correct answer.

Explanation

Electric current is the rate at which charge passes a point, measured in amperes where one ampere equals one coulomb per second. Electromotive force and potential difference are measured in volts and describe energy per unit charge, not charge flow.

Question 32Electrical Circuits and Network Principles

A resistor of 220 Ω carries a current of 50 mA. What is the potential difference across it?

  1. 44 V
  2. 0.23 V
  3. 11 V Correct answer.
  4. 4.4 V

Explanation

Ohm's law gives V = IR, so 0.050 A multiplied by 220 Ω equals 11 V. Converting milliamperes to amperes before multiplying is essential to obtain the correct result.

Question 33Electrical Circuits and Network Principles

Three resistors of 6 Ω, 3 Ω and 2 Ω are connected in parallel. What is the total resistance of the combination?

  1. 3.67 Ω
  2. 11 Ω
  3. 0.5 Ω
  4. 1 Ω Correct answer.

Explanation

For parallel resistors, 1/RT = 1/6 + 1/3 + 1/2 = 1/6 + 2/6 + 3/6 = 6/6 = 1, so RT = 1 Ω. The equivalent resistance is always smaller than the smallest individual branch resistance.

Question 34Electrical Circuits and Network Principles

In a series circuit, which statement about current and voltage is correct?

  1. Current divides among the components and the voltage is the same across each
  2. Current is the same through each component and the supply voltage divides among them Correct answer.
  3. Both current and voltage are the same at every point
  4. Both current and voltage divide in proportion to resistance

Explanation

A series circuit provides a single path, so the same current flows through every component. The supply voltage is shared among the components in proportion to their resistances, in accordance with Kirchhoff's voltage law.

Question 35Electrical Circuits and Network Principles

A 12 V battery supplies a circuit that draws 2 A. How much energy is converted in 5 minutes?

  1. 7200 J Correct answer.
  2. 600 J
  3. 120 J
  4. 24 J

Explanation

Power equals V times I, giving 24 W, and energy equals power times time. Five minutes is 300 seconds, so 24 W multiplied by 300 s equals 7200 J.

Question 36Electrical Circuits and Network Principles

Which statement best describes the function of a capacitor in a DC circuit?

  1. It stores energy in a magnetic field and opposes changes in current
  2. It stores energy in an electric field and blocks steady direct current once charged Correct answer.
  3. It converts alternating current into direct current
  4. It maintains a constant current regardless of load

Explanation

A capacitor stores charge and energy in the electric field between its plates, and once fully charged it blocks steady direct current. Its opposition to current depends on the rate of change of voltage, so it passes changing signals.

Question 37Electrical Circuits and Network Principles

What is the time constant of a circuit containing a 100 kΩ resistor and a 10 µF capacitor?

  1. 0.1 s
  2. 10 s
  3. 1 s Correct answer.
  4. 0.001 s

Explanation

The RC time constant is the product of resistance and capacitance, so 100000 Ω multiplied by 0.00001 F equals 1 s. This value is the time taken to reach about 63 percent of the final voltage when charging.

Question 38Electrical Circuits and Network Principles

Which property of a coil opposes a change in the current flowing through it?

  1. Conductance
  2. Inductance Correct answer.
  3. Reluctance
  4. Capacitance

Explanation

Inductance is the property that causes a back electromotive force proportional to the rate of change of current, opposing any change in current. It arises from the magnetic field linking the coil's turns.

Question 39Electrical Circuits and Network Principles

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

  1. 480 V
  2. 240 V Correct answer.
  3. 340 V
  4. 170 V

Explanation

For a sine wave, the RMS value equals the peak value divided by the square root of two, so 340 V divided by 1.414 gives about 240 V. The RMS value is the equivalent heating effect of the waveform.

Question 40Electrical Circuits and Network Principles

Two sinusoidal waveforms of the same frequency are described as being in phase when they:

  1. have equal amplitudes
  2. differ in phase by 90 degrees
  3. reach corresponding points of their cycles at the same instant Correct answer.
  4. have frequencies in a ratio of two to one

Explanation

Two waveforms are in phase when their zero crossings and peaks coincide in time, giving a phase difference of zero degrees. Amplitude and frequency ratio do not determine phase relationship.

Question 41Electrical Circuits and Network Principles

A coil has a reactance of 60 Ω and a resistance of 80 Ω in series. What is the impedance of the coil?

  1. 48 Ω
  2. 100 Ω Correct answer.
  3. 140 Ω
  4. 20 Ω

Explanation

Impedance combines resistance and reactance as a right-angled phasor sum, so Z equals the square root of the sum of the squares of R and XL. The square root of 6400 plus 3600 is the square root of 10000, which is 100 Ω.

Question 42Electrical Circuits and Network Principles

In a purely capacitive AC circuit, the current:

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

Explanation

In a capacitor the current reaches its maximum before the voltage does, so current leads voltage by 90 degrees. The mnemonic CIV states that in a capacitor the current leads the voltage.

Question 43Electrical Circuits and Network Principles

What is the resonant frequency of a series circuit with a 4 mH inductor and a 100 µF capacitor?

  1. About 63 Hz
  2. About 1590 Hz
  3. About 40 Hz
  4. About 252 Hz Correct answer.

Explanation

At resonance the reactances are equal, giving f = 1/(2π√(LC)). The square root of the product equals about 6.32 × 10^-4, and inverting twice gives approximately 252 Hz.

Question 44Electrical Circuits and Network Principles

Which statement correctly describes Kirchhoff's current law at a circuit node?

  1. The sum of the potential differences at a node equals zero
  2. The total current in a branch equals the product of resistance and voltage
  3. The sum of the currents entering a node equals the sum of the currents leaving it Correct answer.
  4. The sum of the voltage drops around any closed loop is zero

Explanation

Kirchhoff's current law expresses conservation of charge: charge cannot accumulate at a node, so the total current entering equals the total current leaving. It is applied to junctions, not to loops.

Question 45Electrical Circuits and Network Principles

A circuit contains two loops. Using Kirchhoff's voltage law, how many independent voltage equations can be written for a two-mesh network with one shared branch?

  1. Four
  2. Three
  3. Two Correct answer.
  4. One

Explanation

Each independent loop in a planar network yields one voltage equation, and a two-mesh circuit has two independent loops. The shared branch is included in both equations, which is why the equations remain independent.

Question 46Electrical Circuits and Network Principles

What does the internal resistance of a cell cause when the cell supplies current?

  1. The terminal voltage rises above the EMF
  2. The terminal voltage falls below the EMF by the product of current and internal resistance Correct answer.
  3. The current becomes independent of the external resistance
  4. The EMF of the cell increases with load

Explanation

The terminal voltage equals the EMF minus the voltage drop across the internal resistance, IR_internal. As load current increases, this internal drop grows and the terminal voltage falls.

Question 47Electrical Circuits and Network Principles

A potential divider uses two resistors of 4 kΩ and 6 kΩ across a 10 V supply. What is the voltage across the 6 kΩ resistor?

  1. 4 V
  2. 10 V
  3. 2.4 V
  4. 6 V Correct answer.

Explanation

In a series divider the voltage across a resistor is proportional to its resistance. The 6 kΩ resistor takes 6/10 of the 10 V supply, giving 6 V.

Question 48Electrical Circuits and Network Principles

What is the main advantage of using a Thévenin equivalent circuit when analysing a complex network?

  1. It converts the network into a current source with a parallel resistance
  2. It increases the power delivered to the load
  3. It reduces the network to a single voltage source and series resistance seen from the load terminals Correct answer.
  4. It eliminates the need to know the load resistance

Explanation

Thévenin's theorem replaces any linear two-terminal network with an equivalent EMF in series with a resistance, simplifying load calculations. The equivalent values are found from the open-circuit voltage and the resistance seen with sources suppressed.

Question 49Electrical Circuits and Network Principles

A Wheatstone bridge is balanced. Which condition must hold?

  1. The galvanometer has infinite resistance
  2. The total resistance of both parallel branches is equal
  3. The supply voltage is zero
  4. The ratio of the two arms on one side equals the ratio of the two arms on the other side Correct answer.

Explanation

A balanced bridge has no current through the galvanometer, which occurs when the resistance ratios of the two arms satisfy R1/R2 = R3/R4. This null condition allows an unknown resistance to be calculated from known values.

Question 50Electrical Circuits and Network Principles

Which instrument connection is correct for measuring the current through a component?

  1. An ammeter connected in parallel with the component
  2. An ammeter connected in series with the component Correct answer.
  3. A voltmeter connected in series with the component
  4. A voltmeter connected in parallel with the ammeter

Explanation

An ammeter must carry the current being measured, so it is connected in series with the component and has a very low resistance. A voltmeter is connected in parallel and has a high resistance to avoid disturbing the circuit.