- Which quantity is measured in coulombs?
- A) Voltage
- B) Current
- C) Charge
- D) Resistance Answer: C) Charge Explanation: Electric charge is the fundamental property measured in coulombs (C). Current is coulombs per second (ampere), voltage is joules per coulomb (volt), and resistance is volt per ampere (ohm).
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- The SI unit of electric current is:
- A) Volt
- B) Ampere
- C) Ohm
- D) Watt Answer: B) Ampere Explanation: The ampere (A) is the unit of current, defined as the rate of flow of electric charge (1 A = 1 C/s).
- Ohm’s law states that:
- A) V = IR
- B) P = VI
- C) Q = It
- D) E = QV Answer: A) V = IR Explanation: Ohm’s law relates voltage (V), current (I), and resistance (R) for ohmic conductors: V is proportional to I with proportionality constant R.
- The unit of resistance is:
- A) Tesla
- B) Newton
- C) Ohm
- D) Farad Answer: C) Ohm Explanation: Resistance opposes current; its SI unit is the ohm (Ω), equal to volt per ampere.
- Which material is typically a good conductor?
- A) Glass
- B) Rubber
- C) Copper
- D) Wood
Answer: C) Copper
Explanation: Metals like copper have free electrons that allow easy charge flow, making them good conductors. Glass, rubber, and dry wood are insulators.
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- The energy consumed by an electrical device is measured in:
- A) Volt-ampere reactive
- B) Kilowatt-hour
- C) Ampere-hour
- D) Henry Answer: B) Kilowatt-hour Explanation: Energy is power over time. Utilities bill in kWh, where 1 kWh = 3.6 × 10^6 joules.
- Current in a series circuit:
- A) Splits across branches
- B) Is the same through each component
- C) Is zero
- D) Depends only on voltage source internal resistance Answer: B) Is the same through each component Explanation: In series, there is only one path, so the same current flows through all components.
- Voltage in a parallel circuit:
- A) Is zero across each branch
- B) Is the same across each branch
- C) Adds across branches
- D) Depends on branch resistance Answer: B) Is the same across each branch Explanation: In parallel, each branch connects to the same two nodes, so each sees the same potential difference.
- The unit of capacitance is:
- A) Weber
- B) Farad
- C) Henry
- D) Siemens Answer: B) Farad Explanation: Capacitance (C) is charge stored per volt: C = Q/V, SI unit farad (F).
- Which component stores energy in an electric field?
- A) Inductor
- B) Resistor
- C) Capacitor
- D) Diode Answer: C) Capacitor Explanation: Capacitors store energy between their plates in an electric field: E = 1/2 C V^2.
- Which component stores energy in a magnetic field?
- A) Capacitor
- B) Inductor
- C) Resistor
- D) Transistor
Answer: B) Inductor
Explanation: Inductors store energy in their magnetic field: E = 1/2 L I^2.
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- The unit of inductance is:
- A) Tesla
- B) Henry
- C) Farad
- D) Weber Answer: B) Henry Explanation: Inductance (L) relates voltage to rate of change of current: v = L di/dt; SI unit is henry (H).
- Which law explains that the sum of currents entering a node equals the sum leaving it?
- A) Ohm’s Law
- B) Faraday’s Law
- C) Kirchhoff’s Current Law (KCL)
- D) Kirchhoff’s Voltage Law (KVL) Answer: C) Kirchhoff’s Current Law (KCL) Explanation: KCL is a statement of charge conservation at a node: net current into a node is zero.
- The algebraic sum of voltages around any closed loop is zero. This is:
- A) KCL
- B) KVL
- C) Lenz’s Law
- D) Coulomb’s Law Answer: B) KVL Explanation: KVL reflects energy conservation: the sum of rises and drops around a loop cancels.
- Power dissipated by a resistor can be expressed as:
- A) P = I/R
- B) P = VI
- C) P = V/I
- D) P = 1/2 CV^2 Answer: B) P = VI Explanation: Electrical power is the product of voltage and current. For resistors, also P = I^2R = V^2/R.
- The conductance unit is:
- A) Siemens
- B) Ohm
- C) Farad
- D) Henry Answer: A) Siemens Explanation: Conductance G is the reciprocal of resistance R: G = 1/R; SI unit siemens (S).
- In metallic conductors, current is due to movement of:
- A) Protons
- B) Neutrons
- C) Electrons
- D) Ions only
Answer: C) Electrons
Explanation: In metals, free electrons drift under an electric field, constituting current.
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- A) V/m
- B) A/m
- C) N·m
- D) C/m Answer: A) V/m Explanation: Electric field E is force per unit charge or voltage per distance; SI unit volt per meter.
- Resistivity depends primarily on:
- A) Length only
- B) Cross-sectional area only
- C) Material and temperature
- D) Applied voltage Answer: C) Material and temperature Explanation: Resistivity is an intrinsic property of the material and varies with temperature; resistance R = ρL/A.
- A 10 Ω resistor with 2 A through it has a voltage drop of:
- A) 5 V
- B) 10 V
- C) 20 V
- D) 0.2 V Answer: C) 20 V Explanation: By Ohm’s law V = IR = 2 A × 10 Ω = 20 V.
- The energy stored in a 100 µF capacitor charged to 10 V is:
- A) 0.005 J
- B) 0.5 J
- C) 5 J
- D) 0.05 J Answer: A) 0.005 J Explanation: E = 1/2 C V^2 = 0.5 × 100e-6 × 100 = 0.005 J.
- The time constant of an RC circuit is:
- A) R/L
- B) L/R
- C) RC
- D) 1/RC Answer: C) RC Explanation: τ = RC sets the exponential rate for charging/discharging a capacitor in a first-order RC network.
- The time constant of an RL circuit is:
- A) R/L
- B) L/R
- C) RC
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- In AC, root-mean-square (RMS) value of a sinusoidal current with peak I_peak is:
- A) I_peak
- B) I_peak/2
- C) I_peak/√2
- D) √2 · I_peak Answer: C) I_peak/√2 Explanation: For a sine wave, Irms = Ipeak/√2; same for Vrms.
- Power factor is defined as:
- A) Apparent power / Real power
- B) Real power / Apparent power
- C) Reactive power / Real power
- D) Apparent power / Reactive power Answer: B) Real power / Apparent power Explanation: PF = P/S = cos φ for sinusoidal steady state; indicates how effectively current contributes to real work.
- Apparent power unit is:
- A) Watt (W)
- B) Var (var)
- C) Volt-ampere (VA)
- D) Joule (J) Answer: C) Volt-ampere (VA) Explanation: Apparent power S = VI (RMS) measured in VA; real power P in watts; reactive power Q in vars.
- A pure inductor in AC causes current to:
- A) Lead voltage by 90°
- B) Lag voltage by 90°
- C) Be in phase with voltage
- D) Have zero magnitude
Answer: B) Lag voltage by 90°
Explanation: Inductive reactance causes current to lag the applied voltage by 90 degrees.
- A pure capacitor in AC causes current to:
- A) Lead voltage by 90°
- B) Lag voltage by 90°
- C) Be in phase with voltage
- D) Be zero Answer: A) Lead voltage by 90° Explanation: Capacitive reactance makes current lead voltage by 90 degrees.
- The reactance of an inductor is:
- A) XL = 1/(2πfC)
- B) XL = 2πfL
- C) XL = R + jωL
- D) XL = 1/ωL Answer: B) XL = 2πfL Explanation: Inductive reactance increases linearly with frequency and inductance.
- The reactance of a capacitor is:
- A) XC = 2πfC
- B) XC = 1/(2πfC)
- C) XC = ωL
- D) XC = R/C
Answer: B) XC = 1/(2πfC)
Explanation: Capacitive reactance decreases with frequency and capacitance.
- In a series RLC circuit at resonance, the impedance is:
- A) Maximum
- B) Minimum and equal to R
- C) Purely inductive
- D) Purely capacitive Answer: B) Minimum and equal to R Explanation: At resonance, XL = XC, reactive parts cancel, leaving Z = R (minimum magnitude).
- The frequency at which a series RLC resonates is:
- A) f0 = 1/(2π√(LC))
- B) f0 = 1/(2πRC)
- C) f0 = R/(2πL)
- D) f0 = 2π√(LC) Answer: A) f0 = 1/(2π√(LC)) Explanation: Resonance occurs when ω0 = 1/√(LC), so f0 = ω0/(2π).
- Which is true for parallel resistors?
- A) Equivalent resistance is the sum
- B) Equivalent resistance is less than the smallest branch
- C) Equivalent resistance is greater than the largest branch
- D) Equivalent resistance equals the average Answer: B) Equivalent resistance is less than the smallest branch Explanation: Adding parallel paths increases conductance and reduces total resistance below any individual branch value.
- The drift velocity of electrons in a typical conductor under normal currents is:
- A) Approximately the speed of light
- B) Several meters per second
- C) Millimeters per second
- D) Zero
Answer: C) Millimeters per second
Explanation: Electron drift is very slow; signals propagate fast via the field, but individual electron drift speeds are small.
- The conductivity unit is:
- A) Ω·m
- B) S/m
- C) H/m
- D) F/m Answer: B) S/m Explanation: Conductivity σ is reciprocal of resistivity ρ (Ω·m); σ has units siemens per meter.
- Which equation relates electric force between point charges?
- A) Ampère’s Law
- B) Coulomb’s Law
- C) Faraday’s Law
- D) Gauss’s Law for magnetism Answer: B) Coulomb’s Law Explanation: Coulomb’s Law: F = k q1 q2 / r^2 along the line joining the charges, in electrostatics.
- Electric potential energy increases when:
- A) Like charges move closer
- B) Opposite charges move closer
- C) A resistor dissipates heat
- D) A capacitor discharges
Answer: A) Like charges move closer
Explanation: Work must be done to push like charges together, increasing potential energy. Opposite charges attract, reducing potential energy when closer.
- The internal resistance of an ideal voltage source is:
- A) Infinite
- B) Zero
- C) Equal to load resistance
- D) Frequency dependent Answer: B) Zero Explanation: An ideal voltage source maintains fixed voltage regardless of load, modeled with zero internal resistance.
- The internal resistance of an ideal current source is:
- A) Zero
- B) Infinite
- C) Equal to load resistance
- D) Negative Answer: B) Infinite Explanation: An ideal current source maintains fixed current independent of load, modeled with infinite internal resistance (open circuit in parallel model).
- The Thevenin equivalent of a linear circuit is:
- A) A current source in parallel with a resistor
- B) A voltage source in series with a resistor
- C) A dependent source only
- D) A capacitor in series with an inductor Answer: B) A voltage source in series with a resistor Explanation: Thevenin’s theorem replaces any two-terminal linear network with Vth in series with Rth as seen from the terminals.
- Norton’s theorem states that a linear circuit can be replaced by:
- A) A voltage source in series with a resistor
- B) A current source in parallel with a resistor
- C) A single resistor
- D) A dependent source only
Answer: B) A current source in parallel with a resistor
Explanation: Norton equivalent is In in parallel with Rn; Rn equals Rth and In = Vth/Rth.
- The unit of magnetic flux is:
- A) Tesla
- B) Weber
- C) Henry
- D) Gauss Answer: B) Weber Explanation: Magnetic flux Φ is measured in webers (Wb); flux density B in teslas (T).
- Faraday’s law of electromagnetic induction states that induced emf is proportional to:
- A) The change in current
- B) The rate of change of magnetic flux
- C) The absolute value of magnetic flux
- D) The square of magnetic field Answer: B) The rate of change of magnetic flux Explanation: ε = -dΦ/dt; the negative sign is Lenz’s law indicating opposing change.
- Lenz’s law indicates the direction of induced current such that it:
- A) Assists the change causing it
- B) Opposes the change causing it
- C) Is random
- D) Maximizes power transfer Answer: B) Opposes the change causing it Explanation: The induced current creates a field opposing the change in flux (energy conservation).
- For maximum power transfer from a Thevenin source to a resistive load, the load resistance should be:
- A) Zero
- B) Infinite
- C) Equal to Thevenin resistance
- D) Twice Thevenin resistance
Answer: C) Equal to Thevenin resistance
Explanation: Maximum power occurs when RL = Rth; then half the source voltage appears across RL and power is maximized.
- The temperature coefficient of resistance for most pure metals is:
- A) Negative
- B) Positive
- C) Zero
- D) Infinite Answer: B) Positive Explanation: Metal resistance increases with temperature due to increased lattice scattering of electrons.
- A fuse protects a circuit by:
- A) Blocking voltage spikes
- B) Storing charge
- C) Melting when current exceeds a limit
- D) Reducing power factor Answer: C) Melting when current exceeds a limit Explanation: Fuses are sacrificial overcurrent protection; excessive current heats the element until it opens the circuit.
- Grounding (earthing) primarily improves:
- A) Signal bandwidth
- B) Safety by providing a low-resistance fault path
- C) Battery life
- D) Motor speed
Answer: B) Safety by providing a low-resistance fault path
Explanation: Grounding ensures fault currents have a safe path, causing protective devices to trip and preventing shock hazards.
- The capacitance of a parallel-plate capacitor increases when:
- A) Plate area decreases
- B) Plate separation increases
- C) A dielectric with higher permittivity is inserted
- D) Temperature decreases Answer: C) A dielectric with higher permittivity is inserted Explanation: C = εA/d; increasing ε (relative permittivity) or area A, or decreasing separation d, increases capacitance.
- The RMS value of a 120 Vpeak sinusoidal voltage is approximately:
- A) 120 V
- B) 84.9 V
- C) 60 V
- D) 170 V
Answer: B) 84.9 V
Explanation: Vrms = Vpeak/√2 = 120/1.414 ≈ 84.9 V. Note: In North America, 120 V nominal mains is Vrms, corresponding to about 170 V peak.