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RBSE Sec Voc Electronics and Hardware study materials
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RBSE Sec Voc Electronics and Hardware practice questions

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Question 1Basic Electrical and Electronic Fundamentals

A resistor has color bands brown, black, red, gold. What is its nominal resistance and tolerance?

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

Explanation

Brown = 1, black = 0, red multiplier = ×100, giving 10 × 100 = 1000 Ω = 1 kΩ. The gold tolerance band means ±5%. Therefore the component is a 1 kΩ ±5% resistor.

Question 2Basic Electrical and Electronic Fundamentals

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

  1. Current leads the voltage by 90°
  2. Current is in phase with the voltage Correct answer.
  3. Current lags the voltage by 90°
  4. Current is in phase opposition, 180° apart

Explanation

A resistor has no reactance, so it cannot store or delay energy. Voltage across it and current through it reach their peaks and zero crossings at the same instant. Hence the phase difference is zero degrees.

Question 3Basic Electrical and Electronic Fundamentals

Which semiconductor material is most commonly used as the base for general-purpose bipolar and field-effect transistors in modern electronics?

  1. Selenium
  2. Gallium arsenide
  3. Silicon Correct answer.
  4. Germanium

Explanation

Silicon dominates because it forms a stable, abundant native oxide and tolerates high operating temperatures. Its refined crystal growth is well established, giving reliable, low-cost devices. Germanium and compound semiconductors are used only in specialised niches.

Question 4Basic Electrical and Electronic Fundamentals

A silicon diode is forward biased with a series resistor from a 5 V supply. Which value best approximates the voltage across the diode once it conducts?

  1. 5 V
  2. 0 V
  3. 0.7 V Correct answer.
  4. 1.4 V

Explanation

A forward-biased silicon PN junction drops about 0.6 to 0.7 V when conducting. The remainder of the supply voltage appears across the series resistor. This barrier voltage is the knee of the silicon diode characteristic.

Question 5Basic Electrical and Electronic Fundamentals

Which statement correctly describes the function of a capacitor in a DC power supply filter?

  1. It blocks DC while passing ripple current
  2. It converts AC to DC by rectification
  3. It stores charge and smooths the ripple voltage Correct answer.
  4. It regulates the output to a fixed value

Explanation

A filter capacitor charges near the peak of the rectified waveform and discharges through the load between peaks. This fills the gaps and reduces ripple amplitude. Rectification itself is performed by diodes, not the capacitor.

Question 6Basic Electrical and Electronic Fundamentals

What is the primary purpose of a fuse in an electrical circuit?

  1. To convert excess current into useful voltage
  2. To reduce the supply voltage to a safer level
  3. To limit the current to a fixed value during normal operation
  4. To open the circuit when current exceeds a safe value Correct answer.

Explanation

A fuse contains a calibrated element that melts when current exceeds its rating for a given time. This interrupts the circuit before conductors or components overheat. It protects against overload and short-circuit faults.

Question 7Basic Electrical and Electronic Fundamentals

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

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

Explanation

For two parallel resistors, the product over sum rule gives (6 × 3)/(6 + 3) = 18/9 = 2 Ω. The result must also be less than the smallest branch resistance, which 2 Ω satisfies.

Question 8Basic Electrical and Electronic Fundamentals

Which unit is used to express the capacitance of a capacitor?

  1. Weber
  2. Farad Correct answer.
  3. Ohm
  4. Henry

Explanation

Capacitance is charge stored per unit voltage, so one farad equals one coulomb per volt. The farad is the SI derived unit for this quantity. Practical components are usually rated in microfarads, nanofarads or picofarads.

Question 9Basic Electrical and Electronic Fundamentals

A 12 V supply feeds a 4 Ω resistor. What power is dissipated in the resistor?

  1. 48 W
  2. 3 W
  3. 0.33 W
  4. 36 W Correct answer.

Explanation

Power can be found as P = V²/R = 12²/4 = 144/4 = 36 W. Alternatively the current is 3 A, and P = VI = 12 × 3 = 36 W. Both methods agree.

Question 10Basic Electrical and Electronic Fundamentals

A Zener diode is to be used as a simple shunt voltage regulator. How must it be connected?

  1. Reverse biased in parallel with the load Correct answer.
  2. Forward biased in parallel with the load
  3. Reverse biased in series with the load
  4. Forward biased in series with the load

Explanation

Regulation uses the Zener breakdown region, which requires reverse bias. The diode is placed across the load so it clamps the voltage at its Zener value. A series resistor drops the excess supply voltage.

Question 11Basic Electrical and Electronic Fundamentals

In an NPN bipolar transistor operating in the active region, which relationship holds?

  1. The emitter current equals the base current minus the collector current
  2. The collector current is approximately beta times the base current Correct answer.
  3. The collector current is independent of base current
  4. The base current is larger than the collector current

Explanation

In the active region the base-emitter junction is forward biased and the base-collector junction reverse biased. A small base current controls a much larger collector current, with the ratio being the forward current gain beta. The emitter current is the sum of base and collector currents.

Question 12Basic Electrical and Electronic Fundamentals

What is the main advantage of a bridge rectifier over a centre-tap full-wave rectifier?

  1. It requires no transformer at all
  2. It needs only one diode
  3. It uses the whole transformer secondary, giving higher output for the same winding Correct answer.
  4. It produces a perfectly smooth DC output without filtering

Explanation

A bridge rectifier conducts on both half cycles using the full secondary voltage. The centre-tap circuit uses only half the winding at a time, so its peak output is roughly half. The bridge also avoids the need for a centre tap.

Question 13Basic Electrical and Electronic Fundamentals

An inductor of 0.5 H carries a steady current of 2 A. How much energy is stored in its magnetic field?

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

Explanation

Inductor energy is W = ½ L I². Substituting gives ½ × 0.5 × 2² = ½ × 0.5 × 4 = 1 J. The stored energy grows with the square of the current.

Question 14Basic Electrical and Electronic Fundamentals

What is the purpose of a bleeder resistor across a large filter capacitor in a power supply?

  1. To increase the output current rating
  2. To increase the ripple voltage
  3. To rectify the AC input
  4. To discharge the capacitor after power is removed for safety Correct answer.

Explanation

A large capacitor can retain a dangerous charge long after the supply is switched off. A high-value bleeder resistor provides a discharge path so the voltage falls to a safe level. It also slightly improves regulation by maintaining a minimum load.

Question 15Basic Electrical and Electronic Fundamentals

A coil has an inductive reactance of 30 Ω and a resistance of 40 Ω at a given frequency. What is its impedance?

  1. 50 Ω Correct answer.
  2. 10 Ω
  3. 70 Ω
  4. 1200 Ω

Explanation

Resistance and reactance are 90° out of phase, so they combine as the phasor sum Z = √(R² + X²). Here √(40² + 30²) = √(1600 + 900) = √2500 = 50 Ω. This is the familiar 3-4-5 triangle scaled by ten.

Question 16Basic Electrical and Electronic Fundamentals

Which statement about a P-type semiconductor is correct?

  1. Its majority carriers are holes created by acceptor doping Correct answer.
  2. It conducts only when illuminated
  3. Its majority carriers are electrons
  4. It is negatively charged overall

Explanation

Adding trivalent acceptor atoms such as boron creates vacancies in the covalent bonds, called holes. These holes behave as mobile positive charge carriers. The material remains electrically neutral because each acceptor atom is itself neutral.

Question 17Basic Electrical and Electronic Fundamentals

A transformer has 400 turns on the primary and 100 turns on the secondary. If the primary is connected to 230 V AC, what is the secondary voltage approximately?

  1. 57.5 V Correct answer.
  2. 115 V
  3. 230 V
  4. 920 V

Explanation

The turns ratio is 400:100, or 4:1. Secondary voltage equals primary voltage multiplied by the ratio of secondary to primary turns: 230 × (100/400) = 57.5 V. This is a step-down transformer.

Question 18Basic Electrical and Electronic Fundamentals

Which of these describes the key property of a material used for a varistor (voltage-dependent resistor)?

  1. Its resistance falls sharply when the applied voltage exceeds a threshold Correct answer.
  2. Its capacitance varies with frequency
  3. Its resistance is fixed by its physical length
  4. Its resistance rises steadily with temperature

Explanation

A metal-oxide varistor has a highly non-linear characteristic that clamps transient overvoltages. Below the threshold it presents high resistance; above it, resistance drops and the surge is diverted. This protects equipment from voltage spikes.

Question 19Basic Electrical and Electronic Fundamentals

A 9 V battery is connected across a series combination of a 1 kΩ resistor and a red LED with a forward drop of 2 V. What current flows?

  1. 11 mA
  2. 9 mA
  3. 2 mA
  4. 7 mA Correct answer.

Explanation

The resistor must drop the difference between supply and LED voltage, 9 − 2 = 7 V. Using Ohm's law, I = 7 V / 1000 Ω = 7 mA. The LED's forward drop must be subtracted before applying Ohm's law.

Question 20Basic Electrical and Electronic Fundamentals

What happens to the total capacitance when two capacitors are connected in parallel?

  1. It is unchanged regardless of connection
  2. It equals the sum of the individual capacitances Correct answer.
  3. It is less than the smallest capacitance
  4. It equals the reciprocal of the sum of reciprocals

Explanation

In parallel, each capacitor sees the same voltage and their stored charges add. Since Q = CV, the effective capacitance is the direct sum. This is the opposite of the resistor rule for parallel connection.

Question 21Basic Electrical and Electronic Fundamentals

Which statement best explains why a bipolar transistor dissipates power even when it is switching a load?

  1. The collector is always at zero volts
  2. The base-emitter junction is always reverse biased
  3. During transitions it passes current while a voltage is developed across it Correct answer.
  4. The transistor stores charge in an external coil

Explanation

Instantaneous power is the product of collector current and collector-emitter voltage. During switching, neither is zero, so heat is generated. Fast switching and good drive reduce the time spent in this high-loss region.

Question 22Basic Electrical and Electronic Fundamentals

A wire of resistivity ρ, length L and cross-sectional area A has resistance R. If the length is doubled and the area is halved while material stays the same, what is the new resistance?

  1. 2R
  2. R
  3. 4R Correct answer.
  4. R/2

Explanation

Resistance is given by R = ρL/A. Doubling L doubles R, and halving A doubles it again. The combined effect is a fourfold increase, giving 4R.

Question 23Basic Electrical and Electronic Fundamentals

In a series RLC circuit at resonance, which condition is true?

  1. The phase angle between voltage and current is 90°
  2. The inductive and capacitive reactances are equal and cancel Correct answer.
  3. The current is at its minimum
  4. The impedance is at its maximum

Explanation

At resonance XL equals XC, so the two reactive voltages cancel. The circuit then behaves as pure resistance, giving minimum impedance and maximum current. The phase angle is zero because the net reactance is zero.

Question 24Basic Electrical and Electronic Fundamentals

A common-emitter amplifier with a bypassed emitter resistor shows a voltage gain of about 150 but a very wide bandwidth. If the emitter bypass capacitor is removed, what happens?

  1. Gain and bandwidth both remain unchanged
  2. Gain rises and bandwidth widens
  3. Gain falls and bandwidth narrows
  4. Gain falls but bandwidth widens Correct answer.

Explanation

Removing the bypass introduces unbypassed emitter resistance, which provides negative feedback. This reduces voltage gain but extends the bandwidth and improves linearity. The gain-bandwidth product remains roughly constant.

Question 25Basic Electrical and Electronic Fundamentals

A 10-bit ADC has a full-scale input range of 0 to 5.12 V. What is the approximate resolution (smallest detectable voltage step)?

  1. 10 mV
  2. 20 mV
  3. 5 mV Correct answer.
  4. 2.5 mV

Explanation

A 10-bit converter has 2^10 = 1024 steps. Dividing 5.12 V by 1024 gives 0.005 V, or 5 mV per step. This step size is the quantisation resolution of the converter.

Question 26Basic Electrical and Electronic Fundamentals

In a household wiring circuit, which conductor is intentionally connected to earth potential so that exposed metal enclosures remain at zero volts under normal conditions?

  1. The live (phase) conductor
  2. The switched live conductor
  3. The neutral conductor
  4. The earth (ground) conductor Correct answer.

Explanation

The earth conductor is bonded to the general mass of earth and to exposed metalwork, so it holds those surfaces at earth potential and carries fault current back to trip the protective device. It normally carries no current, unlike the neutral, which is the return path for the load current.

Question 27Basic Electrical and Electronic Fundamentals

A carbon resistor is marked brown, black, red, gold. What is its nominal resistance and tolerance?

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

Explanation

Reading the four bands: brown = 1, black = 0, red = multiplier 10², gold = ±5%. This gives 10 × 100 Ω = 1000 Ω, i.e. 1 kΩ with 5% tolerance.

Question 28Basic Electrical and Electronic Fundamentals

A silicon diode and a 220 Ω resistor are connected in series across a 5 V DC supply, with the diode forward biased. Taking the diode forward drop as 0.7 V, what current flows?

  1. About 19.5 mA Correct answer.
  2. About 26.0 mA
  3. About 2.3 mA
  4. About 22.7 mA

Explanation

Kirchhoff's voltage law gives the resistor voltage as 5 V − 0.7 V = 4.3 V. Ohm's law then gives I = 4.3 V / 220 Ω ≈ 0.0195 A, or about 19.5 mA.

Question 29Basic Electrical and Electronic Fundamentals

An ideal op-amp is configured as a non-inverting amplifier with a 10 kΩ feedback resistor and a 2.2 kΩ resistor from the inverting input to ground. What is the closed-loop voltage gain?

  1. About 4.5
  2. About 0.18
  3. About 5.5 Correct answer.
  4. About 10

Explanation

For the non-inverting configuration the gain is 1 + Rf/Rin = 1 + 10/2.2 ≈ 1 + 4.55 ≈ 5.5. The input signal is applied to the non-inverting terminal, so the output is in phase with the input.

Question 30Basic Electrical and Electronic Fundamentals

A coil with resistance 8 Ω and inductive reactance 6 Ω is connected to a 10 V AC source. Which statement about the circuit is correct?

  1. The impedance is 10 Ω, the current is 1 A, and the current lags the applied voltage by about 37° Correct answer.
  2. The impedance is 2 Ω and the current is 5 A
  3. The impedance is 14 Ω and the current is about 0.71 A
  4. The impedance is 10 Ω, the current is 1 A, and the current leads the voltage by about 37°

Explanation

Impedance magnitude is √(R² + XL²) = √(64 + 36) = 10 Ω, so I = 10 V / 10 Ω = 1 A. The phase angle is arctan(XL/R) = arctan(0.75) ≈ 37°, and in an inductive circuit the current lags the voltage by that angle.

Question 31Electronic Components and Passive Devices

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

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

Explanation

In the four-band code the first two bands give significant digits (brown = 1, black = 0) and the third band gives the multiplier (red = ×100), so the value is 10 × 100 = 1000 Ω = 1 kΩ. The fourth band sets tolerance, and gold means ±5%. Silver would instead indicate ±10%.

Question 32Electronic Components and Passive Devices

Which statement correctly describes the behaviour of a capacitor in a DC circuit once steady state is reached?

  1. It behaves as a constant-current source
  2. It behaves as an open circuit and blocks steady current Correct answer.
  3. It behaves as a fixed voltage source
  4. It behaves as a short circuit and passes steady current

Explanation

A capacitor stores charge on two plates separated by a dielectric, so no sustained conduction path exists through it. After the charging transient ends, the current falls to zero and the capacitor looks like an open circuit at DC. Its steady-state voltage equals the voltage of the source it charged from.

Question 33Electronic Components and Passive Devices

A transformer is required to step 230 V AC down to 23 V AC. What turns ratio (primary : secondary) achieves this?

  1. 23 : 10
  2. 1 : 10
  3. 10 : 1 Correct answer.
  4. 1 : 23

Explanation

For an ideal transformer the voltage ratio equals the turns ratio, so Vp/Vs = Np/Ns. Here 230/23 = 10, meaning ten primary turns are needed for every secondary turn. The ratio is therefore written 10 : 1, a step-down configuration.

Question 34Electronic Components and Passive Devices

Two resistors of 100 Ω and 150 Ω are connected in parallel. What is the equivalent resistance?

  1. 60 Ω Correct answer.
  2. 75 Ω
  3. 125 Ω
  4. 250 Ω

Explanation

For two resistors in parallel, Rp = (R1 × R2)/(R1 + R2) = (100 × 150)/(250) = 15000/250 = 60 Ω. The result must always be smaller than the smallest branch resistor, which confirms 60 Ω is sensible.

Question 35Electronic Components and Passive Devices

Which property makes an inductor oppose a change in current through it?

  1. It dissipates energy as heat in proportion to frequency
  2. It converts the current directly into a voltage by chemical action
  3. It stores energy in a magnetic field that collapses when current changes Correct answer.
  4. It stores energy in an electrostatic field between its turns

Explanation

Current through a coil establishes a magnetic field, and energy is stored in that field. When the current tries to change, the collapsing or expanding field induces a back EMF that opposes the change, giving the inductor its characteristic inertia. This is described by v = L di/dt.

Question 36Electronic Components and Passive Devices

A diode is forward biased in a circuit with a series resistor. Which description matches its typical silicon behaviour?

  1. It behaves as a pure resistor of about 0.7 Ω
  2. It conducts heavily in reverse and blocks in forward bias
  3. It drops about 0.7 V in both directions equally
  4. It drops about 0.7 V when conducting and blocks reverse current Correct answer.

Explanation

A silicon PN junction needs roughly 0.6 to 0.7 V of forward voltage before it conducts appreciably, after which it holds approximately that drop. In reverse bias the depletion region widens and only a tiny leakage current flows. This one-way conduction is the basis of rectification.

Question 37Electronic Components and Passive Devices

Which capacitor type is normally chosen for a high-value, low-cost coupling application where polarity is not a concern?

  1. Polystyrene film capacitor
  2. Aluminium electrolytic capacitor Correct answer.
  3. Ceramic disc capacitor
  4. Silver mica capacitor

Explanation

Aluminium electrolytic capacitors pack large capacitance into a small, inexpensive package, which suits coupling and smoothing roles. They are polarised, so the designer must keep the positive terminal at the higher potential. Where polarity is genuinely irrelevant, a non-polarised type would be substituted.

Question 38Electronic Components and Passive Devices

A resistor dissipates 2 W and carries 100 mA. What is its resistance?

  1. 200 Ω Correct answer.
  2. 50 Ω
  3. 2 kΩ
  4. 20 Ω

Explanation

Using P = I²R, rearrange to R = P/I² = 2/(0.1)² = 2/0.01 = 200 Ω. Converting milliamps to amps before squaring is essential, since using 100 directly would give a wildly wrong answer. The resistor should also be rated comfortably above 2 W for reliability.

Question 39Electronic Components and Passive Devices

What is the main purpose of a Zener diode in a power supply circuit?

  1. To store charge for smoothing
  2. To amplify small signal voltages
  3. To provide a stable reference voltage by operating in reverse breakdown Correct answer.
  4. To rectify alternating current into direct current

Explanation

A Zener diode is designed to operate safely in reverse breakdown, where its voltage stays nearly constant over a range of currents. This makes it useful as a shunt voltage reference or simple regulator. Ordinary rectification is the job of a standard PN diode.

Question 40Electronic Components and Passive Devices

A capacitor of 10 µF is charged to 50 V. How much energy does it store?

  1. 0.025 J
  2. 0.0125 J Correct answer.
  3. 0.5 J
  4. 2.5 J

Explanation

Energy stored in a capacitor is E = ½CV². Substituting C = 10 × 10⁻⁶ F and V = 50 V gives E = 0.5 × 10⁻⁵ × 2500 = 0.0125 J. Forgetting the half factor is the most common error and doubles the result.

Question 41Electronic Components and Passive Devices

Which statement about the temperature coefficient of a resistor is correct?

  1. The coefficient only applies to wirewound types
  2. A positive coefficient means resistance rises as temperature rises Correct answer.
  3. A positive coefficient means resistance falls as temperature rises
  4. The coefficient is independent of the resistive material

Explanation

The temperature coefficient expresses how much resistance changes per degree of temperature change. A positive value means resistance increases with temperature, which is typical of metals such as copper. A negative value, common in carbon composition and thermistors, means resistance falls as temperature rises.

Question 42Electronic Components and Passive Devices

In a bridge rectifier fed from a transformer, what is the approximate peak inverse voltage that each diode must withstand?

  1. Half the peak secondary voltage
  2. Equal to the RMS secondary voltage
  3. Twice the peak secondary voltage
  4. Equal to the peak secondary voltage Correct answer.

Explanation

In a full-wave bridge, two diodes conduct on each half cycle while the other two are reverse biased. The reverse voltage across an off diode reaches approximately the peak secondary voltage, so diodes rated above that peak are selected. A centre-tapped full-wave rectifier instead imposes about twice the peak per diode.

Question 43Electronic Components and Passive Devices

Which effect explains why a real capacitor passes a small current even after long charging at DC?

  1. Piezoelectric resonance
  2. Leakage current through the dielectric Correct answer.
  3. Equivalent series inductance
  4. Dielectric absorption

Explanation

No dielectric is a perfect insulator, so a small leakage current flows continuously through it under applied voltage. This leakage is modelled as a large resistance in parallel with the ideal capacitance. Dielectric absorption concerns charge retention after discharge, not steady conduction.

Question 44Electronic Components and Passive Devices

What happens to the total capacitance when two identical capacitors are connected in series?

  1. It stays the same
  2. It halves Correct answer.
  3. It doubles
  4. It becomes zero

Explanation

Capacitors in series combine like resistors in parallel: 1/Ctotal = 1/C1 + 1/C2. For two equal values C, the result is C/2, so the total halves. The voltage rating of the combination, however, increases.

Question 45Electronic Components and Passive Devices

A relay coil rated 12 V, 60 mA is to be driven from a 12 V supply through a series resistor to reduce coil current to 40 mA. What series resistance is needed, assuming the coil resistance stays constant?

  1. 200 Ω
  2. 300 Ω
  3. 60 Ω
  4. 100 Ω Correct answer.

Explanation

Coil resistance is 12 V / 60 mA = 200 Ω. For 40 mA total, the loop resistance must be 12 V / 40 mA = 300 Ω, so the added series resistor is 300 − 200 = 100 Ω. The resistor must also be rated for I²R = 0.16 W, so a ½ W part is appropriate.

Question 46Electronic Components and Passive Devices

Which material is most commonly used as the dielectric in a general-purpose ceramic capacitor?

  1. Mylar polyester film
  2. Barium titanate Correct answer.
  3. Sulphur hexafluoride gas
  4. Aluminium oxide

Explanation

Barium titanate has a very high permittivity, which allows ceramic capacitors to achieve large capacitance in small packages. Its properties vary with temperature and voltage, which is why ceramic types are specified by class. Polyester film and aluminium oxide belong to other capacitor families.

Question 47Electronic Components and Passive Devices

A varistor is placed across the mains input of a power supply. What is its function?

  1. To provide a stable reference for the regulator
  2. To smooth the rectified DC output
  3. To clamp voltage transients and protect downstream components Correct answer.
  4. To limit inrush current at switch-on

Explanation

A metal oxide varistor has a non-linear resistance that falls sharply above a threshold voltage, diverting surge energy away from the circuit. It therefore clamps transient overvoltages such as spikes on the mains. It does not operate continuously in normal conditions.

Question 48Electronic Components and Passive Devices

Which statement best explains why an electrolytic capacitor must not be reverse biased?

  1. Its capacitance would increase without limit
  2. Its equivalent series resistance would fall to zero
  3. The oxide layer can break down and the capacitor may vent or fail Correct answer.
  4. It would start behaving as an inductor

Explanation

The anodised oxide film in an electrolytic capacitor is formed to withstand voltage in one direction only. Applying reverse voltage electrochemically erodes that film, causing high current, gas generation, and possible rupture. Correct polarity must therefore be observed during assembly.

Question 49Electronic Components and Passive Devices

An inductor of 10 mH carries a steady current of 2 A. What energy is stored in its magnetic field?

  1. 0.2 J
  2. 0.01 J
  3. 0.04 J
  4. 0.02 J Correct answer.

Explanation

Energy in an inductor is E = ½LI². Substituting L = 10 × 10⁻³ H and I = 2 A gives E = 0.5 × 0.01 × 4 = 0.02 J. The half factor arises because the current builds up gradually against the induced back EMF.

Question 50Electronic Components and Passive Devices

Why is a ferrite core often inserted into an inductor used in a switched-mode power supply?

  1. To raise the inductance for a given number of turns and confine the field Correct answer.
  2. To eliminate all core losses at high frequency
  3. To make the inductor behave as a capacitor at high frequency
  4. To reduce the saturation flux density of the winding

Explanation

A high-permeability core concentrates magnetic flux, so a much higher inductance is obtained from fewer turns. Ferrite is chosen for high-frequency work because its losses are lower than laminated steel at those frequencies. Core losses are reduced but never eliminated entirely.