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Karnataka KSEAB SSLC NSQF Electronics and Hardware study materials
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Karnataka KSEAB SSLC NSQF Electronics and Hardware practice questions

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Question 1Basic Electrical and Electronic Fundamentals

In a closed circuit, a resistor of 12 Ω carries a current of 0.5 A. What is the potential difference across the resistor?

  1. 6 V Correct answer.
  2. 0.042 V
  3. 12.5 V
  4. 24 V

Explanation

Ohm's law states that V = I × R, so the voltage equals 0.5 A multiplied by 12 Ω, which gives 6 V. The multiplication must use the current in amperes and resistance in ohms to yield volts.

Question 2Basic Electrical and Electronic Fundamentals

Which quantity is measured in coulombs in an electric circuit?

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

Explanation

The coulomb is the SI unit of electric charge, defined as the charge transported by one ampere flowing for one second. Other electrical quantities use different units, such as the volt, ohm, and watt.

Question 3Basic Electrical and Electronic Fundamentals

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

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

Explanation

For two resistors in parallel, the equivalent resistance is the product divided by the sum, so (6 × 3) ÷ (6 + 3) equals 18 ÷ 9, which is 2 Ω. The result must be smaller than the smallest branch resistance, confirming the calculation.

Question 4Basic Electrical and Electronic Fundamentals

A battery of 9 V is connected to a resistor and the current measured is 3 mA. What is the resistance?

  1. 3 kΩ Correct answer.
  2. 27 kΩ
  3. 27 Ω
  4. 333 Ω

Explanation

Rearranging Ohm's law gives R = V ÷ I, so 9 V divided by 0.003 A equals 3000 Ω, which is 3 kΩ. The current must first be converted from milliamperes to amperes before dividing.

Question 5Basic Electrical and Electronic Fundamentals

Which material is classified as a semiconductor at room temperature?

  1. Rubber
  2. Copper
  3. Silicon Correct answer.
  4. Mica

Explanation

Silicon has four valence electrons and a conductivity between that of conductors and insulators, making it a semiconductor. Its conductivity rises when doped or heated, unlike metals and insulators.

Question 6Basic Electrical and Electronic Fundamentals

In a pure silicon crystal at absolute zero, what is the state of the valence electrons?

  1. They are free to move through the lattice
  2. They are all locked in covalent bonds Correct answer.
  3. They are donated by impurity atoms
  4. They form a conduction band only

Explanation

At absolute zero an intrinsic semiconductor has no thermal energy to break covalent bonds, so every valence electron remains bound in a covalent bond. No free electrons or holes exist, and the crystal behaves as an insulator.

Question 7Basic Electrical and Electronic Fundamentals

A p-type semiconductor is formed by adding which type of impurity to silicon?

  1. A pentavalent element such as phosphorus
  2. A monovalent element such as sodium
  3. A tetravalent element such as carbon
  4. A trivalent element such as boron Correct answer.

Explanation

Trivalent atoms such as boron have only three valence electrons, so one bond remains incomplete and creates a hole. These impurities are called acceptors and make the material p-type, where holes are the majority carriers.

Question 8Basic Electrical and Electronic Fundamentals

In the depletion region of an unbiased p-n junction, what is the dominant condition?

  1. A built-in electric field opposes diffusion Correct answer.
  2. Only minority carriers exist in the bulk
  3. A large forward current flows
  4. The region has zero resistance

Explanation

Diffusion of carriers across the junction leaves behind fixed ionised atoms that create a built-in electric field. This field opposes further diffusion until an equilibrium barrier is established.

Question 9Basic Electrical and Electronic Fundamentals

A silicon diode is forward biased with a series resistor. Which value is closest to its typical barrier voltage?

  1. 1.5 V
  2. 0.7 V Correct answer.
  3. 5 V
  4. 0.3 V

Explanation

A forward-biased silicon diode begins to conduct appreciably at about 0.7 V, which is the barrier potential of the junction. This value is used when calculating the current in a diode circuit.

Question 10Basic Electrical and Electronic Fundamentals

In a half-wave rectifier using one diode, what is the ripple frequency when the input is a 50 Hz AC supply?

  1. 25 Hz
  2. 50 Hz Correct answer.
  3. 100 Hz
  4. 150 Hz

Explanation

A half-wave rectifier passes only one half of each input cycle, so the output pulses occur once per input cycle. The ripple frequency therefore equals the input frequency of 50 Hz.

Question 11Basic Electrical and Electronic Fundamentals

Which component is connected in parallel with the load to reduce ripple in a simple DC power supply?

  1. A fuse
  2. A zener diode in reverse breakdown
  3. A filter capacitor Correct answer.
  4. A series resistor

Explanation

A large capacitor connected across the load charges during each pulse and discharges between pulses, smoothing the output voltage. Its reactance falls as ripple frequency rises, so it bypasses the AC ripple.

Question 12Basic Electrical and Electronic Fundamentals

A zener diode is used as a voltage regulator. In which operating condition does it maintain a nearly constant voltage?

  1. Forward biased with a large current
  2. Reverse biased in the breakdown region Correct answer.
  3. Unbiased with no current
  4. Forward biased below 0.7 V

Explanation

When reverse biased beyond its breakdown voltage, a zener diode holds a nearly constant voltage across itself while the current varies within safe limits. The series resistor limits the current so the diode is not damaged.

Question 13Basic Electrical and Electronic Fundamentals

In an NPN transistor operating in the active region, which statement about current is correct?

  1. The collector current flows into the base
  2. The emitter current is smaller than the base current
  3. The collector current is much larger than the base current Correct answer.
  4. The base current equals the collector current

Explanation

In the active region the collector current is beta times the base current, so the collector current is much larger than the base current. The emitter current is the sum of the base and collector currents.

Question 14Basic Electrical and Electronic Fundamentals

An NPN transistor has a base current of 20 µA and a collector current of 2 mA. What is its current gain beta?

  1. 100 Correct answer.
  2. 10
  3. 40
  4. 200

Explanation

Beta equals collector current divided by base current, so 2 mA divided by 20 µA equals 100. Both currents must be expressed in the same unit before dividing.

Question 15Basic Electrical and Electronic Fundamentals

Which transistor configuration provides voltage gain with the output taken at the collector and the input at the base?

  1. Common emitter Correct answer.
  2. Common collector
  3. Common base
  4. Common gate

Explanation

In the common-emitter configuration the emitter is shared, the base is the input and the collector is the output, giving both voltage and current gain. It also inverts the signal, which is a characteristic feature of this configuration.

Question 16Basic Electrical and Electronic Fundamentals

Which logic gate outputs HIGH only when all its inputs are HIGH?

  1. AND gate Correct answer.
  2. NOR gate
  3. XOR gate
  4. OR gate

Explanation

The AND gate produces a HIGH output only when every input is HIGH; a single LOW input forces the output LOW. This behaviour follows the Boolean multiplication of the inputs.

Question 17Basic Electrical and Electronic Fundamentals

A two-input NAND gate receives inputs A = 1 and B = 1. What is the output?

  1. Undefined
  2. 1
  3. Equal to A only
  4. 0 Correct answer.

Explanation

The NAND gate is the inverse of AND, so with both inputs HIGH the AND result would be 1 and the NAND output is 0. This is the only condition that produces a LOW output from a NAND gate.

Question 18Basic Electrical and Electronic Fundamentals

Which Boolean expression represents the output of an exclusive-OR gate with inputs A and B?

  1. A′B + AB′ Correct answer.
  2. A · B
  3. A + B
  4. A′ + B′

Explanation

XOR is true when exactly one input is true, which is written as A′B + AB′. The first term covers A low and B high, while the second covers A high and B low.

Question 19Basic Electrical and Electronic Fundamentals

Using De Morgan's theorem, which expression is equivalent to (A + B)′?

  1. A · B
  2. A′ + B′
  3. A + B
  4. A′ · B′ Correct answer.

Explanation

De Morgan's theorem states that the complement of a sum equals the product of the complements, so (A + B)′ becomes A′ · B′. This converts a NOR operation into an AND of inverted inputs.

Question 20Basic Electrical and Electronic Fundamentals

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

  1. 10 kΩ
  2. 10 Ω
  3. 100 Ω
  4. 1 kΩ Correct answer.

Explanation

Brown is 1, black is 0, and red is a multiplier of 100, giving 10 × 100 = 1000 Ω, or 1 kΩ. The gold band indicates a tolerance of plus or minus five percent.

Question 21Basic Electrical and Electronic Fundamentals

Which property of a capacitor is described by its capacitance?

  1. Its resistance to direct current
  2. Its ability to store electric charge per unit voltage Correct answer.
  3. Its ability to dissipate heat
  4. Its magnetic flux linkage

Explanation

Capacitance is defined as the charge stored divided by the voltage across the plates, so C = Q ÷ V. It is measured in farads and depends on plate area, spacing and dielectric material.

Question 22Basic Electrical and Electronic Fundamentals

Three capacitors of 6 µF each are connected in series. What is the total capacitance?

  1. 6 µF
  2. 3 µF
  3. 18 µF
  4. 2 µF Correct answer.

Explanation

For capacitors in series, the reciprocals add, so 1/C = 1/6 + 1/6 + 1/6 = 3/6, giving C = 2 µF. The total is always smaller than the smallest individual capacitor.

Question 23Basic Electrical and Electronic Fundamentals

Which effect is the basis of operation of an inductor?

  1. Electrostatic attraction between plates
  2. Thermoelectric voltage between metals
  3. Self-induction producing an opposing EMF when current changes Correct answer.
  4. Photoelectric emission from a junction

Explanation

A changing current in a coil produces a changing magnetic flux, which induces an EMF that opposes the change according to Lenz's law. This property is called self-inductance and is measured in henries.

Question 24Basic Electrical and Electronic Fundamentals

A transformer steps down 240 V AC to 12 V AC. If the primary has 1200 turns, how many turns does the secondary have?

  1. 60 Correct answer.
  2. 100
  3. 240
  4. 120

Explanation

The turns ratio equals the voltage ratio, so secondary turns equal primary turns multiplied by secondary voltage divided by primary voltage. That gives 1200 × 12 ÷ 240, which equals 60 turns.

Question 25Basic Electrical and Electronic Fundamentals

A 100 W lamp operates on a 200 V supply. What current does it draw?

  1. 20 A
  2. 0.2 A
  3. 2 A
  4. 0.5 A Correct answer.

Explanation

Electrical power equals voltage multiplied by current, so current equals power divided by voltage. Dividing 100 W by 200 V gives 0.5 A.

Question 26Basic Electrical and Electronic Fundamentals

A copper wire of length 2 m has a resistance of 8 Ω. A second wire of the same material and same cross-sectional area has a length of 5 m. What is the resistance of the second wire?

  1. 20 Ω Correct answer.
  2. 3.2 Ω
  3. 16 Ω
  4. 40 Ω

Explanation

For a conductor of fixed material and fixed cross-section, resistance is directly proportional to length (R = ρL/A). Doubling the length doubles the resistance, so the ratio of resistances equals the ratio of lengths: 8 Ω × (5/2) = 20 Ω.

Question 27Basic Electrical and Electronic Fundamentals

In a household wiring circuit, a 60 W lamp and a 100 W lamp are connected in parallel across the same 230 V supply. Which statement about them is correct?

  1. Both lamps draw equal currents because they share the same supply voltage
  2. The 60 W lamp has the lower resistance and dissipates more power
  3. The 100 W lamp has the lower resistance and draws the larger current Correct answer.
  4. The 60 W lamp draws the larger current because its resistance is higher

Explanation

In a parallel connection both lamps see the full supply voltage, so power is P = V²/R. The higher-power lamp therefore has the smaller resistance, and since I = P/V it also draws the greater current.

Question 28Basic Electrical and Electronic Fundamentals

Which instrument is connected in series with a circuit branch to measure the current flowing through that branch?

  1. Voltmeter
  2. Ammeter Correct answer.
  3. Ohmmeter
  4. Potentiometer

Explanation

An ammeter must carry the branch current, so it is placed in series and designed to have very low resistance to avoid disturbing the circuit. A voltmeter instead goes in parallel across a component to sense potential difference.

Question 29Basic Electrical and Electronic Fundamentals

A resistor carries a current of 0.5 A when a potential difference of 10 V is applied across it. What power is dissipated in the resistor?

  1. 0.05 W
  2. 10 W
  3. 5 W Correct answer.
  4. 20 W

Explanation

Electrical power can be found from P = V × I, giving 10 V × 0.5 A = 5 W. The same result follows from P = I²R with R = V/I = 20 Ω.

Question 30Basic Electrical and Electronic Fundamentals

A coil of wire is wound on an iron core and a steady direct current flows through it. The current is then increased steadily at a constant rate. What happens to the induced emf in the coil during the increase?

  1. No emf is induced because the coil carries direct current
  2. An emf is induced only at the instant the current begins to change
  3. A constant emf is induced that aids the increase in current
  4. A constant emf is induced that opposes the increase in current Correct answer.

Explanation

Faraday's law gives induced emf proportional to the rate of change of flux linkage, so a steady rate of current change produces a steady emf. By Lenz's law this self-induced emf opposes the change that created it, so it acts against the rising current.

Question 31Electronic Components and Devices

In an NSQF electronics workshop, a student needs a fixed resistor whose value is read by colour bands. Which component is designed specifically to oppose current by a fixed amount in a circuit?

  1. Resistor Correct answer.
  2. Inductor
  3. Diode
  4. Capacitor

Explanation

A resistor is a passive component whose main function is to limit or oppose the flow of current by a fixed amount determined by its resistance value. Capacitors store charge, inductors store energy in a magnetic field, and diodes allow current mainly in one direction.

Question 32Electronic Components and Devices

A ceramic capacitor is marked 104. What is its capacitance?

  1. 0.104 µF
  2. 10 nF
  3. 100 nF Correct answer.
  4. 104 pF

Explanation

For three-digit capacitor codes the first two digits give the significant figures and the third digit gives the number of zeros in picofarads. Thus 104 means 10 followed by four zeros, i.e. 100000 pF, which equals 100 nF or 0.1 µF.

Question 33Electronic Components and Devices

Which property of a diode is used when it is connected as a rectifier in a power supply?

  1. It conducts easily in forward bias and blocks in reverse bias Correct answer.
  2. It stores charge like a capacitor
  3. It produces a constant voltage regardless of current
  4. It amplifies the input signal

Explanation

A rectifier relies on the diode's one-way conduction: it conducts when the anode is positive with respect to the cathode and blocks the reverse half of the AC cycle. This unidirectional property converts alternating current into pulsating direct current.

Question 34Electronic Components and Devices

Which material is a semiconductor commonly used to make general-purpose diodes and transistors in the electronics lab?

  1. Silicon Correct answer.
  2. Copper
  3. Nichrome
  4. Mica

Explanation

Silicon is the most widely used semiconductor because its conductivity can be controlled precisely by doping. Copper is a conductor, mica is an insulator, and nichrome is a resistance alloy.

Question 35Electronic Components and Devices

A transformer in a power supply steps 230 V AC down to 12 V AC. Which statement describes the action of this transformer?

  1. It changes AC voltage level by mutual induction Correct answer.
  2. It stores energy permanently for later use
  3. It increases the frequency of the supply
  4. It converts AC to DC directly

Explanation

A transformer transfers energy between two coils by mutual induction and changes the voltage level according to the turns ratio, without altering frequency. It works only with alternating current and does not rectify or store energy permanently.

Question 36Electronic Components and Devices

Which component is used in a circuit to store energy in an electric field between two conducting plates?

  1. Resistor
  2. Zener diode
  3. Inductor
  4. Capacitor Correct answer.

Explanation

A capacitor consists of two conducting plates separated by a dielectric and stores energy in the electric field when charged. Resistors dissipate energy, inductors store it magnetically, and zener diodes regulate voltage.

Question 37Electronic Components and Devices

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

  1. 100 Ω ±10%
  2. 10000 Ω ±5%
  3. 10 Ω ±5%
  4. 1000 Ω ±5% Correct answer.

Explanation

Brown is 1, black is 0, and red is a multiplier of 100, giving 10 × 100 = 1000 Ω. Gold in the fourth band indicates a tolerance of ±5%.

Question 38Electronic Components and Devices

Which device is a three-terminal semiconductor component used mainly to amplify or switch electronic signals?

  1. Varactor
  2. Bipolar junction transistor Correct answer.
  3. Fuse
  4. Light-emitting diode

Explanation

A bipolar junction transistor has three terminals (emitter, base, collector) and is used for amplification and switching. LEDs emit light, varactors act as voltage-controlled capacitors, and fuses protect against overcurrent.

Question 39Electronic Components and Devices

A 12 V supply is connected across two resistors of 4 Ω and 6 Ω in series. What current flows through the circuit?

  1. 5.0 A
  2. 0.5 A
  3. 1.2 A Correct answer.
  4. 2.0 A

Explanation

In series the resistances add, so the total is 4 + 6 = 10 Ω. Using Ohm's law, I = V/R = 12/10 = 1.2 A, and the same current flows through both resistors.

Question 40Electronic Components and Devices

Two resistors of 6 Ω and 3 Ω are connected in parallel across a 6 V supply. What is the total current drawn from the supply?

  1. 3.0 A Correct answer.
  2. 1.0 A
  3. 2.0 A
  4. 4.5 A

Explanation

The parallel equivalent resistance is (6 × 3)/(6 + 3) = 2 Ω. The total current is I = V/R = 6/2 = 3.0 A, which also equals the sum of branch currents 1 A and 2 A.

Question 41Electronic Components and Devices

An LED is to be operated from a 9 V battery with a forward voltage of 2 V and a forward current of 20 mA. What series resistor is required?

  1. 550 Ω
  2. 350 Ω Correct answer.
  3. 100 Ω
  4. 450 Ω

Explanation

The resistor must drop 9 − 2 = 7 V while passing 20 mA (0.02 A). Using R = V/I gives 7/0.02 = 350 Ω, the nearest practical value.

Question 42Electronic Components and Devices

In a full-wave bridge rectifier, how many diodes conduct during each half cycle of the input?

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

Explanation

In a bridge rectifier, one pair of opposite diodes conducts during the positive half cycle and the other pair during the negative half cycle. Thus exactly two diodes conduct at any instant.

Question 43Electronic Components and Devices

What is the main purpose of a filter capacitor connected across the output of a rectifier?

  1. To smooth the pulsating DC by charging and discharging Correct answer.
  2. To block DC from reaching the load
  3. To step up the output voltage
  4. To increase the AC ripple

Explanation

A filter capacitor charges near the peak of each rectified pulse and discharges into the load between pulses, reducing ripple and producing smoother DC. It does not increase voltage or block the DC output.

Question 44Electronic Components and Devices

A zener diode with a breakdown voltage of 5.1 V is used in a regulator. What is its normal operating condition?

  1. Unbiased with no applied voltage
  2. Forward biased well above 0.7 V
  3. Forward biased with zero current
  4. Reverse biased in the breakdown region Correct answer.

Explanation

A zener regulator operates with the diode reverse biased in its controlled breakdown region, where the voltage across it stays approximately constant at the zener voltage. It is not used in heavy forward conduction for regulation.

Question 45Electronic Components and Devices

A transistor is used as a switch to drive a relay. In which region should it be driven for the ON state?

  1. Active region
  2. Cut-off region
  3. Saturation region Correct answer.
  4. Breakdown region

Explanation

For switching, a transistor is driven between cut-off (OFF, no collector current) and saturation (ON, minimum collector-emitter voltage). The active region is used for amplification, and breakdown is avoided.

Question 46Electronic Components and Devices

Which statement correctly distinguishes a relay from a transistor?

  1. A relay stores charge, while a transistor stores magnetic energy
  2. A relay works only with DC, while a transistor works only with AC
  3. A relay uses an electromagnetic coil to operate mechanical contacts, while a transistor switches electronically Correct answer.
  4. A relay amplifies signals linearly, while a transistor cannot switch

Explanation

A relay is an electromechanical device in which a coil magnetically moves contacts, providing isolation between control and load circuits. A transistor is a solid-state device that switches or amplifies electronically without moving parts.

Question 47Electronic Components and Devices

A capacitor is marked 4700 µF, 25 V. What does the 25 V rating indicate?

  1. The voltage at which the capacitor fully charges in one second
  2. The AC ripple voltage it generates
  3. The maximum DC voltage the capacitor can safely withstand Correct answer.
  4. The minimum voltage needed for it to store charge

Explanation

The voltage rating of a capacitor is the maximum working voltage it can safely withstand without dielectric breakdown. Exceeding it risks failure, while any applied voltage below it will still charge the capacitor.

Question 48Electronic Components and Devices

In a common-emitter transistor circuit, a small base current controls a much larger collector current. Which quantity expresses this relationship?

  1. Power factor
  2. Current gain (hFE or β) Correct answer.
  3. Ripple factor
  4. Tolerance

Explanation

The DC current gain of a BJT, denoted hFE or β, is the ratio of collector current to base current. Power factor, tolerance, and ripple factor belong to AC circuits, components, and power supplies respectively.

Question 49Electronic Components and Devices

A student measures 0 Ω across a diode in both directions with a multimeter. What is the most likely conclusion?

  1. The diode is open-circuited
  2. The diode is working normally
  3. The diode is short-circuited Correct answer.
  4. The diode is a zener diode

Explanation

A good diode shows low resistance in forward bias and high resistance in reverse bias. A near-zero reading in both directions indicates the junction is shorted and the diode has failed.

Question 50Electronic Components and Devices

Which combination of gates is equivalent to a NAND gate?

  1. An OR gate followed by a NOT gate
  2. Two NOT gates in series
  3. An AND gate followed by a NOT gate Correct answer.
  4. An XOR gate followed by an AND gate

Explanation

A NAND gate produces the inverse of the AND function, so it is realised by an AND gate whose output passes through a NOT gate. An OR gate followed by NOT gives NOR instead.