Electronics and Modern Physics Competitive Exams
100 questions · General Science
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Question 1 of 100
Nuclear fission involves:
ExplanationNuclear fission is the splitting of a heavy nucleus (like Uranium-235) into two lighter nuclei, releasing energy.
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Question 2 of 100
Which device converts digital signals to analog signals?
ExplanationA DAC converts discrete digital values into a continuous analog signal.
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Question 3 of 100
Radioactive decay in which a nucleus emits a helium nucleus is called:
ExplanationAlpha decay involves emission of an alpha particle, which is essentially a helium-4 nucleus (2 protons + 2 neutrons).
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Question 4 of 100
How many bits make one byte?
ExplanationA byte conventionally consists of 8 bits.
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Question 5 of 100
An operational amplifier (op-amp) ideally has:
ExplanationAn ideal op-amp has infinite input impedance (draws no current) and zero output impedance (no voltage drop).
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Question 6 of 100
Which type of radioactive emission has the least penetrating power?
ExplanationAlpha particles, being heavy and highly charged, have the least penetrating power and can be stopped by a sheet of paper or skin.
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Question 7 of 100
A bridge rectifier (full-wave) typically uses how many diodes?
ExplanationA bridge rectifier uses four diodes arranged to allow full-wave rectification without needing a center-tapped transformer.
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Question 8 of 100
In the Bohr model, an electron emits energy when it:
ExplanationElectrons emit photons of energy equal to the difference between energy levels when transitioning from higher to lower orbits.
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Question 9 of 100
Who proposed the photoelectric effect explanation using photons?
ExplanationEinstein explained the photoelectric effect in 1905 by proposing light consists of discrete energy packets called photons, earning him the 1921 Nobel Prize.
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Question 10 of 100
X-rays were discovered by:
ExplanationWilhelm Röntgen discovered X-rays in 1895, earning the first Nobel Prize in Physics in 1901.
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Question 11 of 100
Who proposed that electrons orbit the nucleus in fixed energy levels?
ExplanationBohr proposed that electrons occupy discrete, quantized energy levels (orbits) around the nucleus.
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Question 12 of 100
The Compton effect demonstrates:
ExplanationThe Compton effect shows that X-ray photons scattering off electrons lose energy and change wavelength, confirming photons carry momentum like particles.
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Question 13 of 100
Which semiconductor doping creates 'holes' as majority carriers?
ExplanationP-type doping adds trivalent impurities, creating holes (electron deficiencies) as majority charge carriers.
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Question 14 of 100
If a radioactive substance has a half-life of 10 years, after 30 years what fraction remains?
ExplanationAfter 3 half-lives (30 years ÷ 10 years = 3), the remaining fraction is (1/2)³ = 1/8.
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Question 15 of 100
A half-wave rectifier uses how many diodes?
ExplanationA half-wave rectifier uses a single diode, conducting during only one half of the AC cycle.
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Question 16 of 100
Power in a DC circuit is calculated as:
ExplanationElectrical power P equals voltage V multiplied by current I (P = VI).
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Question 17 of 100
A transistor has how many terminals?
ExplanationA bipolar junction transistor has three terminals: emitter, base, and collector.
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Question 18 of 100
Heisenberg's Uncertainty Principle states that it is impossible to simultaneously know with perfect precision a particle's:
ExplanationHeisenberg's Uncertainty Principle states that the more precisely a particle's position is known, the less precisely its momentum can be known, and vice versa.
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Question 19 of 100
The Barkhausen criterion for sustained oscillations requires loop gain to be:
ExplanationBarkhausen's criterion: loop gain magnitude = 1 and total phase shift = 0° (or multiple of 360°) for sustained oscillation.
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Question 20 of 100
A thermistor is a sensor whose resistance changes with:
ExplanationA thermistor's resistance varies significantly with temperature changes, used in temperature sensing.
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Question 21 of 100
Which of the following is a passive electronic component?
ExplanationA resistor is passive (doesn't amplify or control signal flow); transistors, diodes, and ICs are active.
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Question 22 of 100
A positron is best described as:
ExplanationA positron is the antimatter counterpart of the electron: same mass, but positive charge instead of negative.
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Question 23 of 100
Which material is a good insulator?
ExplanationRubber does not conduct electricity well and is commonly used to insulate electrical wires.
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Question 24 of 100
Time dilation in Special Relativity means that time, as observed by a stationary observer, for a fast-moving clock:
ExplanationTime dilation predicts that a clock moving relative to an observer ticks slower than a stationary clock, as confirmed by experiments with fast particles and satellites.
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Question 25 of 100
The unit of electric current is:
ExplanationCurrent is measured in amperes (A).
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Question 26 of 100
The de Broglie hypothesis proposed that:
ExplanationLouis de Broglie proposed that all matter, not just light, has an associated wavelength (wave-particle duality).
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Question 27 of 100
A moderator in a nuclear reactor is used to:
ExplanationA moderator (like water or graphite) slows fast neutrons to increase the probability of sustaining fission chain reactions.
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Question 28 of 100
A rectifier is used to convert:
ExplanationA rectifier converts alternating current (AC) into direct current (DC).
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Question 29 of 100
Which logic gate produces an output of 1 if at least one input is 1?
ExplanationAn OR gate outputs HIGH if any one or more of its inputs is HIGH.
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Question 30 of 100
In a transistor, the thin and lightly doped middle region is called the:
ExplanationThe base is the thin, lightly doped middle region controlling current flow between emitter and collector.
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Question 31 of 100
Gamma rays are a form of:
ExplanationGamma rays are high-energy electromagnetic radiation, unlike alpha and beta particles which are particulate.
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Question 32 of 100
Population inversion, necessary for laser action, refers to:
ExplanationPopulation inversion means more atoms occupy a higher energy state than a lower one, a prerequisite for sustained stimulated emission (lasing).
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Question 33 of 100
LASER stands for:
ExplanationLASER is an acronym for Light Amplification by Stimulated Emission of Radiation.
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Question 34 of 100
Which material is commonly used as a conductor in electrical wiring?
ExplanationCopper is widely used in wiring due to its excellent electrical conductivity and reasonable cost.
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Question 35 of 100
In a Wheatstone bridge, the bridge is said to be 'balanced' when:
ExplanationA Wheatstone bridge is balanced when the ratio of resistances on both arms are equal, resulting in zero current through the galvanometer.
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Question 36 of 100
Which of the following is a semiconductor material?
ExplanationSilicon is a semiconductor; copper, aluminum and iron are conductors.
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Question 37 of 100
Which type of radioactive emission has the greatest penetrating power?
ExplanationGamma rays have the highest penetrating power among the three, able to pass through several centimeters of lead, unlike alpha (stopped by paper) or beta (stopped by thin metal).
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Question 38 of 100
Which component is used to smooth the output of a rectifier?
ExplanationA filter capacitor smooths pulsating DC output from a rectifier into a steadier DC voltage.
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Question 39 of 100
Stimulated emission occurs when a photon interacts with an atom in an excited state causing it to:
ExplanationStimulated emission causes an excited atom to emit a photon identical in phase, frequency, and direction to the incoming photon, dropping to a lower energy state.
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Question 40 of 100
A diode allows current to flow in:
ExplanationA diode is a one-way valve for current, conducting only when forward biased.
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Question 41 of 100
Ohm's Law states that V equals:
ExplanationOhm's Law: V = IR, where V is voltage, I is current, R is resistance.
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Question 42 of 100
NPN and PNP are types of:
ExplanationNPN and PNP describe the doping arrangement of bipolar junction transistors (BJTs).
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Question 43 of 100
NAND and NOR gates are called 'universal gates' because:
ExplanationNAND and NOR gates are universal because all basic gates (AND, OR, NOT) can be constructed from them alone.
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Question 44 of 100
James Chadwick is credited with the discovery of the:
ExplanationJames Chadwick discovered the neutron in 1932, confirming a neutral particle exists in the nucleus.
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Question 45 of 100
A NOT gate is also called a(n):
ExplanationA NOT gate inverts the input signal, hence it's also called an inverter.
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Question 46 of 100
Isotopes of an element have the same number of protons but different numbers of:
ExplanationIsotopes share the same atomic number (protons) but differ in neutron number, giving different mass numbers.
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Question 47 of 100
According to Special Relativity, as an object's speed approaches the speed of light, its mass (relativistic mass):
ExplanationSpecial Relativity shows that an object's relativistic mass increases as its speed approaches the speed of light, requiring more energy to accelerate further.
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Question 48 of 100
The energy released in nuclear reactions is explained by Einstein's equation:
ExplanationEinstein's mass-energy equivalence E = mc² explains how a small amount of mass converts into a large amount of energy in nuclear reactions.
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Question 49 of 100
A transformer works on the principle of:
ExplanationTransformers transfer energy between circuits via electromagnetic induction using a changing magnetic flux.
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Question 50 of 100
Nuclear fusion involves:
ExplanationNuclear fusion combines light nuclei (like hydrogen isotopes) into a heavier nucleus, releasing large amounts of energy, as occurs in the Sun.
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Question 51 of 100
A Schmitt trigger circuit is primarily used for:
ExplanationA Schmitt trigger uses hysteresis to convert noisy or slowly changing input signals into sharp, clean digital transitions.
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Question 52 of 100
Negative feedback in an amplifier circuit:
ExplanationNegative feedback trades off gain for improved stability, reduced distortion, and wider bandwidth.
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Question 53 of 100
Which component stores electrical energy in an electric field?
ExplanationA capacitor stores energy in an electric field between its plates.
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Question 54 of 100
Which particle has no electric charge and resides in the nucleus?
ExplanationThe neutron is electrically neutral and, along with protons, makes up the atomic nucleus.
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Question 55 of 100
The threshold frequency in the photoelectric effect is the minimum frequency needed to:
ExplanationBelow the threshold frequency, no photoelectrons are emitted regardless of light intensity, since each photon lacks sufficient energy.
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Question 56 of 100
Quantum tunneling refers to the phenomenon where a particle:
ExplanationQuantum tunneling describes how particles have a nonzero probability of passing through energy barriers higher than their own kinetic energy, due to their wave nature.
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Question 57 of 100
An oscillator circuit is used to generate:
ExplanationAn oscillator converts DC power into a continuous AC output waveform using positive feedback.
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Question 58 of 100
Who proposed the planetary model of the atom with a dense nucleus?
ExplanationRutherford's gold foil experiment led him to propose that atoms have a small, dense, positively charged nucleus.
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Question 59 of 100
The 'mass defect' of a nucleus refers to the:
ExplanationMass defect is the small amount of mass 'missing' when nucleons combine into a nucleus; this mass is converted to binding energy per E=mc².
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Question 60 of 100
Control rods in a nuclear reactor are used to:
ExplanationControl rods (often made of boron or cadmium) absorb neutrons to regulate and control the fission chain reaction rate.
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Question 61 of 100
A Zener diode is primarily used for:
ExplanationZener diodes are designed to operate in reverse breakdown to provide stable voltage regulation.
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Question 62 of 100
An electron volt (eV) is a unit of:
ExplanationAn electron volt is a unit of energy, defined as the energy gained by an electron moving through a potential difference of one volt.
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Question 63 of 100
A full-wave rectifier using two diodes requires a:
ExplanationA center-tapped full-wave rectifier uses two diodes with a center-tapped transformer secondary.
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Question 64 of 100
The photoelectric effect demonstrates that light behaves as:
ExplanationThe photoelectric effect shows light can behave as discrete particles (photons) that eject electrons from a metal surface.
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Question 65 of 100
A Geiger counter is used to detect:
ExplanationA Geiger counter detects ionizing radiation (alpha, beta, gamma) by measuring ionization in a gas-filled tube.
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Question 66 of 100
The half-life of a radioactive substance is the time taken for:
ExplanationHalf-life is the time required for half the radioactive atoms in a sample to undergo decay.
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Question 67 of 100
The mass number of an atom equals:
ExplanationMass number (A) is the total count of protons and neutrons (nucleons) in the nucleus.
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Question 68 of 100
The main advantage of a MOSFET over a BJT is:
ExplanationMOSFETs have extremely high input impedance since the gate is insulated, drawing almost no input current.
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Question 69 of 100
The atomic number of an element represents the number of:
ExplanationAtomic number (Z) equals the number of protons in an atom's nucleus, defining the element.
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Question 70 of 100
Which semiconductor doping creates excess electrons?
ExplanationN-type doping adds pentavalent impurities that contribute extra free electrons as majority carriers.
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Question 71 of 100
Radioactive decay in which a nucleus emits a high-energy electron is called:
ExplanationBeta decay involves a neutron converting to a proton and emitting a beta particle (electron) and antineutrino.
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Question 72 of 100
Which logic gate produces an output of 1 only when all inputs are 1?
ExplanationAn AND gate outputs HIGH (1) only if all its inputs are HIGH.
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Question 73 of 100
A MOSFET is primarily controlled by:
ExplanationA MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a voltage-controlled device, unlike BJTs which are current-controlled.
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Question 74 of 100
General Relativity describes gravity as a result of:
ExplanationGeneral Relativity reinterprets gravity not as a force but as the curvature of spacetime caused by the presence of mass and energy.
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Question 75 of 100
An LED converts electrical energy into:
ExplanationA Light Emitting Diode (LED) emits light when current passes through it in forward bias.
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Question 76 of 100
A microprocessor's clock speed is measured in:
ExplanationClock speed, indicating processing cycles per second, is measured in hertz (e.g., GHz).
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Question 77 of 100
The unit of electrical resistance is:
ExplanationResistance is measured in ohms (Ω).
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Question 78 of 100
Wave-particle duality refers to the concept that:
ExplanationWave-particle duality is a core concept of quantum mechanics: both light and matter show characteristics of both waves and particles depending on the experiment.
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Question 79 of 100
Einstein's theory of Special Relativity primarily deals with objects:
ExplanationSpecial Relativity addresses physics in inertial (non-accelerating) reference frames, especially effects at speeds approaching light speed.
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Question 80 of 100
The energy of a photon is given by:
ExplanationPhoton energy E equals Planck's constant h times frequency f (E = hf).
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Question 81 of 100
A flip-flop in digital electronics is used as a:
ExplanationA flip-flop is a bistable multivibrator circuit used as the fundamental building block of digital memory, storing one bit.
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Question 82 of 100
Planck's constant has units of:
ExplanationPlanck's constant (h ≈ 6.626 × 10⁻³⁴) has units of energy × time, i.e., joule-seconds.
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Question 83 of 100
In digital electronics, the smallest unit of data is called a:
ExplanationA bit (binary digit) is the smallest unit of digital data, representing either 0 or 1.
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Question 84 of 100
Marie Curie is known for her research on:
ExplanationMarie Curie pioneered research on radioactivity, discovering the elements polonium and radium, and won Nobel Prizes in both Physics and Chemistry.
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Question 85 of 100
A step-up transformer:
ExplanationA step-up transformer increases voltage while proportionally decreasing current, keeping power roughly constant.
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Question 86 of 100
Nuclear binding energy is defined as the energy required to:
ExplanationNuclear binding energy is the energy needed to disassemble a nucleus into its separate, unbound protons and neutrons; it is also the energy released upon formation.
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Question 87 of 100
Which component stores electrical energy in a magnetic field?
ExplanationAn inductor stores energy in a magnetic field created by current flow.
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Question 88 of 100
A photodiode is a sensor that detects:
ExplanationA photodiode generates current in response to incident light, used in light sensing applications.
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Question 89 of 100
An integrated circuit (IC) combines multiple components on a single:
ExplanationAn IC integrates transistors, diodes, resistors and capacitors onto a single small semiconductor chip.
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Question 90 of 100
A fuse in an electrical circuit is used to:
ExplanationA fuse melts and breaks the circuit when current exceeds a safe limit, protecting the circuit.
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Question 91 of 100
Which transistor configuration provides current gain but no voltage gain?
ExplanationThe common collector (emitter follower) configuration has high current gain but voltage gain close to 1.
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Question 92 of 100
Which of these is an example of an active component?
ExplanationTransistors are active components (can amplify/control signals); resistors, capacitors and inductors are passive.
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Question 93 of 100
Laser light is characterized by being:
ExplanationLaser light is coherent (waves in phase), monochromatic (single wavelength), and highly directional (low divergence).
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Question 94 of 100
Who developed the General Theory of Relativity?
ExplanationAlbert Einstein published the General Theory of Relativity in 1915, describing gravity as the curvature of spacetime.
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Question 95 of 100
J.J. Thomson is credited with the discovery of the:
ExplanationJ.J. Thomson discovered the electron in 1897 through his cathode ray tube experiments.
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Question 96 of 100
A nuclear reactor uses what process to generate energy?
ExplanationNuclear reactors harness controlled nuclear fission chain reactions to generate heat, which produces electricity.
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Question 97 of 100
What does 'PN junction' refer to in electronics?
ExplanationA PN junction is formed where p-type and n-type semiconductors meet, forming the basis of diodes.
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Question 98 of 100
X-rays are produced when high-speed electrons:
ExplanationX-rays are produced via bremsstrahlung (braking radiation) when fast electrons decelerate rapidly upon hitting a metal target.
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Question 99 of 100
Which device converts analog signals to digital signals?
ExplanationAn ADC samples and quantizes a continuous analog signal into discrete digital values.
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Question 100 of 100
The photoelectric equation (Einstein's) is given by:
ExplanationEinstein's photoelectric equation states the maximum kinetic energy of ejected electrons equals photon energy (hf) minus the work function (φ) of the metal.
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