Modern Physics MCQs 2026

Einstein's photoelectric equation is given by

1. A E = hf only ✓
2. B hf = work function + maximum kinetic energy of photoelectron ✓
3. C hf = mc squared ✓
4. D E = mc squared minus hf ✓

A Geiger-Muller counter is used to

1. A Produce X-rays ✓
2. B Accelerate particles ✓
3. C Detect and measure ionizing radiation ✓
4. D Generate a magnetic field ✓

The binding energy per nucleon curve shows that nuclei with the highest stability lie around

1. A Very light elements like hydrogen ✓
2. B Very heavy elements like uranium ✓
3. C Radioactive elements only ✓
4. D Mass number around iron (A approximately 56) ✓

Length contraction in special relativity states that an object in motion appears

1. A Longer along the direction of motion ✓
2. B Unchanged in all directions ✓
3. C Longer in all directions ✓
4. D Shorter along the direction of motion, as measured by a stationary observer ✓

Time dilation in special relativity predicts that a moving clock, as observed from a stationary frame, appears to

1. A Run faster ✓
2. B Stop completely ✓
3. C Run slower than a stationary clock ✓
4. D Show no change ✓

One of the postulates of Einstein's special theory of relativity is that

1. A The speed of light in vacuum is the same for all observers ✓
2. B Time is absolute for all observers ✓
3. C Mass never changes with velocity ✓
4. D Gravity affects light differently for each observer ✓

A transistor is mainly used in circuits as

1. A A source of light ✓
2. B A magnetic field generator ✓
3. C An amplifier or a switch ✓
4. D A capacitor ✓

Millikan's oil drop experiment was used to determine the

1. A Charge of an electron ✓
2. B Mass of a proton ✓
3. C Speed of light ✓
4. D Charge of a neutron ✓

Among alpha, beta, and gamma radiation, the one that can be stopped by just a sheet of paper is

1. A Gamma ✓
2. B Beta ✓
3. C Both beta and gamma ✓
4. D Alpha ✓

Carbon-14, used in radiocarbon dating, is an example of

1. A A radioactive isotope of carbon ✓
2. B A stable isotope only ✓
3. C An artificially created element ✓
4. D A noble gas ✓

In the photoelectric effect, increasing the intensity of incident light (above threshold frequency) increases the

1. A Kinetic energy of each photoelectron ✓
2. B Threshold frequency ✓
3. C Number of photoelectrons emitted per second ✓
4. D Work function of the metal ✓

The stopping potential in a photoelectric experiment is the voltage required to

1. A Increase electron emission ✓
2. B Just stop the most energetic photoelectrons from reaching the collector ✓
3. C Start photoemission ✓
4. D Double the current ✓

The energy levels of electrons in the Bohr model are

1. A Continuous ✓
2. B Random ✓
3. C Unlimited in number of transitions with no energy defined ✓
4. D Quantized, meaning electrons can only occupy specific discrete energy values ✓

Cathode rays, discovered by J.J. Thomson, are streams of

1. A Protons ✓
2. B Electrons ✓
3. C Neutrons ✓
4. D Photons ✓

PET (Positron Emission Tomography) scans rely on the detection of

1. A X-rays only ✓
2. B Gamma rays produced by positron-electron annihilation ✓
3. C Magnetic resonance signals ✓
4. D Ultraviolet radiation ✓

The word LASER is an acronym for

1. A Light Amplification by Sound Emission of Radiation ✓
2. B Light Absorption by Stimulated Emission of Radiation ✓
3. C Light Amplification by Stimulated Emission of Radiation ✓
4. D Long Amplitude Stimulated Emission of Rays ✓

Particle accelerators are used to

1. A Slow down particles for study ✓
2. B Cool particles to absolute zero ✓
3. C Store particles indefinitely ✓
4. D Accelerate charged particles to very high energies for collision experiments ✓

Quarks are considered

1. A Fundamental particles that combine to form protons and neutrons ✓
2. B Larger than protons ✓
3. C Made up of electrons ✓
4. D A type of photon ✓

The neutrino is a particle that

1. A Carries a strong positive charge ✓
2. B Is nearly massless, chargeless, and rarely interacts with matter ✓
3. C Is identical to the electron ✓
4. D Is emitted only during fusion, never fission ✓

A positron is best described as

1. A A neutral version of the proton ✓
2. B Identical to an electron in every way ✓
3. C The antiparticle of the electron, having the same mass but opposite charge ✓
4. D A heavier version of the neutron ✓

In a nuclear chain reaction, neutrons released from one fission event

1. A Are immediately absorbed with no further effect ✓
2. B Have no role in sustaining the reaction ✓
3. C Only produce gamma rays ✓
4. D Go on to cause further fission events, sustaining the reaction ✓

The minimum mass of fissile material needed to sustain a chain reaction is called the

1. A Threshold mass ✓
2. B Binding mass ✓
3. C Critical mass ✓
4. D Rest mass ✓

The radioactive decay law states that the rate of decay of a radioactive sample is

1. A Directly proportional to the number of undecayed nuclei present ✓
2. B Independent of the number of nuclei ✓
3. C Inversely proportional to time ✓
4. D Constant regardless of sample size ✓

The photoelectric effect refers to the emission of electrons from a metal surface when

1. A Heated ✓
2. B Placed in a magnetic field ✓
3. C Subjected to high voltage ✓
4. D Exposed to light of sufficient frequency ✓

According to Planck's quantum theory, energy is emitted or absorbed in discrete packets called

1. A Photons only ✓
2. B Quanta ✓
3. C Electrons ✓
4. D Waves ✓

The Compton effect demonstrates that

1. A Photons possess momentum and can scatter off electrons like particles ✓
2. B Light travels only as a wave ✓
3. C Electrons have no mass ✓
4. D X-rays cannot be scattered ✓

The minimum energy required to eject an electron from a metal surface is called its

1. A Ionization energy ✓
2. B Binding energy ✓
3. C Work function ✓
4. D Threshold energy only for gases ✓

The threshold frequency in the photoelectric effect is the

1. A Minimum frequency of light below which no photoemission occurs ✓
2. B Maximum frequency of light possible ✓
3. C Frequency at which electrons stop being emitted ✓
4. D Frequency of the emitted electron ✓

The de Broglie wavelength of a particle is given by

1. A Lambda = hf ✓
2. B Lambda = c/f ✓
3. C Lambda = mc squared ✓
4. D Lambda = h divided by p (Planck's constant divided by momentum) ✓

The concept that matter exhibits both particle and wave properties is called

1. A Quantum tunneling ✓
2. B Pair production ✓
3. C Wave-particle duality ✓
4. D Nuclear fission ✓

In Bohr's atomic model, electrons revolve around the nucleus in

1. A Random paths ✓
2. B Fixed, quantized orbits without radiating energy ✓
3. C Elliptical paths only ✓
4. D Straight lines ✓

The Balmer series in the hydrogen spectrum corresponds to electron transitions ending at

1. A n = 2 ✓
2. B n = 1 ✓
3. C n = 3 ✓
4. D n = infinity ✓

Rutherford's alpha scattering experiment led to the discovery of the

1. A Electron ✓
2. B Neutron ✓
3. C Atomic nucleus ✓
4. D Proton's charge ✓

X-rays are produced when

1. A Slow electrons strike a light target ✓
2. B Protons collide with neutrons ✓
3. C Alpha particles pass through gas ✓
4. D High-speed electrons are suddenly decelerated upon striking a metal target ✓

Alpha particles are essentially

1. A Helium nuclei (2 protons and 2 neutrons) ✓
2. B Fast-moving electrons ✓
3. C High-energy photons ✓
4. D Neutrons only ✓

Among alpha, beta, and gamma radiation, the one with the greatest penetrating power is

1. A Alpha ✓
2. B Gamma ✓
3. C Beta ✓
4. D All have equal penetrating power ✓

Beta particles emitted during radioactive decay are essentially

1. A Helium nuclei ✓
2. B High-speed electrons (or positrons) ✓
3. C Neutral photons ✓
4. D Protons ✓

Gamma rays emitted in radioactive decay are

1. A Charged particles ✓
2. B Helium nuclei ✓
3. C Electrons ✓
4. D High-energy electromagnetic radiation with no charge or mass ✓

The time taken for half of the radioactive nuclei in a sample to decay is called

1. A Decay constant ✓
2. B Mean life ✓
3. C Half-life ✓
4. D Activity period ✓

Nuclear fission involves

1. A Splitting of a heavy nucleus into lighter nuclei with release of energy ✓
2. B Combining light nuclei into a heavier nucleus ✓
3. C Emission of a single alpha particle ✓
4. D Absorption of energy by the nucleus ✓

In a semiconductor diode, current flows easily when it is

1. A Reverse biased ✓
2. B Forward biased ✓
3. C Not connected to a circuit ✓
4. D Cooled to absolute zero ✓

Nuclear fusion involves

1. A Splitting heavy nuclei ✓
2. B Combining light nuclei into a heavier nucleus with release of energy ✓
3. C Absorbing electrons ✓
4. D Emitting gamma rays only ✓

The mass defect in a nucleus refers to the

1. A Extra mass gained during fusion ✓
2. B Mass of the electron cloud ✓
3. C Difference between the sum of masses of nucleons and the actual nuclear mass ✓
4. D Mass of the proton alone ✓

According to Einstein's mass-energy relation, energy E released from mass defect delta-m is given by

1. A E = delta-m times c squared ✓
2. B E = delta-m times c ✓
3. C E = delta-m divided by c squared ✓
4. D E = delta-m times g ✓

The atomic number of an element represents the number of

1. A Neutrons in the nucleus ✓
2. B Total nucleons ✓
3. C Electrons in the outer shell only ✓
4. D Protons in the nucleus ✓

A laser produces light that is

1. A Incoherent and divergent ✓
2. B Made up of many different wavelengths ✓
3. C Similar to ordinary bulb light ✓
4. D Coherent, monochromatic, and highly directional ✓

Isotopes of an element have the same number of protons but different numbers of

1. A Electrons ✓
2. B Neutrons ✓
3. C Protons ✓
4. D Valence shells ✓

A nuclear reactor uses a moderator to

1. A Increase neutron speed ✓
2. B Absorb all neutrons ✓
3. C Convert neutrons to protons ✓
4. D Slow down fast neutrons to sustain a controlled chain reaction ✓

The three fundamental particles that make up an atom are

1. A Protons, neutrons, and electrons ✓
2. B Quarks, leptons, and bosons only ✓
3. C Protons, neutrons, and quarks ✓
4. D Electrons, neutrinos, and photons ✓

Heisenberg's uncertainty principle states that it is impossible to simultaneously determine with perfect accuracy a particle's

1. A Charge and mass ✓
2. B Energy and charge ✓
3. C Exact position and momentum ✓
4. D Spin and charge ✓