Modern Physics Practice Questions
19 free Modern Physics practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which scientist proposed the theory of relativity?
- A Albert Einstein
- B Isaac Newton
- C Niels Bohr
- D James Clerk Maxwell
Correct answer: Albert Einstein
Albert Einstein proposed the theory of relativity, which revolutionized physics by explaining the relationship between space, time, and energy. His work includes both special relativity (1905) and general relativity (1915).
Which phenomenon demonstrates the particle nature of light?
- A Reflection of light
- B Interference of light
- C Diffraction at a narrow slit
- D Photoelectric effect
Correct answer: Photoelectric effect
The photoelectric effect occurs when light strikes a metal surface and ejects electrons. This phenomenon shows that light behaves as particles called photons carrying discrete packets of energy.
According to quantum theory, energy is emitted or absorbed in discrete packets called:
- A Quanta
- B Ions
- C Electrons
- D Neutrons
Correct answer: Quanta
Quantum theory states that energy is emitted or absorbed in discrete amounts known as quanta. This concept was introduced by Max Planck to explain blackbody radiation.
What is the speed of light in a vacuum?
- A 3 × 10^6 m/s
- B 3 × 10^7 m/s
- C 3 × 10^9 m/s
- D 3 × 10^8 m/s
Correct answer: 3 × 10^8 m/s
The speed of light in a vacuum is approximately 3 × 10^8 meters per second. This constant is fundamental in modern physics and appears in Einstein's famous equation E = mc².
Which model describes electrons orbiting the nucleus in specific energy levels?
- A Bohr atomic model
- B Thomson model
- C Rutherford model
- D Quantum field model
Correct answer: Bohr atomic model
The Bohr model proposed that electrons move in fixed circular orbits around the nucleus with quantized energy levels. Electrons can jump between levels by absorbing or emitting energy.
What type of wave is associated with moving particles according to de Broglie?
- A Mechanical wave
- B Matter wave
- C Sound wave
- D Gravity wave
Correct answer: Matter wave
Louis de Broglie proposed that particles such as electrons exhibit wave-like behavior. These waves are called matter waves and are described by the de Broglie wavelength.
Which principle states that the position and momentum of a particle cannot both be precisely determined at the same time?
- A Pauli exclusion principle
- B Uncertainty principle
- C Relativity principle
- D Quantum tunneling principle
Correct answer: Uncertainty principle
Werner Heisenberg's uncertainty principle states that the position and momentum of a particle cannot both be measured with perfect precision simultaneously. This reflects the fundamental probabilistic nature of quantum mechanics.
Which particle carries a negative electric charge in an atom?
- A Proton
- B Neutron
- C Electron
- D Positron
Correct answer: Electron
Electrons are negatively charged subatomic particles that orbit the nucleus. They play a key role in electricity, chemical bonding, and many modern physics phenomena.
What does the equation E = mc² represent?
- A Energy conservation
- B Mass-energy equivalence
- C Quantum wave-particle duality
- D Gravitational force
Correct answer: Mass-energy equivalence
Einstein's equation E = mc² shows that mass and energy are interchangeable. A small amount of mass can be converted into a large amount of energy.
Which experiment provided the first direct experimental confirmation of de Broglie's hypothesis that electrons behave as waves?
- A Franck-Hertz experiment
- B Davisson-Germer experiment
- C Millikan oil drop experiment
- D Young's double-slit experiment
Correct answer: Davisson-Germer experiment
The Davisson-Germer experiment (1927) observed electrons diffracting from a nickel crystal lattice, with maxima matching the de Broglie wavelength. This was the first direct experimental evidence for matter waves.
Which particle is the antimatter counterpart of the electron?
- A Proton
- B Positron
- C Neutron
- D Antiproton
Correct answer: Positron
The positron is the antimatter counterpart of the electron. It has the same mass as an electron but carries a positive charge.
Which constant is fundamental in quantum mechanics and relates energy to frequency?
- A Boltzmann constant
- B Planck constant
- C Gravitational constant
- D Gas constant
Correct answer: Planck constant
The Planck constant (h) relates the energy of a photon to its frequency through the equation E = hf. It is a fundamental constant in quantum physics.
Which fundamental interaction is responsible for radioactive beta decay?
- A Strong force
- B Electromagnetic force
- C Gravitational force
- D Weak nuclear force
Correct answer: Weak nuclear force
Beta decay occurs through the weak nuclear force. This force allows a neutron to transform into a proton or vice versa while emitting particles.
Which scientist developed the quantum theory of blackbody radiation?
- A Max Planck
- B Albert Einstein
- C Erwin Schrödinger
- D Niels Bohr
Correct answer: Max Planck
Max Planck introduced the idea that energy is quantized while studying blackbody radiation. His work laid the foundation for the development of quantum mechanics.
What type of radiation consists of packets of electromagnetic energy called photons?
- A Alpha radiation
- B Beta radiation
- C Gamma radiation
- D Neutron radiation
Correct answer: Gamma radiation
Gamma radiation is a form of high-energy electromagnetic radiation. It consists of photons and has very high frequency and penetrating power.
Which modern physics concept explains why electrons do not collapse into the nucleus?
- A Quantum energy levels
- B Gravitational attraction
- C Magnetic force
- D Elastic collision
Correct answer: Quantum energy levels
Quantum mechanics states that electrons occupy discrete energy levels around the nucleus. These quantized states prevent electrons from spiraling into the nucleus.
Which mathematical equation describes the wave behavior of particles in quantum mechanics?
- A Newton's equation of motion
- B Maxwell's equations
- C Einstein field equation
- D Schrödinger equation
Correct answer: Schrödinger equation
The Schrödinger equation describes how the quantum state of a system evolves over time. It is a fundamental equation used to determine the probability distribution of particles.
What is the main idea behind wave-particle duality?
- A Particles behave only as waves and never as solid objects
- B Particles behave only as solid objects, never as waves
- C Particles exhibit both wave and particle properties
- D Particles have no physical form
Correct answer: Particles exhibit both wave and particle properties
Wave-particle duality states that particles such as electrons and photons can exhibit both wave-like and particle-like behavior depending on the experiment performed.
Which device uses the principles of quantum mechanics to produce coherent light?
- A Laser
- B Transistor
- C Capacitor
- D LED
Correct answer: Laser
A laser (Light Amplification by Stimulated Emission of Radiation) works using quantum principles. It produces highly coherent, monochromatic light through stimulated emission.