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Modern Physics Questions

Practice 139 Modern Physics questions with detailed answers and explanations. Free MCQs, PYQs, and mock test questions for NEET, JEE, GATE, SSC and more.

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Practice by Exam:Physics(138)Chemistry(1)

About Modern Physics — practice questions, PYQs & concepts

Modern Physics is a frequently-tested topic on Physics, Chemistry. ExamTest.live currently lists 139 Modern Physics questions spanning previous-year papers from 2026 to 2026, each with worked solutions and a step-by-step explanation. Use the filters on this page to focus on a specific exam, difficulty level or year — every answer key is free, no sign-up required.

Modern Physics weight in competitive exams

Across our Modern Physics question bank, the largest sources are Physics (138) and Chemistry (1). Click any exam chip above to drill down to that exam-specific question set.

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  • Start easy: 30 easy Modern Physics questions are available — build fluency before moving up.
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All Modern Physics Questions(1–100 of 139)

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Q1hardmcqPhysicsAIEEE 20042026
50% accuracy
A nucleus disintegrates into two nuclear parts which have their velocities in the ratio . The ratio of their nuclear sizes will be:
Q2hardmcqPhysicsAIEEE 20042026
50% accuracy
An -particle of energy is scattered through by a fixed uranium nucleus (). The distance of the closest approach is of the order of:
Q3mediummcqPhysicsAIEEE 20042026
0% accuracy
The binding energy per nucleon of deuteron () and helium nucleus () is and respectively. If two deuteron nuclei react to form a single helium nucleus, then the energy released is:
Q4easymcqPhysicsAIEEE 20042026
50% accuracy
According to Einstein’s photoelectric equation, the plot of the kinetic energy of the emitted photo electrons from a metal vs the frequency of the incident radiation gives a straight line whose slope:
Q5mediummcqPhysicsAIEEE 20042026
50% accuracy
The work function of a substance is . Then the longest wavelength of light that can cause photoelectron emission from this substance is approximately:
Q6mediummcqPhysicsAIEEE 20062026
0% accuracy
The threshold frequency for a metallic surface corresponds to an energy of , and the stopping potential for a radiation incident on this surface is . The incident radiation lies in the:
Q7mediummcqPhysicsNEET 20192026
0% accuracy
An electron is accelerated through a potential difference of . Its de Broglie wavelength is, (nearly): ()
Q8mediummcqPhysicsAIEEE 20062026
0% accuracy
The anode voltage of a photocell is kept fixed. The wavelength of the light falling on the cathode is gradually changed. The plate current of the photocell varies as follows:
image
Q9easymcqPhysicsNEET 20192026
0% accuracy
-particle consists of:
Q10easymcqPhysicsAIEEE 20062026
0% accuracy
The time taken by a photoelectron to come out after the photon strikes is approximately:
Q11mediummcqPhysicsAIEEE 20072026
0% accuracy
A photon of frequency has a momentum associated with it. If is the velocity of light, the momentum is:
Q12easymcqPhysicsNEET 20192026
0% accuracy
The total energy of an electron in an atom in an orbit is . Its kinetic and potential energies are, respectively:
Q13mediummcqPhysicsAIEEE2026
Statement-1: When ultraviolet light is incident on a photocell, its stopping potential is and the maximum kinetic energy of the photoelectrons is . When the ultraviolet light is replaced by X-rays, both and increase.Statement-2: Photoelectrons are emitted with speeds ranging from zero to a maximum value because of the range of frequencies present in the incident light.
Q14mediummcqPhysicsNEET 20232026
The minimum wavelength of X-rays produced by an electron accelerated through a potential difference of volts is proportional to:
Q15mediummcqPhysicsNEET 20232026
The half-life of a radioactive substance is . In how much time, the activity of the substance drops to of its initial value?
Q16mediummcqPhysicsJEE Main2026
In a hydrogen like atom electron makes transition from an energy level with quantum number to another with quantum number . If , the frequency of radiation emitted is proportional to:
Q17mediummcqPhysicsNEET 20222026
The graph which shows the variation of the de Broglie wavelength () of a particle and its associated momentum () is:
image
Q18easymcqChemistryNEET 20212026
Tritium, a radioactive isotope of hydrogen, emits which of the following particles?
Q19easymcqPhysicsAIEEE 20122026
Statement 1: Davisson-Germer experiment established the wave nature of electrons.Statement 2: If electrons have wave nature, they can interfere and show diffraction.
Q20mediummcqPhysicsNEET 20172026
The ratio of wavelengths of the last line of Balmer series and the last line of Lyman series is:
Q21easymcqPhysicsNEET (UG) 20242026
If is the velocity of light in free space, the correct statements about photon among the following are:A. The energy of a photon is .B. The velocity of a photon is .C. The momentum of a photon, .D. In a photon-electron collision, both total energy and total momentum are conserved.E. Photon possesses positive charge.Choose the correct answer:
Q22mediummcqPhysicsAIEEE2026
In an experiment, electrons pass through a narrow slit of width ‘ ’. They are detected on a screen at a distance ‘ ’. Which graph correctly represents the number of electrons detected as a function of the detector position ( corresponds to the middle of the slit)?
image
image
Q23mediummcqPhysicsAIEEE2026
If a source of power produces photons/second, the radiation belongs to a part of the spectrum called:
Q24mediummcqPhysicsAIEEE2026
A photocell is illuminated by a small bright source placed away. When the same source of light is placed away, the number of electrons emitted by photo cathode would:
Q25easymcqPhysicsNEET 20232026
The work functions of Caesium (Cs), Potassium (K) and Sodium (Na) are , and respectively. If incident electromagnetic radiation has an incident energy of , which of these photosensitive surfaces may emit photoelectrons?
Q26mediummcqPhysicsFIITJEE AIEEE 2011 (Set Q)2026
Statement-1 : A metallic surface is irradiated by a monochromatic light of frequency (the threshold frequency). The maximum kinetic energy and the stopping potential are and respectively. If the frequency incident on the surface is doubled, both the and are also doubled.Statement-2 : The maximum kinetic energy and the stopping potential of photoelectrons emitted from a surface are linearly dependent on the frequency of incident light.
Q27mediumassertion/reasoningPhysicsNEET (UG) 20242026
Given
Q28easymcqPhysicsNEET 20172026
The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature (Kelvin) and mass , is:
Q29hardmcqPhysicsNEET 20222026
When two monochromatic light of frequency and are incident on a photoelectric metal, their stopping potential becomes and respectively. The threshold frequency for this metal is:
Q30mediummcqPhysicsNEET 20212026
The number of photons per second on an average emitted by the source of monochromatic light of wavelength , when it delivers the power of will be ():
Q31mediummcqPhysicsNEET (UG) 20242026
In the nuclear emission sequence:
image
The mass number and atomic number of the product respectively, are:
Q32mediummcqPhysicsAIEEE2026
image
Electrons accelerated by potential are diffracted from a crystal. If and , should be about ():
Q33mediummcqPhysicsNEET (UG) 20242026
The graph which shows the variation of and its kinetic energy, is (where is de Broglie wavelength of a free particle):
image
Q34easymcqPhysicsAIEEE 20122026
Hydrogen atom is excited from ground state to another state with principal quantum number equal to 4. Then the number of spectral lines in the emission spectra will be:
Q35mediummcqPhysicsAIEEE2026
Starting with a sample of pure , of it decays into in . The corresponding half-life is:
Q36mediummcqPhysicsJEE Main2026
The anode voltage of a photocell is kept fixed. The wavelength of the light falling on the cathode is gradually changed. The plate current of the photocell varies as follows:
image
Q37hardmcqPhysicsNEET 20172026
The photoelectric threshold wavelength of silver is . The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength is [Given and ]:
Q38easymcqPhysicsAIEEE 20032026
The wavelengths involved in the spectrum of deuterium () are slightly different from that of hydrogen spectrum, because:
Q39mediummcqPhysicsFIITJEE AIEEE 2011 (Set Q)2026
The half life of a radioactive substance is . The approximate time interval between the time when of it has decayed and time when of it had decayed is:
Q40mediummcqPhysicsAIEEE2026
Statement - 1: Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion.Statement - 2: For heavy nuclei, binding energy per nucleon increases with increasing while for light nuclei it decreases with increasing .
Q41mediummcqPhysicsAIEEE 20092026
The surface of a metal is illuminated with the light of . The kinetic energy of the ejected photoelectrons was found to be . The work function of the metal is ():
Q42hardmcqPhysicsAIEEE 20032026
A nucleus with emits the following in a sequence: . The of the resulting nucleus is:
Q43hardmcqPhysicsAIEEE 20032026
If the binding energy of the electron in a hydrogen atom is , the energy required to remove the electron from the first excited state of is:
Q44mediummcqPhysicsNEET (UG) 20242026
Match List I with List II for transitions in Hydrogen spectrum (Balmer series):
image
Q45mediummcqPhysicsAIEEE2026
If a strong diffraction peak is observed when electrons are incident at an angle ‘ ’ from the normal to the crystal planes with distance ‘ ’ between them, de Broglie wavelength of electrons can be calculated by the relationship ( is an integer):
Q46easymcqPhysicsAIEEE 20032026
Which of the following cannot be emitted by radioactive substance during their decay?
Q47easymcqPhysicsAIEEE 20032026
Which of the following radiations has the least wavelength?
Q48mediummcqPhysicsAIEEE 20032026
A radioactive sample at any instant has its disintegration rate . After , the rate is . Then, the decay constant (per minute) is:
Q49mediummcqPhysicsAIEEE2026
A nuclear transformation is denoted by . Which of the following is the nucleus of element ?
Q50easymcqPhysicsAIEEE2026
The diagram shows the energy levels for an electron in a certain atom. Which transition shown represents the emission of a photon with the most energy?
image
Q51mediummcqPhysicsAIEEE 20032026
Which of the following atoms has the lowest ionization potential?
Q52mediummcqPhysicsAIEEE 20032026
When nucleus originally at rest, decays by emitting an alpha particle having a speed , the recoil speed of the residual nucleus is:
Q53easymcqPhysicsAIEEE2026
If the kinetic energy of a free electron doubles. Its de Broglie wavelength changes by the factor:
Q54hardmcqPhysicsAIEEE 20032026
In the nuclear fusion reaction , given that the repulsive potential energy between the two nuclei is , the temperature at which the gases must be heated to initiate the reaction is nearly: (Boltzmann’s constant )
Q55mediummcqPhysicsAIEEE2026
The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than is incident on it. The band gap in () for the semiconductor is:
Q56hardmcqPhysicsAIEEE2026
Suppose an electron is attracted towards the origin by a force where is a constant. By applying Bohr model, the radius and kinetic energy of the orbital are:
Q57mediummcqPhysicsAIEEE 20032026
Two identical photo cathodes receive light of frequencies and . If the velocities of the photoelectrons (of mass ) coming out are respectively and , then:
Q58mediummcqPhysicsAIEEE2026
If radius of nucleus is estimated to be then the radius nucleus be nearly:
Q59hardmcqPhysicsPhysics
0% accuracy
A photon and an electron (mass ) have the same energy . The ratio of their de-Broglie wavelengths is ( is the speed of light):
Q60hardmcqPhysicsPhysics
0% accuracy
A particle of mass is moving around the origin with a constant force pulling it towards the origin. If Bohr model is used to describe its motion, the radius of the orbit and the particle's speed in the orbit depend on as:
Q61easymcqPhysicsPhysics
0% accuracy
Which of the following options represents the variation of photoelectric current with intensity and frequency of light shown on the x-axis?

image
Q62mediummcqPhysicsPhysics
3% accuracy
The ratio of the wavelengths of the light absorbed by a Hydrogen atom when it undergoes and transitions, respectively, is:
Q63mediummcqPhysicsPhysics
3% accuracy
De-Broglie wavelength of an electron orbiting in the state of hydrogen atom is close to (Given Bohr radius ):
Q64hardmcqPhysicsPhysics
3% accuracy
A model for quantized motion of an electron in a uniform magnetic field states that the flux passing through the orbit of the electron is where is an integer, is Planck's constant and is the magnitude of electron's charge. According to the model, the magnetic moment of an electron in its lowest energy state will be ( is the mass of the electron):
Q65hardmcqPhysicsPhysics
3% accuracy
Energy and radius of first Bohr orbit of and are:[Given ]
Q66mediummcqPhysicsPhysics
0% accuracy
A radioactive nucleus of mass emits a photon of frequency and the nucleus recoils. The recoil energy will be:
Q67mediummcqPhysicsPhysics
0% accuracy
The power obtained in a reactor using disintegration is . The mass decay of per hour is:
Q68mediummcqPhysicsPhysics
0% accuracy
The wavelength of the first line of Lyman series for hydrogen atom is equal to that of the second line of Balmer series for a hydrogen-like ion. The atomic number of the hydrogen-like ion is:
Q69mediummcqPhysicsPhysics
0% accuracy
In photoelectric emission process from a metal of work function , the kinetic energy of most energetic electrons is . The corresponding stopping potential is:
Q70mediummcqPhysicsPhysics
0% accuracy
Electrons used in an electron microscope are accelerated by a voltage of . If the voltage is increased to , then the de-Broglie wavelength associated with the electrons would:
Q71mediummcqPhysicsPhysics
0% accuracy
Light of two different frequencies whose photons have energies and respectively illuminate a metallic surface whose work function is successively. The ratio of maximum speeds of emitted electrons will be:
Q72mediummcqPhysicsPhysics
0% accuracy
In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by:
Q73mediummcqPhysicsPhysics
0% accuracy
The half-life of a radioactive isotope is . It decays to another element which is stable. The two elements and were found to be in the ratio of in a sample of a given rock. The age of the rock was estimated to be:
Q74mediummcqPhysicsPhysics
0% accuracy
Photoelectric emission occurs only when the incident light has more than a certain minimum:
Q75mediummcqPhysicsPhysics
0% accuracy
Fusion reaction takes place at high temperature because:
Q76mediummcqPhysicsPhysics
0% accuracy
A nucleus emits one particle and two -particles. The resulting nucleus is:
Q77mediummcqPhysicsPhysics
When the energy of the incident radiation is increased by , the kinetic energy of the photoelectrons emitted from a metal surface increased from to . The work function of the metal is:
Q78mediummcqPhysicsPhysics
To get an output from the circuit shown below, the input must be ():
image
Q79easymcqPhysicsPhysics
If the kinetic energy of the particle is increased to times its previous value, the percentage change in the de-Broglie wavelength of the particle is:
Q80easymcqPhysicsPhysics
Hydrogen atom in ground state is excited by a monochromatic radiation of . Number of spectral lines in the resulting spectrum emitted will be:
Q81mediummcqPhysicsPhysics
A p-n photodiode is fabricated from a semiconductor with a band gap of . It can detect a signal of wavelength:
Q82mediummcqPhysicsPhysics
Threshold frequency for a metal is . If light of frequency is incident, the cut-off voltage is nearly:
Q83mediummcqPhysicsPhysics
The Binding energy per nucleon of and nuclei are and , respectively. In the nuclear reaction , the value of energy released is:
Q84mediummcqPhysicsPhysics
A radio isotope 'X' with a half life decays to 'Y' which is stable. A sample of the rock from a cave was found to contain 'X' and 'Y' in the ratio . The age of the rock is:
Q85mediummcqPhysicsPhysics
An electron in -atom jumps from to ground state. Work function of material is and stopping potential is . The value of is:
Q86hardmcqPhysicsPhysics
In the spectrum of hydrogen, the ratio of the longest wavelength in the Lyman series to the longest wavelength in the Balmer series is:
Q87easymcqPhysicsPhysics
In the given figure, a diode is connected to an external resistance and an e.m.f. of . If the barrier potential developed across the diode is , the current in the circuit will be:
image
Q88hardmcqPhysicsPhysics
A source emits monochromatic light of wavelength . When placed away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of , the number of photoelectrons liberated, will be reduced by a factor of:
Q89mediummcqPhysicsPhysics
The Figure shows a plot of photo current versus anode potential for a photo sensitive surface for three different radiations. Which one of the following is a correct statement?
image
Q90mediummcqPhysicsPhysics
Which is not a possible energy for a photon emitted by -atom?
Q91easymcqPhysicsPhysics
A nucleus of uranium decays at rest into nuclei of thorium and helium. Then:
Q92hardmcqPhysicsPhysics
Light of wavelength is incident on a metal with work function . The de Broglie wavelength of the emitted electron is:
Q93mediummcqPhysicsPhysics
Two nuclei () and () decay to . When , the number of nuclei present is:
Q94hardmcqPhysicsPhysics
A photoelectric surface is illuminated successively by monochromatic light of wavelength and . If the maximum kinetic energy of the emitted photoelectrons in the second case is times that in the first case, the work function of the surface of the material is:
Q95easymcqPhysicsPhysics
In a Rutherford scattering experiment when a projectile of charge and mass approaches a target nucleus of charge and mass , the distance of closest approach is . The energy of the projectile is:
Q96hardmcqPhysicsPhysics
When a metallic surface is illuminated with radiation of wavelength , the stopping potential is . If the same surface is illuminated with radiation of wavelength , the stopping potential is . The threshold wavelength for the metallic surface is:
Q97mediummcqPhysicsPhysics
Given the value of Rydberg constant is , the wave number of the last line of the Balmer series in hydrogen spectrum will be:
Q98hardmcqPhysicsPhysics
An electron of mass and a photon have same energy . The ratio of de-Broglie wavelengths associated with them is:
Q99easymcqPhysicsPhysics
When an -particle of mass moving with velocity bombards on a heavy nucleus of charge , its distance of closest approach from the nucleus depends on as:
Q100easymcqPhysicsPhysics
The total energy of electron in the ground state of hydrogen atom is . The kinetic energy of an electron in the first excited state is:
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