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Dual Nature of Radiation and Matter — MH-CET Physics MCQs with Solutions
Free MH-CET Physics Dual Nature of Radiation and Matter MCQs with step-by-step solutions covering Photoelectric Effect — Observations, Einstein's Photoelectric Equation, Work Function & Threshold, Photons & Photon Energy, de Broglie Waves, Davisson-Germer & Electron Microscope. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Photoelectric Effect — Observations · easy · theory
Photoelectric emission from a metal surface is:
A. Delayed by several minutes at low intensity
B. Observed only after prolonged illumination
C. Delayed by several seconds at low intensity
D. Practically instantaneous, with no measurable time lag ✓ Correct
Solution: Emission begins within about $10^{-9}\text{ s}$, which the wave theory could never explain for feeble light.
Q2 — Photoelectric Effect — Observations · easy · theory
If the frequency of the incident light is below the threshold frequency, photoemission:
A. Occurs only for metals of high work function
B. Does not occur however intense the light is ✓ Correct
C. Occurs if the light is made intense enough
D. Occurs after a long time delay
Solution: A single photon must carry enough energy on its own; piling up more photons does not help.
Q3 — Photoelectric Effect — Observations · easy · theory
For light of frequency above threshold, the photoelectric current is:
A. Proportional to the square of the intensity
B. Directly proportional to the intensity of the incident light ✓ Correct
C. Independent of the intensity
D. Inversely proportional to the intensity
Solution: Greater intensity means more photons per second and therefore more ejected electrons per second.
Q4 — Photoelectric Effect — Observations · easy · numerical
The intensity of light falling on a photocell is doubled, the frequency being unchanged. The photoelectric current:
A. Halves
B. Doubles ✓ Correct
C. Becomes four times
D. Remains unchanged
Solution: Twice as many photons arrive each second, so twice as many electrons are ejected.
Q5 — Photoelectric Effect — Observations · easy · numerical
The stopping potential is $1.5\text{ V}$. The maximum kinetic energy of the photoelectrons, in electron volt, is:
A. $1.5\text{ eV}$ ✓ Correct
B. $3.0\text{ eV}$
C. $0.75\text{ eV}$
D. $1.6\text{ eV}$
Solution: In electron volt the maximum kinetic energy is numerically equal to the stopping potential in volt.
Q6 — Photoelectric Effect — Observations · easy · numerical
The saturation current in a photocell is $4\text{ mA}$ for a certain intensity. If the intensity is doubled, the saturation current becomes:
A. $16\text{ mA}$
B. $2\text{ mA}$
C. $8\text{ mA}$ ✓ Correct
D. $4\text{ mA}$
Solution: Saturation current is proportional to intensity.
Q7 — Photoelectric Effect — Observations · easy · numerical
Two beams of the same frequency have intensities in the ratio $1 : 3$. The ratio of the saturation currents they produce is:
A. $1 : 3$ ✓ Correct
B. $1 : 1$
C. $1 : 9$
D. $3 : 1$
Solution: Saturation current is directly proportional to intensity.
Q8 — Photoelectric Effect — Observations · easy · numerical
In a photoelectric experiment the frequency of light is increased while the intensity is kept constant. The maximum kinetic energy of the photoelectrons:
A. Remains unchanged
B. Increases ✓ Correct
C. Decreases
D. Becomes zero
Solution: $K_{max} = h\nu - \phi_0$ grows linearly with frequency.
Q9 — Einstein's Photoelectric Equation · easy · theory
Einstein's photoelectric equation is:
A. $h\nu = \dfrac{\phi_0}{K_{max}}$
B. $h\nu = \phi_0 + K_{max}$ ✓ Correct
C. $h\nu = \phi_0 K_{max}$
D. $h\nu = \phi_0 - K_{max}$
Solution: The photon energy is shared between freeing the electron and giving it kinetic energy.
Q10 — Einstein's Photoelectric Equation · easy · theory
The maximum kinetic energy of a photoelectron in terms of the threshold frequency is:
A. $h\nu\nu_0$
B. $h(\nu + \nu_0)$
C. $\dfrac{h\nu}{\nu_0}$
D. $h(\nu - \nu_0)$ ✓ Correct
Solution: Since $\phi_0 = h\nu_0$, the excess photon energy above the work function appears as kinetic energy.
Q11 — Einstein's Photoelectric Equation · easy · theory
The existence of a threshold frequency is explained by the fact that:
A. The metal reflects low-frequency light
B. A photon must carry at least the work function energy to free an electron ✓ Correct
C. Light of low frequency is absorbed by the air
D. Electrons move too slowly at low frequency
Solution: Below $\nu_0$ the single-photon energy $h\nu$ is simply less than $\phi_0$.
Q12 — Einstein's Photoelectric Equation · easy · theory
Einstein received the Nobel Prize in Physics in 1921 principally for his explanation of the:
A. Structure of the atom
B. Photoelectric effect ✓ Correct
C. Theory of relativity
D. Brownian motion
Solution: The photoelectric work established the quantum nature of light beyond doubt.
Q13 — Einstein's Photoelectric Equation · easy · theory
The photoelectric effect provides direct evidence for the:
A. Particle nature of electromagnetic radiation ✓ Correct
B. Wave nature of electrons
C. Wave nature of electromagnetic radiation
D. Existence of the nucleus
Solution: Interference and diffraction show the wave side; the photoelectric effect shows the particle side.
Q14 — Einstein's Photoelectric Equation · easy · numerical
A photon of energy $5\text{ eV}$ falls on a metal of work function $2\text{ eV}$. The maximum kinetic energy of the photoelectron is:
A. $2.5\text{ eV}$
B. $7\text{ eV}$
C. $3\text{ eV}$ ✓ Correct
D. $2\text{ eV}$
Solution: $K_{max} = h\nu - \phi_0 = 5 - 2 = 3\text{ eV}$.
Q15 — Einstein's Photoelectric Equation · easy · numerical
At the threshold frequency, the maximum kinetic energy of the emitted photoelectrons is:
A. Maximum
B. Equal to the work function
C. Zero ✓ Correct
D. Equal to $h\nu_0$
Solution: The photon energy is just enough to free the electron with nothing left over.
Q16 — Work Function & Threshold · easy · theory
The work function of a metal is:
A. The minimum energy needed to free an electron from its surface ✓ Correct
B. The energy of the incident photon
C. The total energy of all the electrons in the metal
D. The kinetic energy of the fastest photoelectron
Solution: It represents the binding of the least tightly held electrons to the metal surface.
Q17 — Work Function & Threshold · easy · theory
The work function and threshold frequency are related by:
A. $\phi_0 = \dfrac{h}{\nu_0}$
B. $\phi_0 = h\nu_0^2$
C. $\phi_0 = \dfrac{\nu_0}{h}$
D. $\phi_0 = h\nu_0$ ✓ Correct
Solution: The threshold frequency is simply the work function expressed as a photon frequency.
Q18 — Work Function & Threshold · easy · theory
The work function of a metal is usually expressed in:
A. Electron volt ✓ Correct
B. Volt
C. Coulomb
D. Newton
Solution: One electron volt is $1.6 \times 10^{-19}\text{ J}$, a convenient size for atomic-scale energies.
Q19 — Work Function & Threshold · easy · numerical
A work function of $2\text{ eV}$ expressed in joule is:
A. $3.2 \times 10^{-19}\text{ J}$ ✓ Correct
B. $3.2 \times 10^{-18}\text{ J}$
C. $2 \times 10^{-19}\text{ J}$
D. $1.6 \times 10^{-19}\text{ J}$
Solution: $2 \times 1.6 \times 10^{-19} = 3.2 \times 10^{-19}\text{ J}$.
Q20 — Work Function & Threshold · easy · numerical
Two metals have work functions $2\text{ eV}$ and $4\text{ eV}$. Photoemission occurs more readily from:
A. Neither of them
B. Both equally
C. The metal of work function $2\text{ eV}$ ✓ Correct
D. The metal of work function $4\text{ eV}$
Solution: A lower work function means a longer threshold wavelength, so a wider range of light can eject electrons.
Q21 — Photons & Photon Energy · easy · theory
The energy of a photon of frequency $\nu$ is:
A. $\dfrac{h}{\nu}$
B. $\dfrac{\nu}{h}$
C. $h\nu$ ✓ Correct
D. $h\nu^2$
Solution: Equivalently $E = \dfrac{hc}{\lambda}$, so shorter wavelengths carry more energy per photon.
Q22 — Photons & Photon Energy · easy · theory
The rest mass of a photon is:
A. Infinite
B. Equal to the electron mass
C. Zero ✓ Correct
D. Dependent on its frequency
Solution: Only a massless particle can travel at exactly the speed of light, yet it still carries energy and momentum.
Q23 — Photons & Photon Energy · easy · theory
Photons travel in free space with a speed:
A. That increases with frequency
B. That depends on the intensity of the beam
C. Equal to $c$, independent of their frequency ✓ Correct
D. That decreases with frequency
Solution: All electromagnetic radiation propagates through vacuum at the same speed.
Q24 — Photons & Photon Energy · easy · theory
A photon is:
A. Negatively charged
B. Charged depending on its energy
C. Positively charged
D. Electrically neutral ✓ Correct
Solution: Being uncharged, a photon is undeflected by electric and magnetic fields.
Q25 — Photons & Photon Energy · easy · theory
The value of Planck's constant is approximately:
A. $1.6 \times 10^{-19}\text{ J}\cdot\text{s}$
B. $3 \times 10^8\text{ J}\cdot\text{s}$
C. $6.63 \times 10^{-34}\text{ J}\cdot\text{s}$ ✓ Correct
D. $6.63 \times 10^{-19}\text{ J}\cdot\text{s}$
Solution: Its extreme smallness is why quantum effects are invisible in everyday life.
Q26 — Photons & Photon Energy · easy · numerical
If the energy of a photon is doubled, its wavelength:
A. Doubles
B. Becomes four times
C. Halves ✓ Correct
D. Remains unchanged
Solution: $E = \dfrac{hc}{\lambda} \propto \dfrac{1}{\lambda}$.
Q27 — Photons & Photon Energy · easy · numerical
A photon of wavelength $1240\text{ nm}$ has energy:
A. $2\text{ eV}$
B. $1240\text{ eV}$
C. $0.5\text{ eV}$
D. $1\text{ eV}$ ✓ Correct
Solution: $E = \dfrac{1240}{1240} = 1\text{ eV}$.
Q28 — Photons & Photon Energy · easy · numerical
Two photons have wavelengths $400\text{ nm}$ and $800\text{ nm}$. The ratio of their energies is:
A. $4 : 1$
B. $1 : 2$
C. $2 : 1$ ✓ Correct
D. $1 : 4$
Solution: $E \propto \dfrac{1}{\lambda}$, so the shorter wavelength carries twice the energy.
Q29 — de Broglie Waves · easy · theory
The de Broglie wavelength of a particle of momentum $p$ is:
A. $hp$
B. $\dfrac{p}{h}$
C. $\dfrac{h}{p^2}$
D. $\dfrac{h}{p}$ ✓ Correct
Solution: Equivalently $\lambda = \dfrac{h}{mv}$ — the same relation that holds for a photon.
Q30 — de Broglie Waves · easy · theory
The de Broglie hypothesis states that:
A. Only electrons behave as waves
B. Waves cannot carry momentum
C. Only photons behave as particles
D. All moving matter has an associated wave ✓ Correct
Solution: Proposed in 1924, it extended wave-particle duality from radiation to matter.