15 extra multiple-choice questions for Dual Nature of Radiation and Matter (12th Standard Physics, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Which method of electron emission involves the application of a strong external electric field to pull electrons from a metal surface?
- A. Thermionic emission
- B. Field emissionCorrect
- C. Photoelectric emission
- D. Secondary emission
Explanation. Field emission occurs when a powerful external electric field is applied to a metal, providing enough force to pull free electrons across the surface barrier.
Q2
In the observations of Hallwachs, what happened to a negatively charged zinc plate when it was irradiated with ultraviolet light?
- A. It became more negative
- B. It lost its negative chargeCorrect
- C. It remained unchanged
- D. It released positive ions
Explanation. When ultraviolet light hits a negatively charged zinc plate, photoelectrons are emitted, causing the plate to lose its negative charge and eventually become uncharged.
Q3
The minimum frequency of incident radiation required to trigger photoelectric emission for a specific metallic surface is known as the:
- A. Stopping frequency
- B. Cut-off wavelength
- C. Threshold frequencyCorrect
- D. Quantized frequency
Explanation. The threshold frequency is the characteristic minimum frequency for a given metallic surface below which no photoelectrons can be ejected, regardless of the light intensity.
Q4
How does the stopping potential change if the intensity of incident light is doubled while keeping the frequency constant?
- A. It is doubled
- B. It is quadrupled
- C. It is halved
- D. It remains the sameCorrect
Explanation. Stopping potential depends only on the frequency of the incident light and the nature of the material, not on the intensity or brightness of the radiation.
Q5
According to Einstein's quantum explanation, the energy of a single photon of frequency \(\nu\) is given by:
- A. \(E = \frac{1}{2} h \nu\)
- B. \(E = h \nu\)Correct
- C. \(E = h \lambda\)
- D. \(E = \frac{h}{\nu}\)
Explanation. Einstein proposed that light consists of discrete packets called photons, where the energy of each photon is calculated by multiplying Planck's constant by the radiation frequency.
Q6
According to de Broglie's hypothesis, if a particle's momentum increases, its associated matter wavelength will:
- A. Increase
- B. DecreaseCorrect
- C. Remain constant
- D. Become zero
Explanation. The de Broglie wavelength is inversely proportional to the momentum of a particle. Therefore, as the particle's momentum increases, its associated wavelength gets shorter.
Q7
The de Broglie wavelength of an electron accelerated through a potential difference of \(V\) volts is approximately given by which expression?
- A. \(\lambda = \frac{12.27}{\sqrt{V}}\) \AACorrect
- B. \(\lambda = \frac{1.227}{\sqrt{V}}\) \AA
- C. \(\lambda = 12.27 \sqrt{V}\) \AA
- D. \(\lambda = \frac{\sqrt{V}}{12.27}\) \AA
Explanation. By substituting the mass and charge of an electron into the de Broglie equation, the wavelength simplifies to a formula involving the square root of the voltage.
Q8
The Davisson-Germer experiment was historically significant because it experimentally verified:
- A. The particle nature of light
- B. The wave nature of material particlesCorrect
- C. The existence of X-rays
- D. The quantization of electric charge
Explanation. This experiment demonstrated that electron beams undergo diffraction when hitting a crystal, proving that material particles in motion possess wave-like properties as de Broglie hypothesized.
Q9
In an electron microscope, the components used to focus the electron beam are known as:
- A. Optical glass lenses
- B. Polished silver mirrors
- C. Electric or magnetic fieldsCorrect
- D. Diffraction gratings
Explanation. Because electrons are charged, their paths can be manipulated and focused using carefully designed electromagnetic or electrostatic fields, which serve as lenses for the beam.
Q10
Which of the following occurs during the production of X-rays in a Coolidge tube?
- A. Slow electrons collide with gas molecules
- B. Fast electrons are suddenly decelerated by a targetCorrect
- C. Protons are emitted from a hot filament
- D. Light is converted into high-energy electrons
Explanation. When high-speed electrons strike a metal target, they lose kinetic energy through deceleration, which is then emitted as highly penetrating electromagnetic X-ray radiation.
Q11
In a continuous X-ray spectrum, the minimum wavelength (cut-off wavelength \(\lambda_0\)) is determined solely by the:
- A. Atomic number of the target
- B. Intensity of the electron beam
- C. Accelerating potential differenceCorrect
- D. Temperature of the target
Explanation. According to the Duane-Hunt formula, the shortest wavelength in the continuous spectrum is determined solely by the voltage applied to accelerate the electrons.
Q12
The sharp peaks observed in characteristic X-ray spectra are produced by:
- A. The thermal heating of the anode
- B. Electronic transitions between inner atomic shellsCorrect
- C. Scattering of electrons by air molecules
- D. Reflection of electrons from the glass tube
Explanation. These peaks arise when a high-speed electron knocks out an inner-shell electron of a target atom, causing an electron from a higher level to fall into the vacancy.
Q13
A device that converts incident light energy into electrical energy using the principle of the photoelectric effect is a:
- A. Thermocouple
- B. Photoelectric cellCorrect
- C. Galvanometer
- D. Transformer
Explanation. Photoelectric cells use photosensitive materials to generate an electric current or voltage when exposed to light, transforming optical energy into electrical signals.
Q14
The work function of a metal surface is most commonly measured in which of the following units?
- A. Watt
- B. Tesla
- C. Electron volt (eV)Correct
- D. Ohm
Explanation. The electron volt (eV) is the standard unit used to describe the small amount of energy required for an electron to escape from a metal surface.
Q15
The conclusion that light propagates as a wave but interacts with matter as a stream of particles is described as:
- A. Wave-particle dualityCorrect
- B. Electromagnetic induction
- C. The uncertainty principle
- D. Wavefront division
Explanation. Duality describes the complementary nature of radiation and matter, where both exhibit wave and particle characteristics depending on the specific physical phenomenon observed.
