Match List-I with List-II. List-II gives the value of each quantity in the unit stated in List-I.
| List-I | List-II |
|---|---|
| (A) Specific charge \(e/m\) of the electron, in \(\mathrm{C\,kg^{-1}}\) | (I) Of the order of \(10^{8}\) |
| (B) Electric field needed for field emission from a metal, in \(\mathrm{V\,m^{-1}}\) | (II) Of the order of \(10^{-9}\) or less |
| (C) Time taken by photoelectric emission to start after the light falls on the metal, in s | (III) \(1.76\times10^{11}\) |
| (D) Planck’s constant, in J s | (IV) \(6.626\times10^{-34}\) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(III), (B)-(I), (C)-(II), (D)-(IV)
(A) Specific charge \( e/m \) of the electron — This matches (III). J. J. Thomson first measured this charge to mass ratio for the cathode-ray particles.
(B) Electric field needed for field emission — This matches (I). Such a strong field pulls electrons out of a metal, as in a spark plug.
(C) Time taken by photoelectric emission to start — This matches (II). Emission starts almost at once, even when the light is very dim.
(D) Planck’s constant — This matches (IV). Millikan found \( h \) from the slope of the stopping potential against frequency line.
NCERT (2026-27):
Introduction – “… J. J. Thomson was the first to determine experimentally the speed and the specific charge [charge to mass ratio (e/m)] of the cathode ray particles. … The presently accepted value of e/m is 1.76 × 1011 C/kg. …”
Electron Emission – “(ii) Field emission: By applying a very strong electric field (of the order of 108 V m–1) to a metal, electrons can be pulled out of the metal, as in a spark plug.”
Effect of frequency of incident radiation on stopping potential – “… It is now known that emission starts in a time of the order of 10–9 s or less.”
Einstein’s Photoelectric Equation: Energy Quantum of Radiation – “… He measured the slope of the straight line obtained for sodium … Using the known value of e, he determined the value of Planck’s constant h. This value was close to the value of Planck’s contant (= 6.626 × 10–34J s) determined in an entirely different context. …”