The specific charge (e/m) of an electron was first measured by:
A. Rutherford
B. Bohr
C. Thomson
D. Millikan
Answer: Option C
Solution (By JKSSB Mock Tests)
J. J. Thomson measured the specific charge (e/m) of electrons in 1897 using cathode ray tube experiments with electric and magnetic fields. Millikan later measured the charge e (oil drop experiment), allowing mass calculation. Rutherford discovered nucleus; Bohr developed atomic model. Memory aid: 'Thomson = e/m; Millikan = e'. This history-based question tests knowledge of experimental physics milestones, frequently appearing in competitive exams. Always link scientists to their specific measurements: Thomson (e/m), Millikan (e), Chadwick (neutron).
Explanation:
G = 6.67 × 10⁻¹¹ N m²/kg² in SI, and 6.67 × 10⁻⁸ dyne cm²/g² in CGS. Both are correct. Important constant, measured by Cavendish. g is acceleration due to gravity, different.
Which scientific instrument is used specifically for measuring very high temperatures, such as the surface temperature of the Sun or inside a furnace, from a distance?
Explanation:
A pyrometer is a non-contact thermometer used to measure high temperatures. It operates on the principle of thermal radiation (Stefan-Boltzmann law or Wien's law), measuring the intensity or spectrum of electromagnetic radiation emitted by the extremely hot object. A cryometer measures very low temperatures, and a calorimeter measures heat capacity.
Explanation:
Power P = V²/R => R = V²/P = 200²/100 = 40000/100 = 400 Ω. Also current I = P/V = 0.5 A, R = V/I = 200/0.5 = 400 Ω. Use P = V²/R for direct calculation.
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