The specific charge (e/m) of an electron was first measured by:
A. Thomson
B. Millikan
C. Bohr
D. Rutherford
Answer: Option A
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:
Doppler effect: apparent change in frequency due to relative motion. Siren pitch changes as it approaches/recedes. Echo is reflection. Bending is diffraction. Fusion is nuclear reaction.
Explanation:
Concave mirror: real, inverted image forms when object beyond focal point (u > f). Between pole and focus: virtual, erect image. At focus: image at infinity. Memory aid: 'Concave: object beyond F ⇒ real image; within F ⇒ virtual'. Ray optics concept frequently tested to verify mirror image formation understanding in competitive exams.
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