21. Radio carbon dating is done by estimating in the specimen :
(a) The amount of ordinarily carbon still present
(b) The radio of the amounts of 6C14 + 6C12
(c) The amount of radio carbon still present
(d) None of these
22. The specific charge (e/m) of the electron is approximately :
(a) 20 × 102 C/kg
(b) 40 × 1012 C/kg
(c) 1.8 × 1011 C/kg
(d) 0.9 × 1011 C/kg
23. The constituent particles of a nucleus are :
(a) electrons, protons and neutrons
(b) α-particles and β-particles
(c) protons and neutrons
(d) electrons and protons
24. The value of 1 electron volt = …………… J.
(a) 1.6 x 1019 J
(b) 1.6 x 10–19 J
(c) 1.6 x 1020 J
(d) 1.6 x 10–20 J
25. which of the following transition in hydrogen atoms emits Photon of highest frequency ?
(a) n=2 to n=6
(b) n=1 to n=2
(c) n=2 to n=1
(d) n=6 to n=2
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