A) Positron
B) Proton
C) He
D) None of these
Correct Answer: A
Solution :
Key Idea: Specific charge is equal to ratio of charge to mass. If charge is q and mass m then the ratio of charge (q) to mass (m) is known as specific charge. For positron, \[{{m}_{e}}=9.1\times {{10}^{-31}}kg,e=1.6\times {{10}^{-19}}C\] \[\frac{e}{m}=\frac{1.6\times {{10}^{-19}}}{9.1\times {{10}^{-31}}}\] \[=1.75\times {{10}^{11}}Ck{{g}^{-1}}\] For proton, \[{{m}_{p}}=1.67\times {{10}^{-27}}kg,e=1.6\times {{10}^{-19}}C\] \[\frac{e}{m}=\frac{1.6\times {{10}^{-19}}}{1.67\times {{10}^{-27}}}\] \[=9.58\times {{10}^{7}}Ck{{g}^{-1}}\] For helium, \[{{m}_{He}}=6.6\times {{10}^{-27}}kg,{{q}_{He}}=2\times 1.6\times {{10}^{-19}}C\] \[\frac{e}{m}=\frac{2\times 1.6\times {{10}^{-19}}}{6.6\times {{10}^{-27}}}=4.84\times {{10}^{7}}Ck{{g}^{-1}}\] Hence, positron has highest specific charge.
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