Question

Which of the following have highest specific charge?

• A. Positron
• B. Proton
• C. He
• D. None of these

Answer 1

Answer: (A)

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.