Question

An electron initially at rest, is accelerated through a potential difference of 200 volt, so that it acquires a velocity ${8.4 \times 10^6 m s^{-1}}$, the value of $e/m$ of electron will be

• A. ${1.76 \times 10^{11} C kg^{-1}}$
• B. ${3.76 \times 10^{12} C kg^{-1}}$
• C. ${4 \times 10^{11} C kg^{-1}}$
• D. ${0.76 \times 10^{11} C kg^{-1}}$

Answer 1

Answer: (A)

${1.76 \times 10^{11} C kg^{-1}}$

Answer 2

Maximum kine $KE_{max} = eV$
or $\frac{1}{2} mv^2 = eV$
$= \frac{1}{2} \frac{(8.4 \times 10^6)^2}{2 \times 10^2} = 1.764 \times 10^{11} \,{ C \, kg^{-1}}$