An electron is accelerated from rest through a potential difference V. This electron experiences a force F in a uniform magnetic field. On increasing the potential difference to V', the force experienced by the electron in the same magnetic field becomes 2F. Then, the ratio `(V'//V)` is equal to

Options

A. `4//1`
B. `2//1`
C. `1//2`
D. `1//4`

Answer

A

Explanation

`K=1/2mv^2=eV or v=sqrt((2eV)/m)`
Also, `F=eB=e[sqrt((2eV)/m)]xxB`
Therefore, `F/(2F)=sqrt((V_1)/(V_2))=sqrt(V/V')`
`:. (V')/(V)=4/1`.