Question

An electron is allowed to freely move between a pair of parallel plates that have a $1.5$ volt potential difference. The electron starts at the negative plate. The velocity of the electron as it strikes the positive plate is most nearly:

• A. $7.3\times {10}^{-8}m/s$
• B. $7.3\times {10}^{-5}m/s$
• C. $7.3\times {10}^{5}m/s$
• D. $7.3\times {10}^{8}m/s$
• E. $7.3\times {10}^{11}m/s$

Answer 1

The correct option is C $7.3\times {10}^{5}m/s$

When electron is accelerated by a potential difference of $1.5V$ , its kinetic energy would be $1.5eV$ ,

so , $K=1.5eV=1.5\times 1.6\times {10}^{-19}=2.4\times {10}^{-19}J$ ,

now , $K=\frac{1}{2}m{v}^2$ , where $m=9.1\times {10}^{-31}kg$ (mass of the electron)

or $2.4\times {10}^{-19}=\frac{1}{2}\times 9.1\times {10}^{-31}\times v^2$ ,

or $v^2=0.527\times {10}^{12}$

or $v=7.3\times {10}^{5}m/s$