Question

A hot filament liberates an electron with zero initial velocity. The anode potential is $1200\,V$. The speed of the electron when it strikes the anode is

• A. $1.5 \times 10^5 \,ms^{-1}$
• B. $2.5 \times 10^6 \,ms^{-1}$
• C. $2.1 \times 10^7 \,ms^{-1}$
• D. $2.5 \times 10^8 \,ms^{-1}$

Answer 1

Answer: (C)

$\frac{1}{2} m v^{2}=V q$
$v=\sqrt{\frac{2 V q}{m}}$
$=2.1 \times 10^{7} ms ^{-1}$