Question

A cathode emits $1.8\times {10}^{14}$ electrons per second when heated. When $400V$ is applied to anode all the emitted electrons reach the anode. The charge on electron is $1.6\times {10}^{-19}C$ The maximum anode current is

• A. $2.7\mu A$
• B. $29\mu A$
• C. $72\mu A$
• D. $29mA$

Answer 1

Answer: (B)

$29\mu A$

As we know,

$i=\frac{Q}{t}=\frac{ne}{t}=1.8\times {10}^{14}\times 1.6\times {10}^{-19}=28.8\times {10}^{-6}A$

$=29\mu A$