Question

An X-ray tube operating at 20 kV shows a current 1 mA. Assuming efficiency 1%. Find the number of X-ray photons emitted per second.

• A. $5.25\ast {10}^{13}$
• B. $6.25\ast {10}^{13}$
• C. $6.25\ast {10}^{15}$
• D. $5.25\ast {10}^{15}$

Answer 1

Answer: (B)

$6.25\ast {10}^{13}$

$Current=I=charge/s$
$I=1mA=1mC/s$

No. of electrons = $\frac{{10}^{-3}}{e}=\frac{1}{1000e}$

Efficiency of knocking photoelectons = 0.01
Hence
No. of photons emitted = $0.01\times \frac{1}{1000e}=6.25\times {10}^{13}$

So, the answer is option (B).