An x-ray tube is operated at `20 kV` and the current through the tube is `0*5 mA`. Find (a) the number of electrons hitting the target per second, (b) the energy falling on the target per second as the kinetic energy of the electrons and © the cutoff wavelength of the X-rays emitted.

Explanation

(a) `i = ne = 0*5 xx 10 ^ (-3) A`
or, `n = (0*5 xx10 ^(-3)A)/( 1*6 xx 10^(-19)C )= 3*1 xx 10^(15)`.
(b) The kinetic energy of an electron reaching the target is `K= eV`. The energy falling on the target per second ,
`=n eV = iV = (0.5 xx 10 ^ (-3)A) xx (20 xx 10 ^(3) V)`
`10 J s^(-1)`
(c) `(hc)/(lambdamin)= eV`
or, `lambdamin = (hc)/(eV)`
`(1242 eV nm)/(e(20xx10^(3) V)) = (0.62 nm)`.