(a) Define ionization potential.
(b)(i) State the three types of emission spectra.
(ii) Name one source each which produces each of the spectra stated in (b)(i).
(c) In an x-ray tube, electrons are accelerated the target by a potential difference of 80 A Calculate the:
(i) speed of the electron;
ii) threshold wavelength of the electron. [h=6.6 x 10(^{-34}) Js; e = 1.6 x 10(^{-19}) C; Me = 9.1 x 10(^{-31})
d) An x-ray photon of frequency 4.5 x 10(^{-18}) strikes an. electron, assumed to be at rest. If t electron absorbs all the photon energy, calculate the speed acquired by the electron. [ h = 6.6 x 10(^{-34}) Js; Me = 9.1 x 10(^{-31}) kg ]
Explanation
a) Ionization potential V is the potential energy required to remove an electron from an atom completely to infinity from ground state.
(b)(i) The three types of emission are
– band spectrum
– continuous spectrum and
– line spectrum.
(ii) Sources of each emmision spectrum are:
– Band spectrum
– from molecules or carbon(IV) oxides in a discharge tube.
– Continuous spectrum
– from sun, solids and liquids.
– Line spectrum
– from atoms in gases such as hydrogen or neon in a discharge tube.
(c)(i) eV =(frac{1}{2} mV^2)
v = (sqrt{frac{2 times 1.6 times 10^{-19} times 80 times 10^3}{9.1 times 10^{-31}}})
= (sqrt{2.81 times 10^{16}})
= 1.68 x 10(^8 ms^{-1})
(ii) (pi = frac{h}{mv} = frac{6.6 times 10^{-31}}{9.1 times 10^{-31} times 1.68 times 10^8})
= 4.32 x 10(^{-12})m
(d) hf = (frac{1}{2}mv^2)
6.6 x 10(^{-34} times 4.5 times 10^{18})
= (frac{1}{2} times 9.1 times 10^{-31} times v^2)
(v^2 = frac{2.97 times 10^{-15}}{4.55 times 10^{-3}})
(v^2 = sqrt{6.53 times 10^{15}})
= 8.08 x 10(^7 ms^{-1})