(a) (i) Define atomic spectra.
(ii) Differentiate between emission spectra and absorption spectra.
(b)
The diagram above illustrates an electron transition from energy level n = 3 to n = 1. Calculate the:
(i) energy of the photon
(ii) frequency of the photon
(ii) wavelength of the photon [h = 6.6 x 10\(^{-34}\)J s, c = 3.0 x 10\(^8\) ms\(^{-1}\); 1 ev = 1.6 x 10\(^{-19}\) J]
c)(i)Differentiate between soft x-rays and hard x-rays
(ii) Draw the circuit symbol for a p-n junction diode.
(iiii) Give the reason for doping a semiconductor material
Explanation
(a) The emission of light from a substance when its excited electrons move to a lower energy level.
OR
Distinct/separate bright lines of light of definite frequency/wavelength (emitted from vapourised atoms)
(ii) Emission spectra is the pattern of light displayed when electrons jump from a higher energy level to a lower energy level, while absorption spectra is the displayed pattern of wavelengths absorbed by the gas.
(b) \(\Delta\)E = E\(_i\) - E\(_f\)
= -1.51 + 13.6
= 12.09 eV
= 12.09 x 1.6 x 10\(^{-19}\) J
= 1.934 x 10\(^{-18}\) J
(ii) \(\Delta\)E- hf
f = \(\frac{\Delta E}{h}\) = \(\frac{1.934 \times 10^{-18}}{6.6 \times 10^{-34}}\)
f = 2.93 x 10\(^{15}\)Hz
(ii) c = f\(\lambda\)
\(\lambda\) = \(\frac{3 \times 10^8}{2.93 x 10^{13}}\)
= 1.023 x 10\(^{-7}\)m
(c) (I) Soft x-rays are those with longer wavelengths/lowNer penetrating/less energy while hard x-rays are those with shorter wavelengths/higher penetrating power more energy.
(iii) To increase the electrical conductivity/reduce electrical resistivity of the semiconductor.