(a) (i) Define atomic spectra.
(ii) Differentiate between emission spectra and absorption spectra.
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;
(iii) wavelength of the photon.
(c) (i) Differentiate between soft x-rays and hard x-rays.
(ii) Draw the circuit symbol for a p-n junction diode.
(iii) Give the reason for doping a semiconductor material.
Explanation
(i) Definition of atomic spectra
The emission of light from a substance when its excited electrons move to lower energy level.
OR
Distinct/separate bright lines of light of definite frequency/wavelength (emitted from vapourized atoms).
(ii) Differentiating between emission spectra and absorption spectra
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) (i) Calculation of energy of photon
DE = Ei – Ef
= -1.51 + 13.6
= 12.09 eV
= 12.09 x 1.6 x 10-19 J
= 1.934 x 10-18 J
(c) (i) Differentiating between soft x-rays and hard x-rays
Soft x-rays are those with longer wavelengths/lower penetrating power/ less energy while hard x-rays are those with shorter wavelengths/higher penetrating power/more energy.
(iii) Reason for doping a semiconductor material
To increase the electrical conductivity/reduce electrical resistivity of the semiconductor.