Physics (Essay) Paper 2 WASSCE (SC), .2019

Question 10

 

 

    1. Define atomic spectra.
    2. Differentiate between emission spectra and absorption spectra.

    1. The diagram above illustrates an electron transition from energy level n = 3 to n = 1. Calculate the:
    2. energy of the photon;
    3. frequency of the photon;
    4. wavelength of the photon
    1. Differentiate between soft x-rays and hard x-rays.
    2. Draw the circuit symbol for a p-n junction diode.
    3. Give the reason for doping a semiconductor material.

 

Observation

 

Part (a): Performance was poor. Many candidates failed to correctly define those concepts signifying complete ignorance.
Part (b): Performance was good as many candidates were able to respond correctly to this questions.
Part (c): Majority of the candidates correctly differentiated between soft x-rays and hard x-rays and also gave correct reason for doping a semiconductor material but many could not give the correct circuit symbol for a p-n junction diode.


The expected answer is
(a) (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.



(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.
(ii) Circuit symbol of p-n junction diode
(iii) Reason for doping a semiconductor material
To increase the electrical conductivity/reduce electrical resistivity of the semiconductor.