CBSE Class 12 Physics VBQs Semiconductor Devices A

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CBSE Class 12 Physics VBQs Semiconductor Devices A Based on CBSE and NCERT guidelines. Value based questions are now being given in exams to promote morals and values in students, Students should read and understand the following VBQs to get better understanding and score good marks in exams


Q1. A pure semiconductor germanium or silicon, free of every impurity is called intrinsic semiconductor. At room temperature, a pure semiconductor has a very small number of current carries (electrons and holes). Hence its conductivity is low.
When the impurity atoms of valence five or three are doped in a pure semiconductor, we get respectively n-type or p-type extrinsic semiconductor. In case of a doped semiconductor. ne nh = ni2; where ne and nh are the number density of electrons and holes respectively and ni is the number density of intrinsic charge carriers in a pure semiconductor. The conductivity of extrinsic semiconductor is much higher than that of intrinsic semiconductor.

Read the above passage and answer the following questions:

(i) Name two materials to be doped in pure semiconductor of silicon to get (a) p-type semiconductor (b) n-type semiconductor
(ii) What do you learn from the above study?

Q2. Rohan was studying in a science college and was staying with his grandfather. One day, the old torch which was being used by Rohan’s grandfather stopped working. He asked Rohan to purchase a new torch for him. Rohan himself made a torch using LED with a small recharge battery and give it to his grandfather as a gift. Rohan explained the advantages of LED over a bulb. Rohan’s grandfather was very happy.

Read the above passage and answer the following questions:

(i) What is LED? Name the two materials used in making LED, whose light falls in the visible region.
(ii) Why LED is a better choice than a bulb in torch?
(iii) What do you think about the attitude of Rohan towards his grandfather?

Q3. Manoj wanted to do social work during his vacations. He visited a remote village where there was no electricity. He made up his mind to help the villagers for getting solar panels. For this he educated the villagers about the technology and uses of solar panels. He requested the villagers to apply for the same to the government as the same was given to the villagers on subsidised rates. Villagers agreed and apply for the solar panels. They got the same from the government at reduced price. When the solar panels started working, the villagers were very happy.

Read the above passage and answer the following questions:

(i) What is a solar panel?
(ii) What is the basic principle of working of a solar panel?
(iii) What are the basic values you assess in Manoj?


Ans1. (i) (a) The doping of pure silicon with boron or aluminium will give us p-type semiconductor
(b) The doping of pure silicon with arsenic or phosphorous will give us n-type semiconductor.

(ii) From the above study, we find that to get better output current, pure semiconductor has to be doped with suitable impurity atoms. Similarly, in day to day life, the appearance of right kind of persons (leaders) in society can improve their lot.

Ans2.(i) LED stands for light emitting diode. The following materials are used in making LEDs whose light falls in the visible region;
(a) Gallium-phosphide (GaP) – giving red or green light
(b) Gallium-arsenide phosphide (GaAsP) – giving red or yellow light.

(ii) LED is better than conventional bulbs the torch with LED is handy and light. It gives the intense light and consumes less power.
(iii) Rohan had a great love and respect for his grandfather. He proved it by making a torch for him using new technology. By this act, Rohan earned more love and affectionate from his grandfather.

Ans3. (i) Solar panel is a panel having large number of solar cells fitted by side on it.

(ii) Solar cell is basically a solar energy converter. It is a p-n junction device which converts solar energy into electrical energy. If this energy is stored in a capacitor, it can be used for glowing bulbs.

(iii) Manoj displayed his will to do something for society. Through his shear efforts, he got electricity within the reach of villagers, who were suffering otherwise. The work of Manoj was highly appreciated by the villagers.


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