CBSE CLASS XII PHYSICS
Solids and Semiconductors
One mark questions with answers
Q1. Draw a labelled diagram to show the circuit symbols of an N-P-N transistor.
Q2. What kinds of biasing are required to the collector and base of a transistor in a common emitter amplifier?
Ans2. The input circuit i.e base emitter circuit is forward biased and the output circuit i.e collector emitter circuit is reverse biased so the current flows through D2 only.
Q3. What is a solar cell and where is it used?
Ans3. When P-region or N-region of P-N junction diode is made very thin [incident energy is not greatly absorbed] the junction diode is called solar cell. These are used in street lights, satellites etc.
Q4. What can be the cause of sudden increase in the reverse current through junction diode?
Ans4. When the reverse voltage is increased beyond a certain value (Zener voltage or breakdown voltage) then large number of covalent bonds are broken. It results into large electron-hole pairs which diffuse through the junction and hence there is a sharp rise in the reverse current.
Q5. Can we put pure semiconductors to any use?
Ans5. No, because the conductivity of semiconductors is low and variable both.
Q6. Write a relation between ni, ne and nh for pure semiconductor and impure semiconductor where symbols have their usual meaning.
Ans6. nenh = ni2 is valid for both pure and impure semiconductor.
Q7. Is valence band completely filled up in all conductors?
Ans7. No, it is half filled in sodium type and is completely filled up in magnesium and zinc type.
Q8. Write the condition under which forward current flows through the junction diode.
Ans8. e(φ/kT) > > 1 because the junction diode will be in forward bias and 'k' is the Boltzmann's constant.
Q9. Does P-N junction diode act like a linear device under some condition?
Ans9. Yes, the junction diode behaves like a linear device beyond the knee voltage.
Q10. At high temperature, which semiconductor is...