Electronics Devices

1. Solar cells use _____ to turn light into energy.(Ans- Semiconductors,Explanation-When light hits a solar cell, semiconductors such as silicon absorb the light and eventually transform it into an electrical current.)

2. Silicon works as a semiconductor because: (Ans- Added impurities allow electrons to move freely,Explanation-In its ordinary, crystalline form, silicon is not a good conductor because none of its electrons can move freely. But if you add tiny amounts of impurities, electrons can move, creating a tiny current.)

3. When you combine P-type and N-type silicon in a solar cell: (Ans- Electrons at the NP junction eventually form a barrier, Explanation- It may seem like all the free electrons from N-type silicon would make a mad dash for the available empty spaces in P-type silicon. In reality, the electrons near the borders of each type mix, gradually creating an effective barrier -- an electric field.)

4. Drift current in the semiconductors depends upon:: (a) only the electric field. (b) only the carrier concentration gradient. (c) both the electric field and the carrier concentration (d) both the electric field and the carrier concentration gradient.
Drift current  Id=qnμ_nE 
It depends upon Electric field E and carrier concentration n

Hence (C) is correct option.

5. A silicon PN junction is forward biased with a constant current at 
room temperature. When the temperature is increased by 10ºC, the 
forward bias voltage across the PN junction
(A) increases by 60 mV
(B) decreases by 60 mV
(C) increases by 25 mV
(D) decreases by 25 mV

For every 1ºc  increase in temperature, forward bias voltage across
diode decreases by 2.5 mV. Thus for 10ºc  increase, there us 25 mV
decreases.

Hence (D) is correct option.

6. Compared to a p-n junction with  N_A =N_D =10¹⁴ /cm³ which 
one of the following statements is TRUE for a p-n junction with 
  N_A =N_D =10²⁰ /cm³ ?
(A) Reverse breakdown voltage is lower and depletion capacitance is 
lower
(B) Reverse breakdown voltage is higher and depletion capacitance is 
lower
(C) Reverse breakdown voltage is lower and depletion capacitance is 
higher
(D) Reverse breakdown voltage is higher and depletion capacitance is 
higher

Breakdown voltage VB α 1/ N_A N_D

So, breakdown voltage decreases as concentration increases
Depletion capacitance

Thus  C={ e€_sN_AN_D / 2(Vbi+Vr)( N_A +N_D)}^1/2  

C α N_A N_D

Depletion capacitance increases as concentration increases

Hence (C) is correct option

7.