NCERT 12 Physics Semiconductor Electronics Materials, Devices And Simple Circuits Chapter 14 Exercise

Q.1. In n- type which of the following statement is true:

(a) Electrons are majority carriers and trivalent atoms are the dopants

(b) Electrons are minority carriers and pentavalent atoms are the dopants

(c) Holes are minority carriers and pentavalent atoms are the dopants

(d) Holes are majority carries and trivalent atoms are the dopants

Q.2. Which of the statements given in Q.1 is true for p-type semiconductors.

Q.3. Carbon, silicon and germanium have four valence electrons each. These are characterized by valence and conduction bands separated by energy band gap respectively equal (E_g)c, (E_g)_sir  and (E_g)_Ge.

(a) (E_g)_Sir < (E_g)_Ge. < (E_g)_C

(b) (E_g)_C < (E_g)_Ge. < (E_g)_sir

(c) (E_g)_C < (E_g)_sir. < (E_g)_Ge

(d) (E_g)_C < (E_g)_sir. < (E_g)_Ge

Q.4. In an unbiased p-n junction, holes diffuse from the p-region to n-region because

(a) free electrons in the n-region attract them

(b) they move across the junction by the potential difference

(c) hole concentration in p-region is more as compared to n-region

(d) all the above.

Q.5. When a forward bias is applied to p-n junctions, it

(a) free electrons in the n-region attract them

(b) they move across the junction by the potential difference

(c) hole concentration in p-region is more as compared to n-region

(d) all the above.

Q.6. For a transistor action, which of the following statements are current.

(a) collector current is equal to the sum of base current and emitter current.

(b) The input resistance depends upon the current l_c in the transistor.

(c) The emitter junction is forward biased and collector is reverse biased.

(d) Both the emitter junction as well as the collector junction are forward biased.

Q.7. For transistor amplifier, the voltage gain (a) remains constant for all frequencies

(b) is high at high and low frequencies and constant in the middle frequency range

(c) is low at high and low frequencies and constant at mid frequencies

(d) None of the above.

Q.8. In half wave rectifier, what is the output frequency if the input frequency is 50 Hz. What is the output frequency of a full-wave rectifier for the same input frequency.

Q.9. For a common emitter amplifier, the audio signal voltage across the collector resistance of 2 KΩ is 2 V. Suppose the current amplification factor of the transistor is 100, find the input signal voltage and base current, if the base resistance is 1 k Ω.

Q.10. Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of 10 and the second has a voltage gain of 20. If the input signal is 0.01 V, calculate the output a. c. signal.

Q.11. A p-n junction is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 600 nm ?

Q.12. The number of silicon atoms per m³ is 5 × 10²⁸ This is doped simultaneously with 5 × 10²²  atoms per m³ of Arsenic and 5 × 10²⁰ per m³ atoms of Indium. Calculate the number of electrons and holes. Given that n_i = 1.5 × 10¹⁶ m^-3 is the material n-type or p- type ?

Q.13 In an intrinsic semiconductor the energy gap  is 1.2 e V. Its hole mobility is much smaller than electron mobility and independent of temperature. What is the ratio between conductivity at 600 K and 300 K ? Assume that the temperature dependence intrinsic concentration  is given by

Q.14. In a p-n junction diode, the current I can be expressed

Where I₀ is called the reverse saturation current, V is the voltage across the diode and is positive for forward bias and negative for reverse bias, and I is the current through the diode,  is the Boltzmann constant (8.6× 10^-5e V/K)  and T is the absolute temperature. If for a given diode, I₀ = 5 × 10^-12 A and T = 300 k then (a) What will be the forward current at a forward voltage of 0.6 V ?

(b) What will be the increase in the current if the voltage across the diode is increased to 0.7 V ?

(c) What is dynamic resistance ?

(d) What will be the current if reverse bias voltage changes from 1 V to 2 V ?

Q.15. You are given two circuits as shown in (a) and (b), Show that circuit (a) acts as OR gate while the circuit (b) acts as AND gate.

Q.16 Write the truth table for a NAND gate as given in. Hence identify the exact logic operation carried out by this circuit.

Q.17. You are given two circuits as sown in (a) and (b) which consists of NAND gates. Identify the logic operation carried out by the two circuits.

Q.18. Write the truth table for circuit given in (a) below of NOR gates and identify the logic operation (OR, and NOT) which this circuit is performing.

Q.19. Write the truth table for the circuit given in (a) and (b), consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by two circuits.