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.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 (Eg)c, (Eg)sir and (Eg)Ge.
(a) (Eg)Sir < (Eg)Ge. < (Eg)C
(b) (Eg)C < (Eg)Ge. < (Eg)sir
(c) (Eg)C < (Eg)sir. < (Eg)Ge
(d) (Eg)C < (Eg)sir. < (Eg)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 lc 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.
current Ic for a transistor action, the emitter junction is forward biased and collector junction is reverse 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.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 ?
Sol. (a) In (a), the out put of NOR gate is made input for NOT gate. Then Boolean expression is
Sol. In (a), we have NAND gate, with one input A and one output Y. The Boolean expression is

Sol. The Boolean expression for the given circuit is
It means OR gate is created. Truth table of this gate is shown in adjoining table (b).
