IndiaBix: Electronics Devices and Circuits Section 2

b

A Schottky diode clamp is used along with switching BJT for reducing the power dissipation reducing the switching time increasing the value of β reducing the base current

b

A diode is operating in forward region and the forward voltage and current are v = 3 + 0.3 sin ωt (volts) and i = 5 + 0.2 sin ωt (mA). The average power dissipated is 15 mW about 15 mW 1.5 mW about 1.5 mW

a

An incremental model of a solid state device is one which represents the ac property of the device at desired operating point dc property of the device at all operating points complete ac and dc behaviour at all operating points ac property of the device at all operating points

b

An one sided abrupt junction has 1021/m3 of dopants on the lightly doped side, zero bias voltage and a built-in potential of 0.2 V. The depletion width of abrupt junction.(q = 1.6 x 10-19 C, εr =16, ε0 = 8.87 x 10-12 F/m) is 0.036 nm 0.6 μm 3 mm 1.5 mm

b

As temperature increases the forbidden energy gap in silicon and germanium increase the forbidden energy gap in silicon and germanium decrease the forbidden energy gap in silicon decreases while that in germanium decreases the forbidden energy gap in silicon increases while that in germanium decreases

d

Assertion (A): A decrease in temperature increases the reverse saturation current in a p-n diode. Reason (R): When a diode is reverse biased surface leakage current flows. Both A and R are true and R is correct explanation of A Both A and R are true but R is not a correct explanation of A A is true but R is false A is false but R is true

a

Assertion (A): Silicon is preferred over germanium in manufacture of semiconductor devices. Reason (R): Forbidden gap in silicon is more than that in germanium. Both A and R are true and R is correct explanation of A Both A and R are true but R is not a correct explanation of A A is true but R is false A is false but R is true

a

Assertion (A): Two transistors one n-p-n and the other p-n-p are identical in all respects (doping, construction, shape, size). The n-p-n transistor will have better frequency response. Reason (R): The electron mobility is higher than hole mobility. Both A and R are true and R is correct explanation of A Both A and R are true but R is not a correct explanation of A A is true but R is false A is false but R is true

c

At room temperature a semiconductor material is perfect insulator conductor slightly conducting any of the above

b

Calculate the resistivity of n-type semiconductor from the following data, Density of holes = 5 x 1012 cm-3. Density of electrons = 8 x 1013 cm-3, mobility of conduction electron = 2.3 x 104 cm2/ V-sec and mobility of holes = 100 cm2/V-sec. 0.43 Ω-m 0.34 Ω-m 0.42 Ω-m 0.24 Ω-m

d

Compared to bipolar junction transistor, a JFET has lower input impedance high input impedance and high voltage gain higher voltage gain high input impedance and low voltage gain

b

For BJT transistor. The maximum power dissipation is specified as 350 mW if ambient temperature is 25°C. If ambient temperature is 60°C the maximum power dissipation should be limited to about 100 mW 250 mW 450 mW 600 mW

a

For an n-channel enhancement type MOSFET, if the source is connected at a higher potential than that of the bulk (VSB > 0), the threshold voltage VT of the MOSFET will remain unchanged decrease change Polarity increase

c

If the reverse voltage across a p-n junction is increased three times, the junction capacitance will decrease will increase will decrease by an approximate factor of about 2 will increase by an approximate factor of about 2

a

In a bipolar junction transistor the base region is made very thin so that recombination in base region is minimum electric field gradient in base is high base can be easily fabricated base can be easily biased

c

In a piezoelectric crystal, application of a mechanical stress would produce plastic deformation of the crystal magnetic Dipoles in the crystal electric polarization in the crystal shift in the Fermi level

c

In a piezoelectric crystal, applications of a mechanical stress would produce plastic deformation of the crystal magnetic dipoles in the crystal electrical polarization in the crystal shift in the Fermi level

a

In all metals conductivity decreases with increase in temperature current flow by electrons as well as by holes resistivity decreases with increase in temperature the gap between valence and conduction bands is small

a

In an n channel JFET ID, IS and IG are considered positive when flowing into the transistor ID and IS are considered positive when flowing into transistor and IG is considered positive when flowing out of it ID, IS, IG are considered positive when flowing out of transistor IS and IG are considered positive when flowing into transistor and ID is considered positive when flowing out of it

d

In which of the following is the width of junction barrier very small? Tunnel diode Photo diode PIN diode Schottky diode

b

Junction temperature is always the same as room temperature. True False

b

Measurement of Hall coefficient enables the determination of recovery time of stored carrier type of conductivity and concentration of charge carriers temperature coefficient and thermal conductivity Fermi level and forbidden energy gap

b

Photo electric emission can occur only if wave length of incident radiation is equal to threshold value wave length of incident radiation is less than threshold value frequency of incident radiation is less than threshold frequency none of the above

b

The Hall constant in Si bar is given by 5 x 103 cm3/ coulomb, the hole concentration in the bar is given by 105/cm3 1.25 x 1015/cm3 1.5 x 1015/cm3 1.6 x 1015/cm3

b

The amount of photoelectric emission current depends on the frequency of incident light. True False

d

The carriers of n channel JFET are free electrons and holes holes free electrons or holes free electrons

b

The concentration of minority carriers in a semiconductor depends mainly on the extent of doping temperature the applied bias none of the above

c

The depletion layer around p-n junction in JFET consists of hole electron immobile charges none of the above

b

The drain characteristics of JFET in operating region, are inclined upwards almost flat inclined downwards inclined upwards or downwards

a

The intrinsic carrier concentration of silicon sample at 300 K is 1.5 x 1016/m3. If after doping, the number of majority carriers is 5 x 1020/m3. The minority carrier density is 4.5 x 1011/m3 3.33 x 104/m3 5 x 1020/m3 3 x 10-5/m3

c

The mean free path of conduction electrons in copper is about 4 x 10-8 m. For a copper block, find the electric field which can give, on an average, 1 eV energy to a conduction electron 2.62 x 107 V/m 2.64 x 107 V/m 2.5 x 107 V/m 2.58 x 107 V/m

b

The reverse saturation current of a diode does not depend on temperature. True False

b

The static characteristic of an adequately forward biased P-n junction is a straight line, if the plot is of __________ Vs → versus log I Vs log V log I Vs V I Vs log V I Vs V

b

The threshold voltage of an n-channel enhancement mode MOSFET is 0.5 when the device is biased at a gate voltage of 3V. Pinch off would occur at a drain voltage of 1.5 V 2.5 V 3.5 V 4.5 V

d

The units for transconductance are ohms amperes volts siemens

b

The value of a in a transistor is always equal to 1 is less than 1 but more than 0.9 is about 0.4 is about 0.1

b

The voltage across a zener diode is constant in forward direction is constant in reverse direction is constant in both forward and reverse directions none of the above

b

Two identical silicon diodes D1 and D2 are connected back to back shown in figure. The reverse saturation current Is of each diode is 10-8 amps and the breakdown voltage VBr is 50 v. Evaluate the voltages VD1 and VD2 dropped across the diodes D1 and D2 assuming KT/q to be 25 m V. 4.983 V, 0.017 V - 4.98 V, - 0.017 V 0.17 V, 4.983 V - 0.017 V, - 4.98 V

d

What is the correct sequence of the following step in the fabrication of a monolithic, Bipolar junction transistor?Emitter diffusion Base diffusion Buried layer formation E pi-layer formation Select the correct answer using the codes given below: 3, 4, 1, 2 4, 3, 1, 2 3, 4, 2, 1 4, 3, 2, 1

b

When a p-n junction is forward biased the width of depletion layer increases the width of depletion layer decreases the majority carriers move away from the junction the current is very small

a

When a p-n-p transistor is properly biased to operate in active region the holes from emitter. diffuse through base into collector region recombine with electrons in base recombine with electrons in emitter none of the above

b

When a reverse bias is applied to a p-n junction, the width of depletion layer. decreases increases remains the same may increase or decrease

d

Which of the following devices has a silicon dioxide layer? NPN transistor Tunnel diode JFET MOSFET

a

Which of the following has highest conductivity? Silver Aluminium Tungsten Platinum

d

Which of the following is used for generating time varying wave forms? MOSFET PIN diode Tunnel diode UJT

c

Which of these has degenerate p and n materials? Zener diode PIN diode Tunnel diode Photo diode

b

Which of these has highly doped p and n region? PIN diode Tunnel diode Schottky diode Photodiode

a

Which statement is false as regards holes Holes exist in conductors as well as semiconductors Holes constitute positive charges Holes exist only in semiconductors Holes and electrons recombine

c

n-type semiconductors are negatively charged are produced when indium is added as impurity to germanium are produced when phosphorus is added as impurity to silicon none of the above