Physics Part Ii Chapter 14 Semiconductor Electronics: Materials, Devices And Simple Circuits

A student wants to use two p-n junction diodes to convert alternating current into direct current. Draw the labelled circuit diagram she would use and explain how it works.

Give the truth table and circuit symbol for NAND gate.

Draw the typical input and output characteristics of an n-p-n transistor in CE configuration. Show how these characteristics can be used to determine (a) the input resistance (r_i), and (b) current amplification factor.

A p–n junction (D) shown in the figure can act as a rectifier. An alternating current source (V) is connected in the circuit.

The logic circuit shown below has the input waveforms ‘A’ and ‘B’ as shown. Pick out the correct output waveform.


output is

A working transistor with its three legs marked P, Q and R are tested using a multimeter. No conduction is found between P and Q. By connecting the common (negative) terminal of the multimeter to R and the other (positive) terminal of P or Q, some resistance is seen on the multimeter. Which of the following is true for the transistor?

• It is an n-p-n transistor with R as base

• It is a p-n-p transistor with R as collector

• It is a p-n-p transistor with R as emitter 

• It is an n-p-n transistor with R as collector

In the circuit below, A and B represent two inputs and C represents the output. The circuit represents

• NOR gate

• AND gate

• NAND gate

• OR gate

If in a p-n junction diode, a square input signal of 10V is applied as shown Then the output signal across RL will be 

For the given uniform square lamina ABCD, whose centre is O,

• 

• I_AD = 3I_EF

• I_AC = I_EF

• 

Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

• The number of free conduction electrons is significant in C but small in Si and Ge

• The number of free conduction electrons is negligibly small in all the three

• The number of free electrons for conduction is significant in all the three

• The number of free electrons for conduction is significant only in Si and Ge but small in C.

A thermocouple is made from two metals, Antimony and Bismuth. If one junction of the couple is kept hot and the other is kept cold then, an electric current will

• flow from Antimony to Bismuth at the cold junction

• flow from Antimony to Bismuth at the hot junction

• flow from Bismuth to Antimony at the cold junction

• not flow through the thermocouple

A solid which is transparent to visible light and whose conductivity increases with temperature is formed by

• Metallic binding

• Ionic binding

• Covalent binding

• Van der Waals binding

If the ratio of the concentration of electrons that of holes in a semiconductor is 7 /5 and the ratio of currents is 7/4, then what is the ratio of their drift velocities?

• 4/7

• 5/8

• 4/5

• 5/4

In a common base mode of a transistor, t collector current is 5.488 mA for an emit current of 5.60 mA. The value of the base current amplification factor (β) will be

• 48

• 49

• 50

• 51

The anode voltage of a photocell is kept fixed. The wavelength λ of the light falling on the cathode is gradually changed. The plate current I of the photocell varies as follows

If the lattice constant of this semiconductor is decreased, then which of the following is correct?

• All E_c, E_g, E_v decrease

• All E_c, E_g, E_v increase

• E_c, and E_v increase but E_g decreases

• E_c, and E_v, decrease E_g increases

In the following, which one of the diodes is reverse biased?

The circuit has two oppositely connect ideal diodes in parallel. What is the current following in the circuit?

• 1.33 A

• 1.71 A

• 2.00 A

• 2.31 A

The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The band gap in (eV) for the semiconductor is

• 1.1 eV

• 2.5 eV

• 0.5 eV

• 0.7 eV

In a common base amplifier, the phase difference between the input signal voltage and output voltage is

• π/4 

• π

• 0

• π/2

The thermistors are usually made of

• metals with low temperature coefficient of resistivity

• metals with high temperature coefficient of resistivity

• metal oxides with high temperature coefficient of resistivity ‘

• semiconducting materials having low temperature coefficient of resistivity.

When npn transistor is used as amplifier

• electrons move from base to collector

• holes move from emitter to base

• electrons move from collector to base

• holes move from base to emitter.

For a transistor amplifier in common emitter configuration having load impedance of 1 kΩ (h_fe = 50 and h_oe = 25) the current gain is

• -5.2

• -15.7

• -24.8

• -48.78

A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of

• each of them increases

• each of them decreases

• copper decreases and germanium increases

• copper increases and germanium decreases.

The manifestation of band structure in solids is due to

• Heisenberg’s uncertainty principle

• Pauli’s exclusion principle

• Bohr’s correspondence principle

• Boltzmann’s law

When p-n junction diode is forward biased

• the depletion region is reduced and barrier height is increased

• the depletion region is widened and barrier height is reduced.

• both the depletion region and barrier height reducedboth the depletion region and barrier height reduced

• both the depletion region and barrier height increased.

In a common emitter transistor amplifier, the audio signal voltage across the collector is 3 V. The resistance of collector is 3 kΩ. If current gain is 100 and the base resistance is 2 kΩ, the voltage and power gain of the amplifier is

• 200 and 1000

• 15 and 200

• 150 and 15000

• 20 and 2000

Which one of the following represents forward bias diode?

The given electrical network is equivalent to

• AND gate

• NOR gate

• OR gate

• NOT gate

In the combination of the following gates the output Y can be written in terms of inputs A and B as

• $\overline{A.B}$

• $A.\overline{B} + \overline{A}.B$

• $\overline{A +B}$

• $\overline{A.B} + A.B$

In the circuit shown in the figure, the input voltage V_i is 20 V, V_BE = 0 and V_CE = 0. The values of I_B, I_C and β are given by

• I_B = 40 μA, I_C = 10 mA, β = 250

• I_B = 25 μA, I_C = 5 mA, β = 200

• I_B = 40 μA, I_C = 5 mA, β = 125

• I_B = 20 μA, I_C = 5 mA, β = 250

In a p-n junction diode, change in temperature due to heating

• Affects only reverse resistance

• Affects only forward resistance

• Affects the overall V - I characteristics of p-n junction

• Does not affect resistance of p-n junction

The following circuit represents

• OR gate

• XOR gate

• AND gate

• NAND gate

The amplification factor of a triode valve is 15. If the grid voltage is changed by 0.3 V, the change in plate voltage in order to keep the current constant (in volt) is :

• 0.02

• 0.002

• 4.5

• 5.0

Zener diode is used for

• producing oscillations in an oscillator

• amplification

• stabilisation

• rectification

Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by _{${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} , {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}} \mathrm{and} {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$} respectively. Which one of the following relationships is true in their case?

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} > {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{si}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} = {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} < {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$

• ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}} > {\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

Choose the only false statement from the following

• Substances with energy gap ofthe order of 10 eV are insulators 

• The conductivity of a semiconductor increases with  increases in temperature

• In conductors the valence and conduction bands may overlap

• The resistivity of a semiconductor increases with increase in temperature

The total energy of an electron in the first excited state of hydrogen is about -3.4 eV. Its kinetic energy in this state is

• -3.4 eV

• -6.8 eV

• 6.8 eV

• 3.4 eV

Which logic gate is represented by the following combination of logic gates?

• OR

• NOR

• AND

• NAND

The principle of LASER action involves

• amplification of particular frequency emitted by the system

• population inversion

• stimulated emission

• All of the above

Which of the following is unipolar transistor?

• p-n-p transistor

• n-p-n transistor

• Field effect transistor

• Point contact transistor

The truth table given below is for (A and B are the inputs, Y is the output)

• NOR

• AND

• XOR

• NAND

Which logic gate is represented by the following combination of logic gates?

• OR

• NOR

• AND

• NAND

The reason of current flow in p-n junction in forward bias is

• drifting of charge carriers

• drifting of minority charge carriers

• diffussion of charge carriers

• All of the above

A change of 8.0 mA in the emitter current brings a change of 7. 9 mA in the collector current. The value of a will be

• 0.96

• 0.93

• 0.90

• 0.99

The truth table for the following logic circuit is

• $\left|\begin{array}{ccc}\mathrm{A}& \mathrm{B}& \mathrm{Y}\\ 0& 0& 0\\ 0& 1& 1\\ 1& 0& 1\\ 1& 1& 0\end{array}\right|$

• $\left|\begin{array}{ccc}\mathrm{A}& \mathrm{B}& \mathrm{Y}\\ 0& 0& 1\\ 0& 1& 1\\ 1& 0& 1\\ 1& 1& 1\end{array}\right|$

• $\left|\begin{array}{ccc}\mathrm{A}& \mathrm{B}& \mathrm{Y}\\ 0& 0& 1\\ 0& 1& 0\\ 1& 0& 1\\ 1& 1& 0\end{array}\right|$

• $\left|\begin{array}{ccc}\mathrm{A}& \mathrm{B}& \mathrm{Y}\\ 0& 0& 1\\ 0& 1& 1\\ 1& 0& 0\\ 1& 1& 1\end{array}\right|$

The transfer ratio B of a transistor is 50. The input resistance of the transistor when used in the common emitter configuration is 2 kΩ. The peak value of the collector AC current for an AC input voltage of 0.02 V peak is

• 200 μA

• 0.01 mA

• 0.25 mA

• 500 μA

In the circuit shown in figure, when the input voltage of the base resistance is 10 V, Vb, is zero and V_ce is also zero. Value of β is

• 133

• 154

• 196

• 105

Assertion: An n-type semiconductor has a large number of electrons but still it is electrically neutral.

Reason: An n-type semiconductor is obtained by doping an intrinsic semiconductor with a pentavalent impurity.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

A transistor connected at common emitter mode contains load resistance of 5 kΩ and an input resistance of 1 kΩ. If the input peak voltage is 5 mV and the current gain is 50, find the voltage gain.

• 250

• 500

• 125

• 50

The output for the given, circuit is

• $\left( \mathrm{A} + \mathrm{B} \right)$$·$ $\overline{\mathrm{B}}$

• (A $·$ B) $·$ B

• ( A + B )$·$B

• ( A $·$ B ) + B

If the plate resistance oftriode valve is 13 x 10⁶ Ω and amplification factor is 21. The mutual conductance will be

• 1.6 × 10^-6 mho

• 1.6 × 10⁶ mho

• 2.6 × 10^-5 mho

• 2.6 × 10⁵ mho

Assertion:  A p-n junction with reverse bias can be used as a photo-diode to measure light intensity. 

Reason:  In a reverse bias condition the current is small but it is more sensitive to change in intensity of incident light.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  The output voltage and the input voltage of the NOT gate have 180° phase difference. 

Reason:  The logic NOT can be built using diode.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  In a common emitter transistor amplifier, the input current is much less than the output current than output impedance. 

Reason: The common emitter transistor amplifier has higher input impedance than output impedance.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.