An electromagnetic wave passes from vacuum into a dielectric medium with relative electrical permittivity $(3/2)$ and relative magnetic permeability $(8/3)$. Then, its
(A) wavelength is doubled and frequency remains unchanged.
(B) wavelength is doubled and frequency is halved.
(C) wavelength is halv...
CBSE CLASS 12 • PHYSICS • CHAPTER 14
Semiconductor Electronics: Materials, Devices and Simple Circuits
180 distinct questions across 295 board paper set appearances (2022–2026).
In an unbiased p-n junction, at equilibrium, which of the following statements is true ?
(A) Diffusion current is zero but drift current exists.
(B) Diffusion current exists but drift current is zero.
(C) Diffusion and drift currents are equal and opposite.
(D) Both the diffusion and drift currents ...
(III) If the intensity of the incident radiation for both metals A and B, is doubled keeping its frequency constant, then
(A) the slope of the parallel lines will increase.
(B) the slope of the parallel lines will decrease.
(C) the threshold frequencies for both A and B will decrease.
(D) the slope...
Write two points of difference between intrinsic and extrinsic semiconductors.
A p-type or n-type semiconductor can be converted into a p-n junction by doping it with suitable impurity. The motion of majority charge carriers causes diffusion current across the junction while the barrier electric field causes motion of minority carriers for drift current. In case of unbiased di...
With the help of circuit diagrams, briefly explain the forward biasing and the reverse biasing of a p-n junction diode.
In a reversed-biased p-n junction diode, the applied voltage mostly drops across :
(A) p-region only
(B) n-region only
(C) depletion region
(D) the diode
Assertion (A): The conductivity of an n-type semiconductor is higher than that of a p-type semiconductor at a given temperature. Reason (R): The electrons being in the conduction band in n-type semiconductor are more mobile than the holes in the valence band in p-type semiconductor.
The hole concentration in an intrinsic semiconductor is $5 \times 10^8 \text{ m}^{-3}$. When it is doped with certain impurity, the electron concentration becomes $4 \times 10^{12} \text{ m}^{-3}$. Find the new value of the hole concentration. Also identify the type of new semiconductor formed after...
A good diode checked by a multimeter should indicate :
(A) high resistance in reverse bias and a low resistance in forward bias
(B) high resistance in both forward bias and reverse bias
(C) low resistance in both reverse bias and forward bias
(D) high resistance in forward bias and low resistance in...
In forward and reverse biased silicon p-n junction, the dominant mechanisms for the motion of charge carriers are :
(A) diffusion in forward bias, drift in reverse bias
(B) drift in both forward bias and in reverse bias
(C) drift in forward and diffusion in reverse bias
(D) diffusion in both forward...
Draw a labelled diagram of a full wave rectifier circuit. State its working principle and show the input-output waveforms.
Assertion (A) : n-type semiconductor is not negatively charged.
Reason (R) : Neutral pentavalent impurity atom doped in intrinsic semiconductor (neutral) donates its fifth unpaired electron to the crystal lattice and becomes a positive donor.
In an intrinsic semiconductor, carrier's concentration is $5 \times 10^8 \text{ m}^{-3}$. On doping with impurity atoms, the hole concentration becomes $8 \times 10^{12} \text{ m}^{-3}$.
(a) Identify (i) the type of dopant and (ii) the extrinsic semiconductor so formed.
(b) Calculate the electron co...
(a) What are majority and minority charge carriers of p-type and n-type semiconductors ?
(b) Explain briefly the formation of diffusion current and drift current in a p-n junction diode.
Assertion (A) : In Rutherford's alpha particle scattering experiment, the presence of only few alpha particles at angle of scattering $\pi$ led him to the discovery of nucleus.
Reason (R) : The size of nucleus is approximately $10^{-5}$ times the size of an atom and therefore only few alpha particle...
Differentiate between half-wave and full-wave rectification. With the help of a circuit diagram, explain the working of a full-wave rectifier.
In an n-type semiconductor electron-hole combination is a continuous process at room temperature. Yet the electron concentration is always greater than the hole concentration in it. Explain.
A p-n junction diode is forward biased. As a result,
(A) both the potential barrier height and the width of depletion layer decrease.
(B) both the potential barrier height and the width of depletion layer increase.
(C) the potential barrier height decreases and the width of depletion layer increases...
Draw energy band diagrams of n-type and p-type semiconductors at temperature $T > 0\text{ K}$. Show the donor/acceptor energy levels with the order of difference of their energies from the bands.
Explain the process of formation of 'depletion layer' and 'potential barrier' in a p-n junction region of a diode, with the help of a suitable diagram. Which feature of junction diode makes it suitable for its use as a rectifier ?
Assertion (A) : The electrical conductivity of a pure Ge crystal increases with increase in its temperature.
Reason (R) : The number of electrons excited by thermal excitation from the valence band to the conduction band, in a semiconductor, increases with increase in temperature.
With the help of a circuit diagram, describe the method to obtain p-n junction diode characteristic when it is forward biased. Draw the shape of the characteristic.
According to the band theory of solids, a semiconductor has a valence band and a conduction band separated by a gap, known as energy band gap. Pure semiconductors are called intrinsic semiconductors. At room temperature, some electrons from the valence band can acquire enough energy to cross the ban...
In a p-n junction diode under reverse bias, the barrier height :
(A) is reduced and the depletion layer width decreases.
(B) is reduced and the depletion layer width increases.
(C) increases and the depletion layer width also increases.
(D) increases and the depletion layer width decreases.
Ge is doped with As. Due to doping,
(A) the structure of Ge lattice is distorted.
(B) the number of conduction electrons increases.
(C) the number of holes increases.
(D) the number of conduction electrons decreases.
When a p-n junction diode is forward biased
(A) the barrier height and the depletion layer width both increase.
(B) the barrier height increases and the depletion layer width decreases.
(C) the barrier height and the depletion layer width both decrease.
(D) the barrier height decreases and the deple...
(a) Draw circuit arrangement for studying V-I characteristics of a p-n junction diode.
(b) Show the shape of the characteristics of a diode.
(c) Mention two information that you can get from these characteristics.
(a) What are majority and minority charge carriers in an extrinsic semiconductor ?
(b) A p-n junction is forward biased. Describe the movement of the charge carriers which produce current in it.
(c) The graph shows the variation of current with voltage for a p-n junction diode.
[Graph showing I (mA)...
An n-type semiconducting Si is obtained by doping intrinsic Si with :
(A) Al
(B) B
(C) P
(D) In
When a p-n junction diode is subjected to reverse biasing :
(A) the barrier height decreases and the depletion region widens.
(B) the barrier height increases and the depletion region widens.
(C) the barrier height decreases and the depletion region shrinks.
(D) the barrier height increases and the ...
How does the energy gap of an intrinsic semiconductor effectively change when doped with a (a) trivalent impurity, and (b) pentavalent impurity ? Justify your answer in each case.
With the help of a circuit diagram, explain the working of a p-n junction diode as a full wave rectifier. Draw its input and output waveforms.
The output in a half-wave rectifier is :
(A) unidirectional without ripple
(B) steady and continuous
(C) unidirectional with ripple
(D) steady but discontinuous
In a p-n junction diode, the majority charge carriers on p-side and on n-side are, respectively :
(A) electrons, electrons
(B) electrons, holes
(C) holes, holes
(D) holes, electrons
Assertion (A): In a semiconductor, the electrons in the conduction band have lesser energy than those in the valence band.
Reason (R): Donor energy level is just above the valence band in a semiconductor.
The number of peaks of the interference formed if the slit width is doubled while keeping the distance between the slits same will be: (A) 1 (B) 2 (C) 3 (D) 4
Assertion (A) : The temperature coefficient of resistance is positive for metals and negative for p-type semiconductors.
Reason (R) : The charge carriers in metals are negatively charged, whereas the majority charge carriers in p-type semiconductors are positively charged.
Draw the circuit diagram of a p-n junction diode in (i) forward biasing and (ii) reverse biasing. Also draw its I-V characteristics in the two cases.
A pure semiconductor like Ge or Si, when doped with a small amount of suitable impurity, becomes an extrinsic semiconductor. In thermal equilibrium, the electron and hole concentration in it are related to the concentration of intrinsic charge carriers. A p-type or n-type semiconductor can be conver...
(a) Explain the characteristics of a p-n junction diode that makes it suitable for its use as a rectifier.
(b) With the help of a circuit diagram, explain the working of a full wave rectifier.
Explain the following, giving reasons :
(a) A doped semiconductor is electrically neutral.
(b) In a p-n junction under equilibrium, there is no net current.
(c) In a diode, the reverse current is practically not dependent on the applied voltage.
Assertion (A) : Silicon is preferred over germanium for making semiconductor devices.
Reason (R) : The energy gap for germanium is more than the energy gap for silicon.
(a) (i) Draw the circuit diagram used to study $I - V$ characteristics of a p-n junction diode in conducting mode. Mark on the graph the threshold voltage of the diode. Explain the significance of this voltage.
(ii) In the circuit shown in the figure, the forward voltage drop across the diode is $0\...
Draw energy band diagrams of n-type and p-type semiconductors at temperature $T > 0\text{K}$, depicting the donor and acceptor energy levels. Mention the significance of these levels.
State the working principle of an LED. Write any two important advantages and two disadvantages of LED.
Explain the formation of depletion region in a p-n junction.
With the help of a circuit diagram, explain the working of a p-n junction diode as a full-wave rectifier. Also draw its input and output waveforms.
Assertion (A) : On forward biasing a p-n junction diode, the height of the barrier potential increases.
Reason (R) : In forward biasing of a p-n junction diode, the direction of the applied voltage is in the same direction as the built-in potential.
When the forward bias voltage in a semiconductor diode is changed from $0\cdot8\text{ V}$ to $1\cdot0\text{ V}$, the forward current changes by $2\cdot0\text{ mA}$. The forward bias resistance of the diode will be :
(A) $200\text{ }\Omega$
(B) $175\text{ }\Omega$
(C) $100\text{ }\Omega$
(D) $125\tex...
Draw a circuit diagram of a full-wave rectifier using p-n junction diodes. Explain its working and show the input-output waveforms.
Assertion ($A$) : The impurities in p-type Si are not pentavalent atoms.
Reason ($R$) : The hole density in valance band in p-type semiconductor is almost equal to the acceptor density.
Assertion (A) : A hole is an apparent free particle with effective positive electronic charge.
Reason (R) : A hole is not necessarily a vacancy left behind by an electron in the valence band.
(iii) During formation of a p-n junction :
(A) a layer of negative charge on n-side and a layer of positive charge on p-side appear.
(B) a layer of positive charge on n-side and a layer of negative charge on p-side appear.
(C) the electrons on p-side of the junction move to n-side initially.
(D) ini...
(iv) (a) In reverse-biased p-n junction :
(A) the drift current is of the order of few $\text{mA}$.
(B) the applied voltage mostly drops across the depletion region.
(C) the depletion region width decreases.
(D) the current increases with increase in applied voltage.
OR
(b) The output frequency of a...
Extrinsic semiconductors are made by doping pure or intrinsic semiconductors with suitable impurity. There are two type of dopants used in doping, Si or Ge, and using them p-type and n-type semiconductors can be obtained. A p-n junction is the basic building block of many semiconductor devices. Two ...
Assertion (A) : We cannot form a p-n junction diode by taking a slab of a p-type semiconductor and physically joining it to another slab of a n-type semiconductor. Reason (R) : In a p-type semiconductor $n_e >> n_h$ while in a n-type semiconductor $n_h >> n_e$.
A p-type Si semiconductor is made by doping an average of one dopant atom per $5 \times 10^7$ silicon atoms. If the number density of silicon atoms in the specimen is $5 \times 10^{28}$ atoms $\text{m}^{-3}$, find the number of holes created per cubic centimetre in the specimen due to doping. Also g...
When the resistance measured between p and n ends of a p-n junction diode is high, it can act as a/an -
(A) resistor
(B) inductor
(C) capacitor
(D) switch
The root mean square value of an alternating voltage applied to a full-wave rectifier is $\frac{V_0}{\sqrt{2}}$. Then the root mean square value of the rectified output voltage is :
(A) $\frac{V_0}{\sqrt{2}}$
(B) $\frac{V_0^2}{\sqrt{2}}$
(C) $\frac{2V_0}{\sqrt{2}}$
(D) $\frac{V_0}{2\sqrt{2}}$
In a full-wave rectifier, the current in each of the diodes flows for :
(A) Complete cycle of the input signal
(B) Half cycle of the input signal
(C) Less than half cycle of the input signal
(D) Only for the positive half cycle of the input signal
In a full-wave rectifier :
(A) Both diodes are forward biased at the same time.
(B) Both diodes are reverse biased at the same time.
(C) One is forward biased and the other is reverse biased at the same time.
(D) Both are forward biased in the first half of the cycle and reverse biased in the second...
If the frequency of the half-wave rectifier is $50 \text{ Hz}$, the frequency of full-wave rectifier is :
(A) $25 \text{ Hz}$
(B) $50 \text{ Hz}$
(C) $100 \text{ Hz}$
(D) $200 \text{ Hz}$
(ii) (a) A full-wave rectifier circuit is shown in the figure. The contribution in output waveform from junction diode D_1 is: (A) A, D (B) A, C (C) B, D (D) B, C
(a) Draw the circuit diagrams for obtaining the $\text{V} - \text{I}$ characteristics of a p-n junction diode. Explain briefly the salient features of the $\text{V} - \text{I}$ characteristics in (i) forward biasing, and (ii) reverse biasing.
OR
(b) On the basis of energy band diagrams, distinguish ...
Define the term - Distance of closest approach. How will it be affected, for an $\alpha$ - particle, if kinetic energy of the particle is doubled ?
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct ex...
Briefly explain the two important processes that occur during the formation of a p-n junction.
A semiconductor has equal electron and hole concentration of $3 \times 10^8\text{ m}^{-3}$. On doping with a certain impurity, the hole concentration increases to $6 \times 10^{10}\text{ m}^{-3}$.
(a) What type of semiconductor is obtained on doping ?
(b) Calculate the new electron concentration of ...
(a) Draw the V-I characteristics of silicon diode.
(b) Explain the following terms :
(i) minority carrier injection in forward bias
(ii) breakdown voltage in reverse bias
Assertion (A) : On forward biasing a p-n junction diode, the height of the barrier potential increases.\nReason (R) : In forward biasing of a p-n junction diode, the direction of the applied voltage is in the same direction as the built-in potential.
(iii) During forward biasing of a p-n junction diode, the
(A) current is mainly due to drifting of majority carriers.
(B) current is mainly due to drifting of minority carriers.
(C) diffusion and drift currents are equal.
(D) current is of the order of $1\text{ A}$.
Two identical circular loops A and B of metal wire are arranged on a table close to each other. Loop A is connected to a battery and the current in it increases with time. In response, the loop B
(A) remains stationary
(B) is attracted by loop A
(C) is repelled by loop A
(D) rotates about its centre...
Which of the following element can be used as dopant in Si crystal to obtain a p-type semiconductor ?
(A) Phosphorus
(B) Arsenic
(C) Boron
(D) Antimony
Write two points of difference between intrinsic semiconductors and extrinsic semiconductors.
Explain the working of a full-wave rectifier. Differentiate between a half-wave rectifier and a full-wave rectifier.
A n-type semiconductor is obtained by doping silicon with (A) Boron (B) Arsenic (C) Indium (D) Aluminium
When a forward biasing is applied across a junction diode, it – (A) raises the potential barrier height. (B) decreases the depletion layer width. (C) increases the resistance of the p-n junction. (D) reduces the majority carrier current to zero.
Differentiate between n-type and p-type semiconductors.
(a) Explain the working of a junction diode as a half-wave rectifier. (b) The efficiency of a half-wave rectifier is $40%$. What happens to the remaining $60%$ power ?
The process named 'minority carrier injection' in a p-n junction diode occurs during :
(A) forward biasing
(B) reverse biasing
(C) no biasing at low temperature
(D) no biasing at high temperature
How are charge carriers created in an intrinsic semiconductor ? Explain.
Which of the following p-n junction diodes is forward biased ?
(A) $+ 5\text{ V}$ terminal connected to p-side, $+ 10\text{ V}$ terminal connected to n-side
(B) $- 1\cdot0\text{ V}$ terminal connected to p-side, $- 1\cdot5\text{ V}$ terminal connected to n-side
(C) $0\text{ V}$ terminal connected to...
Explain, with the help of suitable diagram, the two important processes that occur during the formation of a p-n junction.
When the forward bias voltage in a semiconductor diode is changed from $0.8 \text{ V}$ to $1.0 \text{ V}$, the forward current changes by $2.0 \text{ mA}$. The forward bias resistance of the diode will be : (A) $200 \; \Omega$ (B) $175 \; \Omega$ (C) $100 \; \Omega$ (D) $125 \; \Omega$
If the given figure, $V_0$ is the potential barrier across a p-n junction in an unbiased condition. Which of the following statements is correct ?
(A) Curves 1 and 3 both correspond to forward biasing of p-n junction.
(B) Curve 3 corresponds to forward biasing and Curve 1 corresponds to reverse bias...
Write any two points of difference between intrinsic and extrinsic semiconductors.
A tank is filled with a liquid to a height of $12\cdot5$ m. The apparent depth of a needle lying at the bottom of the tank is measured to be $9\cdot0$ m. Calculate the speed of light in the liquid.
A ray of light MN is incident normally on the face corresponding with side AB of a prism with an isosceles right-angled triangular base ABC. Trace the path of the ray as it passes through the prism when the refractive index of the prism material is (i) $\sqrt{2}$ , and (ii) $\sqrt{3}$ .
The frequency of the incident light on a metal surface is doubled. Find the new value of the maximum kinetic energy of the electrons and comment on its magnitude in comparison to the initial maximum kinetic energy of electrons.
When the distance between the slit and screen is doubled, the angular separation between two fringes in single-slit diffraction experiment will :
(A) be doubled
(B) be halved
(C) remain constant
(D) become one-fourth
When an external voltage is applied across a semiconductor diode such that p-side is connected to the positive terminal of the battery and n-side to the negative terminal it is said to be forward biased. The applied voltage mostly drops across the depletion region and the voltage drop across the p-s...
(I) $ ext{Ge}$ and $ ext{Si}$ diodes start conducting at $0.3 ext{ V}$ and $0.7 ext{ V}$ respectively. In the following figure if $ ext{Ge}$ diode connection are reversed, the value of $V_0$ changes by (assume that the $ ext{Ge}$ diode has large breakdown voltage)
(A) $0.2 ext{ V}$
(B) $0.4 ext{ V...
(III) Plot a graph showing this variation in reading of micrometre on shifting the terminal B towards the right.
(for V.I. candidates)
(III) If the intensity of incident radiation is doubled, by what factor will the kinetic energy change?
Which of the following impurity atoms, when doped in silicon, would produce an n-type semiconductor ?
(A) Arsenic
(B) Aluminium
(C) Boron
(D) Indium
Which of the following statements is correct during formation of a p-n junction ?
(A) Initially the diffusion current is small and the drift current is large.
(B) Initially the diffusion current and the drift current are equal to each other.
(C) Finally, the diffusion current and the drift current a...
In a p-type $\text{Si}$ semiconductor sample the hole concentration is $2\cdot25\times 10^{15}\text{ cm}^{-3}$. If the intrinsic carrier concentration is $1\cdot5\times 10^{10}\text{ cm}^{-3}$, calculate the electron concentration in the sample.
(a) Differentiate between the two types of extrinsic semiconductors.
(b) The mobility of an electron in the conduction band of a semiconductor is more than the mobility of a hole (or electron) in the valance band. Explain why.
A monochromatic laser beam is incident perpendicularly to the wall of a water-filled glass container. The laser beam passes through two slits in a block kept in the container. An interference pattern is formed on a screen inside the container. The water is then replaced with a transparent fluid of g...
(iii) (a) In the above experiment (with water), if the separation between the slits is halved and distance between the slits and the screen in doubled, the fringe width is :
(A) doubled
(B) quadrupled
(C) halved
(D) unchanged
Questions number 13 to 16 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
(A) Both Assertion (A) and Reason (R) are true and Reason...
Assertion (A) : The impurities in p-type $\text{Si}$ are not pentavalent atoms.
Reason (R) : The hole density in valance band in p-type semiconductor is almost equal to the acceptor density.
As the current ($I_g$) which produces full scale deflection in the galvanometer is very small, the galvanometer cannot as such be used to measure current in electric circuits. A small resistance, called shunt, of a suitable value is connected with the galvanometer to convert it into an ammeter of de...
As the current ($I_{\text{g}}$) which produces full scale deflection in the galvanometer is very small, the galvanometer cannot as such be used to measure current in electric circuits. A small resistance, called shunt, of a suitable value is connected with the galvanometer to convert it into an amme...
A right-angled prism $\text{ABC}$ (refractive index $\sqrt{2}$) is kept on a plane mirror as shown in the figure. A ray of light is incident normally on the face $\text{AC}$.
(a) Trace the path of the ray as it passes through the prism.
(b) Find the angle of deviation produced by the prism.
A right angled isosceles glass prism ABC is kept in contact with an equilateral triangular prism DBC as shown in the figure. Both prisms are made of the same glass of refractive index $1\cdot6$. Trace the path of the ray MN incident normally on face AB as it passes through the combination.
Assertion (A) : A hole is an apparent free particle with effective positive electronic charge.\nReason (R) : A hole is not necessarily a vacancy left behind by an electron in the valence band.
A tank is filled with a liquid of refractive index $\sqrt{2}$, up to a height of $30\text{ cm}$. A tiny bulb is glowing at the bottom of the tank. Calculate the diameter of an opaque disc floating symmetrically on the liquid surface that can cut off completely the light from the bulb that comes out ...
(ii) The impurity atoms with which pure $ ext{Ge}$ should be doped to convert it into an n-type semiconductor, is :
(A) Boron
(B) Phosphorous
(C) Aluminium
(D) Indium
Two long, straight, parallel conductors carry the same current and attract each other with a force $F$ per unit length. If the current is doubled in each conductor and their separation is made half, the force per unit length becomes :
(A) $\frac{F}{2}$
(B) $2F$
(C) $4F$
(D) $8F$
(b) In a unbiased p-n junction :
(A) the diffusion current is zero everywhere.
(B) the drift current is zero everywhere.
(C) the electric potential is zero everywhere.
(D) the drift current and the diffusion current cancel each other.
(ii) The impurity atoms with which pure Ge should be doped to convert it into an n-type semiconductor, is :
(A) Boron
(B) Phosphorous
(C) Aluminium
(D) Indium
A beaker is filled with water (refractive index $\frac{4}{3}$) upto a height H. A coin is placed at its bottom. The depth of the coin, when viewed along the near normal direction, will be
(A) $\frac{\text{H}}{4}$
(B) $\frac{3\text{H}}{4}$
(C) H
(D) $\frac{4\text{H}}{3}$
Assertion (A) : We cannot form a p-n junction diode by taking a slab of a p-type semiconductor and physically joining it to another slab of an n-type semiconductor.
Reason (R) : In a p-type semiconductor $n_e \gg n_h$ while in an n-type semiconductor $n_h \gg n_e$.
A p-type Si semiconductor is made by doping an average of one dopant atom per 5 × 10⁷ silicon atoms. If the number density of silicon atoms in the specimen is 5 × 10²⁸ atoms m⁻³, find the number of holes created per cubic centimetre in the specimen due to doping. Also give one example of such dopant...
A tub is filled with a transparent liquid to a height of 30.0 cm. The apparent depth of a coin lying at the bottom of the tub is found to be 16.0 cm. The speed of light in the liquid will be (A) 1.6 × 10^8 m s^-1 (B) 2.0 × 10^8 m s^-1 (C) 3.0 × 10^8 m s^-1 (D) 2.5 × 10^8 m s^-1
When the resistance measured between $\text{p}$ and $\text{n}$ ends of a p-n junction diode is high, it can act as a/an -
(A) resistor
(B) inductor
(C) capacitor
(D) switch
A diamagnetic substance is brought, one by one, near the north pole and the south pole of a bar magnet. It is
(A) repelled by north pole and attracted by south pole.
(B) attracted by north pole and repelled by south pole.
(C) attracted by north pole as well as by south pole.
(D) repelled by north po...
Which of the following impurity atoms when doped in silicon, would produce a p-type semiconductor ?
(A) Phosphorus
(B) Arsenic
(C) Antimony
(D) Boron
When the voltage across a p-n junction diode is increased from $0.90\text{ V}$ to $0.95\text{ V}$, the diode current changes by $0.005\text{ A}$. Find the dynamic resistance of the diode.
How does the conductivity of an intrinsic semiconductor vary with temperature ? Explain. Show the variation in a plot.
(b) A signal, as shown in the figure, is applied to a p-n junction diode. Identify the output across resistance $R_L$ :
Differentiate between 'diffusion current' and 'drift current'. Explain their role in the formation of p-n junction.
An alternating voltage of frequency of $50\text{ Hz}$ is applied to a half-wave rectifier. Then the ripple frequency of the output will be : (A) $100\text{ Hz}$ (B) $50\text{ Hz}$ (C) $25\text{ Hz}$ (D) $150\text{ Hz}$
A signal, as shown in the figure, is applied to a p-n junction diode. Identify the output across resistance $R_L$ : [Figure showing an input signal with +5 V and -5 V levels and a circuit diagram with a diode and resistor $R_L$] (A) Graph starting at 10 V (B) Graph at -10 V (C) Graph at -5 V (D) Gra...
The number of electrons made available for conduction by dopant atoms depends strongly upon
(A) doping level
(B) increase in ambient temperature
(C) energy gap
(D) options (A) and (B) both
(for V.I. Candidates) Explain briefly how (i) barrier potential is formed in p-n junction diode. (ii) Width of depletion region of the diode is affected when it is (a) forward biased, (b) reverse biased.
Q25. (I) Draw the energy band diagram for P-type semiconductor at (i) T=0K and (ii) room temperature. (II) In the given diagram considering an ideal diode, in which condition will the bulb glow (a) when the switch is open (b) when the switch is closed. Justify your answer.
Q27. A light ray entering a right-angled prism undergoes refraction at the face AC as shown in Fig. 1. (I) What is the refractive index of the material of the prism in Fig. 1?
The element of a heater is cut into two equal parts. Now only one part is used in the heater. The heat generated now as compared to the original rating of the heater will be :
(A) halved
(B) doubled
(C) four times
(D) same
The majority and the minority charge carriers inside a p-type semiconductor are respectively :
(A) electrons, holes
(B) holes, electrons
(C) holes, holes
(D) electrons, electrons
The output of a full-wave rectifier is :
(A) steady
(B) continuous with ripple
(C) continuous without any ripple
(D) zero during alternate half cycles of input
Explain the formation of potential barrier across an unbiased p-n junction. Write the effect on height of the barrier when a p-n junction is (a) forward biased, and (b) reverse biased.
(a) Explain the formation of valence and conduction band in a crystal.
(b) Discuss the difference between energy bands of (i) a metal, (ii) an insulator, and (iii) a semiconductor.
Which of the following statements is \textit{not} true for a p-n junction diode under reverse bias ?
(A) The current is almost independent of the applied voltage.
(B) Holes flow from p-side to n-side.
(C) Electric field in the depletion region increases.
(D) n-side of the junction is connected to +v...
Two halves of a silicon crystal (A and B) are doped with arsenic and boron respectively, forming a p-n junction in it. A battery is connected across it as shown in the figure.
(a) Will the junction be forward biased or reverse biased ? Give reason.
(b) Draw V-I graph for this arrangement.
A full-wave rectifier circuit is shown in the figure. The contribution in output waveform from junction diode $D_1$ is :
(A) A, D
(B) A, C
(C) B, D
(D) B, C
Which of the following statements is not true for a p-n junction diode under reverse bias ?
(A) The current is almost independent of the applied voltage.
(B) Holes flow from p-side to n-side.
(C) Electric field in the depletion region increases.
(D) n-side of the junction is connected to +ve termina...
Name the impurity atoms which are doped in an intrinsic semiconductor to convert it into (a) p-type, and (b) n-type semiconductor. Draw energy band diagrams of p-type and n-type semiconductors at temperature $T > 0 \text{ K}$. Mark the donor and acceptor energy levels, showing the energy difference ...
When intrinsic silicon semiconductor is doped with Al atom, then it :
(A) decreases the number of holes in the conduction band.
(B) increases the number of holes in the valence band.
(C) increases the energy gap value.
(D) increases the number of electrons in the valence band.
Explain the terms depletion layer and potential barrier for a junction diode and their formation.
Suppose a pure Si crystal has $5 \times 10^{28} \text{ atoms m}^{-3}$. It is doped by 1 ppm concentration of boron. Calculate the concentration of holes and electrons, given that $n_i = 1.5 \times 10^{16} \text{ m}^{-3}$. Is the doped crystal n-type or p-type?
Suppose a pure Si crystal has $5 \times 10^{28}$ atoms $\text{m}^{-3}$. It is doped by 1 ppm concentration of boron. Calculate the concentration of holes and electrons, given that $\text{n}_i = 1.5 \times 10^{16} \text{m}^{-3}$. Is the doped crystal n-type or p-type ?
Suppose a pure $\text{Si}$ crystal has $5 \times 10^{28}\text{ atoms m}^{-3}$. It is doped by $1\text{ ppm}$ concentration of boron. Calculate the concentration of holes and electrons, given that $n_{\text{i}} = 1.5 \times 10^{16}\text{ m}^{-3}$. Is the doped crystal n-type or p-type ?
(a) Draw the circuit diagrams for obtaining the $V-I$ characteristics of a p-n junction diode. Explain briefly the salient features of the $V-I$ characteristics in (i) forward biasing, and (ii) reverse biasing.
OR
(b) On the basis of energy band diagrams, distinguish between (i) an insulator, (ii) a...
An ac voltage $V = 0.5 \sin $100 \pi t$$ volt is applied, in turn, across a half-wave rectifier and a full-wave rectifier. The frequency of the output voltage across them respectively will be
(A) $25 \text{ Hz}, 50 \text{ Hz}$
(B) $25 \text{ Hz}, 100 \text{ Hz}$
(C) $50 \text{ Hz}, 50 \text{ Hz}$
(D...
(i) When Ge is doped with pentavalent impurity, the energy required to free the weakly bound electron from the dopant is about
(A) 0.001 eV
(B) 0.01 eV
(C) 0.72 eV
(D) 1.1 eV
(ii) At a given temperature, the number of intrinsic charge carriers in a semiconductor is $2.0 \times 10^{10} \text{ cm}^{-3...
The effect on width of depletion layer and height of the potential barrier of a p-n junction, when it is forward biased, are respectively :
(A) decreases, decreases
(B) increases, increases
(C) decreases, increases
(D) increases, decreases
The doping of a semiconductor with donor impurity results in :
(A) formation of a p-type semiconductor
(B) formation of a new energy level just above the filled valence band
(C) decrease in the concentration of electrons
(D) formation of a new energy level just below the conduction band
Explain the formation of energy bands in solids and hence define conduction band and valence band.
A point source of light is kept at the bottom of a tank filled with a transparent liquid up to a height H. If the radius of the circular patch on the surface from which light can come out is $\frac{H}{\sqrt{3}}$, the refractive index of the liquid is close to :
(A) 1.3
(B) 1.5
(C) 1.7
(D) 2.0
In which of the following figures, the pn diode is reverse biased?
In an intrinsic semiconductor, the intrinsic carrier concentration ($n_i$), electron concentration ($n_e$) and hole concentration ($n_h$) are related as :
(a) $n_e + n_h = n_i$
(b) $n_i = \sqrt{n_e n_h}$
(c) $n_e = n_h = n_i$
(d) $n_e + n_h = \frac{n_i}{2}$
Define the following terms in relation to the working of a p-n junction diode :
(i) Knee voltage
(ii) Reverse saturation current
(a) How are the potential barrier and width of the depletion region affected when a p-n junction diode is (i) forward-biased, and (ii) reverse-biased ?
OR
(b) Briefly explain doping of a semiconductor and its necessity.
A small object lies at the bottom of a vessel filled with water (refractive index $4/3$) up to a height $H$. When viewed from a point above the surface of water, the object appears raised by $n$ percent of $H$. The value of $n$ is :
(a) 15
(b) 20
(c) 25
(d) 33
A small bar, when placed near a magnet is repelled by it. This is because the bar is made of :
(a) Iron
(b) Copper
(c) Aluminium
(d) Nickel
Which of the following dopants in silicon will make it a p-type semiconductor ?
(a) As
(b) Al
(c) Sb
(d) P
When a p-n junction diode is forward biased :
(a) the depletion layer width increases and the barrier height is reduced.
(b) the depletion layer width decreases and the barrier height is reduced.
(c) both the depletion layer width and the barrier height increase.
(d) the depletion layer width decrea...
Briefly explain how the valence band and conduction band are formed in a crystal.
Explain how a depletion region is formed in a p-n junction.
Write the characteristics of a p-n junction which make it suitable for rectification.
Explain the formation of depletion layer and barrier potential in a p-n junction diode.
Distinguish between intrinsic and extrinsic semiconductors. Although in an extrinsic semiconductor $n_e \neq n_h$, yet it is electrically neutral. Why ?
How is an emf generated by a solar cell due to the three basic processes involved ? Explain.
Briefly explain the working of a light emitting diode. Mention its two uses.
Case study: Light emitting diode. Read the following paragraph and answer the questions. LED is a heavily doped P-N junction which under forward bias emits spontaneous radiation. When it is forward biased, due to recombination of holes and electrons at the junction, energy is released in the form of...
(i). Why are LEDs made of compound semiconductor and not of elemental semiconductors?
(ii) What should be the order of bandgap of an LED, if it is required to emit light in the visible range?
(iii) A student connects the blue coloured LED as shown in the figure. The LED did not glow when switch S is...
1. The V – I characteristics of a solar cell is shown in the figure. (a) What do the points P and Q represent? (b) Give the circuit diagram for a solar cell.
(i) Draw V-I characteristics of a p-n Junction diode. (ii) Differentiate between the threshold voltage and the breakdown voltage for a diode. (iii) Write the property of a junction diode which makes it suitable for rectification of ac voltages.
A point source of light is placed at the bottom of a tank filled with water, of refractive index $\mu$, to a depth d. The area of the surface of water through which light from the source can emerge, is : (a) $\frac{\pi d^2}{2(\mu^2-1)}$ (b) $\frac{\pi d^2}{(\mu^2-1)}$ (c) $\frac{\pi d^2}{\sqrt{2}\sq...
Why a photo-diode is operated in reverse bias whereas current in the forward bias is much larger than that in the reverse bias ? Explain. Mention its two uses.
(a) A p-type semiconductor is electrically neutral although it has holes as the majority carriers. Justify.
(a) In n-type semiconductor, explain how the crystal is electrically neutral although electrons are the majority carriers in it. (b) Write the conditions under which two light sources are said to be coherent.
How is the forward biasing different from the reverse biasing in a p-n junction diode? Name one device each which works under forward and reverse biasing.
How are (a) n-type semiconductor, and (b) p-type semiconductor obtained from an intrinsic semiconductor? Name the majority charge carriers in each of the semiconductors.
Briefly explain the generation and the separation of electrons and holes in a solar cell. Write two uses of solar cells.
Distinguish between the intrinsic semiconductor and the extrinsic semiconductor.
Differentiate between drift current and diffusion current in a p-n junction diode. What is the net current at the p-n junction in equilibrium ?
Explain the working of a light emitting diode. Write its two advantages over conventional incandescent low power bulbs.