Physics M.C.Q (1 Marks)

1. Due to rupture of bonds

Explanation:
When Zener diode is connected in reverse bias, as applied voltage reaches at Zener breakdown voltage, due to rupture of bonds there is a sudden increase in current in Zener diode.

1. The average energy of electrons and holes.

Explanation:
In an intrinsic semiconductor, n=p, where, n is number of electrons and p is number of holes in intrinsic semiconductor.
This implies that there is an equal chance of finding an electron at the conduction band edge as there is of finding a hole at the valence band edge. Thus, the average energy level of electrons and holes is half of the energy band gap in intrinsic semiconductors.
Also the Fermi energy level lie exactly in the middle of energy band gap in intrinsic semiconductors. Thus, the value indicated by Fermi energy level in an intrinsic semiconductor is the average energy of electrons and holes.

1. NOT

Explanation:
Only one logic gate has one input terminal i.e. NOT gate.

1. NAND and NOR

Explanation:
NAND and NOR gates are known as universal gates. Any one of these gates can be used to implement any kind of logic gate. This kind of feasibility is does not exist with other gates i.e. any other gate cannot solely implement all logic gates. For example, AND gate cannot be implemented using an OR gate and vice-versa. The implementation of NAND and NOR gates to generate other logic gates is shown above.

1. Stop a signal.

Explanation:
A NOT gate inverts the input signal which is the same as complementing a signal or changing the logic in a digital circuit. This means that when the input to the NOT gate is logic '0', the output is logic '1'. However, it does not stop a signal.

2. Statement 1-is true, statement -2 is true and statement -2 is correct explanation of statement-1.

Explanation:
NOT gate is also called invertor circuit since NOT gate inverts the input order. Hence, statement 1-is true statement-2 is true statement-2 is correct explanation of statement-1.

1. Photocurrent is proportional to incident light intensity.

Explanation:
In a photodiode, photocurrent is directly proportional to intensiy of incident light. More the incident light intensity, more will be the current produced.

4. Holes move from base to emitter.

4. Reverse biased

Explanation:
In reverse bias, 'p' region of a semi conductor is connected to negative pole and 'n' region to positive pole.

Solution:
Here, C = A.B and D = Ā.B
E = C + D = (A B) + (Ā .B)
Explanation The truth table of this arrangement of gates can be given 

A	B	Ā	C = A.B	d = Ā.B	E = (C + D)
0	0	1	0	0	0
0	1	1	0	1	1
1	0	0	0	0	0
1	1	0	1	0	0

1. There will not be a steady current in the circuit.

4. nh ≠ ne.

2. 0.3

Explanation:
The junction voltage Vo​ for a germanium diode is 0.3 V at room temperature. This potential opposes the diffusion of electrons from n-side and holes from p-side. It is 0.7 eV for Si at room temperature.

3. Rectification

Explanation:
The process by which ac is converted into dc is known as "Rectification".

4. None of these

Explanation:
Depletion region is a region near the p-n junction where flow of charge carriers (free electrons and holes) is reduced over a given period and finally results in zero charge carriers.The width of depletion region which is generally 1μm, depends on the amount of impurities added to the semiconductor. Impurities are the atoms (pentavalent and trivalent atoms) added to the semiconductor to improve its conductivity.
hence answer is 1μm and correct option is D - none of these.

1. 0,0

Explanation:
OR gate add the input signals given to it and AND gate multiply the input signals given to it.
Input (0,0) given to OR gate will yield result 0.
Now input for AND gate are (0,0) hence output will be 0.
For the second case, input (1,1) given to OR gate will yield result 1.
Now input for AND gate are (1,0) hence output will be 0.
Therefore combination of gates will yield result 0 and 0.

1. Electrons move from lower energy level to higher energy level in the conduction band.

3. Holes in the valence band move from higher energy level to lower energy level.

Solution:
As we apply electric field is applied across a semiconductor, the electrons in the conduction band acquire energy and get accelerated. They travel from lower energy level to higher energy level. While the holes in valence band travel from higher energy level to lower energy level, where they will be having more energy.

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

Explanation:
In Si and Ge at room temperature(300K); the energy band gap is low as the result of which electrons in the covalent bonds gain kinetic energy, they break the bond and move to conduction band.
A hole is also created in the valence band. So the number of free electrons for conduction is significant in Si and Ge.
The energy band gap in case of carbon is high as the result of which there are not significant number of electrons in the conduction band even at room temperature.

4. OR.

3. The electron concentration increases.

Explanation:
When a semiconductor is doped with a donor type such as arsenic or phosphorous, which has five valence electrons, the donor atom replaces the Si or Ge atom. As a result, four out of the five electrons of the donor atom form a covalent bond by sharing an electron with four atoms of silicon. However, the fifth electron is free to move. Also, due to the breaking up of covalent bonds at room temperature, equal number of electrons and holes are produced. Thus, the total number of holes in the n-type semiconductor is less compared to the number of free electrons.

1. Both inputs are 0.

Explanation:
The truth table for 2-input OR gate is as shown in the figure. Thus, the output is zero only when both inputs are zero.

4. Overlapping of valence and conduction bands.

Explanation:
In conductors, electrons are loosely bound to the nucleus hence, can detach easily at room temperature. Also, a large number of free electrons thus, available are conduction electrons. When the covalent bond breaks, electrons are freed from the atom.
The departure of an electron from valence band creates the vacancy in bond, this vacancy is known as hole. This hole is captured by another free electron.
Also, the energy level of free electrons corresponds to the conduction level, hence valance level and conduction level are overlapped. So there are no holes in conduction level to carry hole current.

1. Undoped

Explanation:
Doping is a process of adding impurities in a semiconductor. Doped semiconductors are known as extrinsic semiconductors and others are known as intrinsic ones.

3. Germanium

Explanation:
A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding.
As the valency of germanium is 4, it can share 4 electrons of neighboring atom to complete the octet.
Hence, Ge has covalent bond. NaCl is an example of an ionic bond and helium and copper both have valency 2 and 1 respectively.

4. 5eV

Explanation:
Forbidden energy gap, also known as band gap refers to the energy difference (eV) between the top of valence band and the bottom of the conduction band in materials. Current flowing through the materials is due to the electron transfer from the valence band to the conduction band.
Insulators do not conduct electricity because a large amount of energy is needed for the electrons to cross the forbidden energy gap. Moreover the forbidden energy gap is the widest (>5eV) in case of insulators.
Example: Forbidden energy gap in diamond is nearly 5.5eV.

2. Electron

Explanation:
In n-type semiconductor, large number of free electrons is present. Hence, free electrons are the majority charge carriers in the n-type semiconductor. The free electrons (majority charge carriers) carry most of the electric charge or electric current in the n-type semiconductor.

3. Increases

Explanation:
current increases as the resistance decreases, as zener current is inversely proportional to the series resistance.

4. All of these

Explanation:
Grown Junction Diode:

2. Holes and electrons

Explanation:
Depletion region of a p-n junction is formed due to the shortage of holes and electrons.

3. Computer

Explanation:
The number 0 is most important in digital communication where only two states 0,1 control the input and output and computer is based on digital signals.

1. Low at room temperature

Explanation:
In intrinsic semiconductors, n = p. Hence, at room temperature, no free electrons are available for conduction. If the temperature is increased, the covalent bonds will break and electrons will be freed, each electron will leave behind a hole and capture a new hole the process will continued and charge flows through intrinsic semiconductor.
Thus, its conductivity increases with temperature. Hence, in intrinsic semiconductor conductivity is low at room temperature.

3. Stabilisation.

2. Photoelectric effect

Explanation:
A transducer is an electronic device that converts light energy to electrical energy in television. When light falls on photosensitive element electric current is generated that is measured directly or after amplification. Similarly, photoelectric effect is the ejection of electrons from a metal or semiconductor surface when illuminated by light or any radiation of suitable wavelength.

2. Heavily doped junction diode.

Explanation:
The reverse breakdown voltage depends on doping of the diode. Hence, in the Zener diode the heavy doping of its p-n junction is done. The depletion region formed in the diode is very thin (<1 m) and the reverse bias voltage of about 5 V which is less than ordinary diode.

1. p type → n type

Explanation:
The holes in the covalent bonds of p-type semiconductor. They appear to move towards n-type semiconductor. Because the electrons in the covalent bonds of n-type semiconductor (not free electrons) jump towards p-type semiconductor due to plenty of holes available in the covalent bonds at p-side. 
Hence, conventional current flow from p-type to n-type.

2. Increases continuously with the forward current of the diode, reaches a maximum and then decreases.

Explanation:
The intensity of emitted light increase with the foreword current more the light intensity.

3. Collision generated charge carriers

Explanation:
When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown.
Avalanche breakdown occurs in reverse bias when the applied voltage is high enough, the free electron may move fast enough to knock other electrons free, creating more free-electron-hole pairs (i.e., more charge carriers), increasing the current.
Thus, the current flow in a Zener diode is mainly due to collision generated charge carriers.

2. Density of charge-carriers increases, but their mobilities decreases.

Explanation:
On increasing the temperature of a semi-conductor material, the density of charge increases which apparently increases the hinderance and thus decreases their mobility.

1. Electrons crossover from emitter to collector.

3. Electrons move from emitter to base.

Solution:
Key concept: Transistor:
A junction transistor is formed by sandwiching a thin layer of P-type semiconductor between two N-type semiconductors or by sandwiching a thin layer of N-type semiconductor between two p-type semiconductors.

E - Emitter (emits majority charge carriers)
C - Collects majority charge carries
B - base (provide proper interaction between E and C)

In normal operation base-emitter is forward biased, i.e., the positive pole of emitter base battery is connected to base and its negative pole is connected to the emitter. And collector base junction is reverse biased, i.e., the positive pole of the collector base battery is connected to collector and negative pole to base. Thus, electron moves from emitter to base and crossover from emitter to collector.

2. Doped impurity is high

Explanation:
Zener breakdown occurs due to heavily doped diodes.In this process electrons crosses the barrier from the valence band of the p-type to the conduction band of the lightly filled n-type material.

1. The diode is in its forward conducting state.

Explanation:
In a semiconductor diode, when diode in its forward conducting state current starts in diode and depletion region starts to deformed. After sometime depletion region is removed.

4. Base, collector and emitter.

4. All of the above

Explanation:
P-n junctions are an integral part of several optoelectronic devices. These include photodiodes, solar cells light emitting diodes (LEDs) and semiconductor lasers.

4. Negative.

3. emitter

Explanation:
 It is a p-n-p, transistor. The Lead marked with the arrow is the emitter. It tells the direction of the flow of the holes i.e, the flow of conventional current. 

1. NAND gate

Explanation:
The output is 0 only when the two inputs are 1.
The output is 1 when any of the input is zero. 
This is the characteristic of a NAND gate.

1. An insulator

Explanation:
Insulators have large energy gap between valence and conduction band (about 6eV), while semiconductors have a smaller one and conductors, the smallest energy gap.

1. Equal to

Explanation:
In an intrinsic semiconductor, the number density of electrons is equal to the number density of holes i.e ne = nh.
Since there is no doping, no extra hole or electron is produced.

3. Increases, decreases.

1. Ionisation by collision.

Explanation:
Avalanche breakdown is caused by impact ionization of electron-hole pairs. A very little current flows under reverse bias conditions and depletion region increases. The electric field in the depletion region of a diode can be very high. Electron/holes that enter the depletion region undergo a tremendous acceleration.
As these accelerated carriers collide with the atoms, they can knock electrons from their bonds, creating additional electron/hole pairs and thus additional current. As these secondary carriers are swept into the depletion region, they too are accelerated and the process repeats itself.

4. OR - Gate

Explanation:
OR gate has the property that output is one when any one of the inputs is one and zero only when all inputs are zero. From the truth table, it can be seen that the above two properties are satisfied.

2. 0

Explanation:
NOT gate yields the reverse of the input signal in output, thus when an input signal 1 is applied to a NOT gate, its output is 0.

1. Zero as no charges cross the junctions.

Explanation:
When a diode is connected in a Zero Bias condition, no external potential energy is applied to the PN junction. However if the diodes terminals are shorted together, a few holes (majority carriers) in the P-type material with enough energy to overcome the potential barrier will move across the junction against this barrier potential. This is known as the Forward Current.
Likewise, holes generated in the N-type material (minority carriers), find this situation favourable and move across the junction in the opposite direction. This is known as the Reverse Current and is referenced as IR. This transfer of electrons and holes back and forth across the PN junction is known as diffusion.
Then an Equilibrium or balance will be established when the majority carriers are equal and both moving in opposite directions so that the net result is zero current flowing in the circuit. When this occurs the junction is said to be in a state of Dynamic Equilibrium.

4. Number density of current carriers increases, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density.

Solution:
With increase in temperature, the number density of current carries increases, relaxation time decreases but effect of decrease in relaxation is much less than increase in number density. So, the conductivity of a semiconductor increases with increase in temperature.

2. Y exists when A exists or B exists or both A and B exist.

Explanation:
In Boolean algebra, A + B = Y implies that Y exists when A exists or B exists or both A and B exist.

3. Uncharged.

2. increased, increase

Explanation:
When the reverse voltage across a diode is very large, the valance electrons become free due to applied high electric field and get enough acceleration to make other electrons free, thus create a lot of electron-hole pairs in a short time. As the number of charge carriers increases, current also increases.
Therefore, at breakdown voltage, the rate of creation of hole-electron pairs is increased leading to the increase in current.

1. The valence band is partially empty and the conduction band is partially filled.

Explanation:
In semiconductors at room temperature the electrons get enough energy so that they are able to over come the forbidden gap. Thus at room temperature the valence band is partially empty and conduction band is partially filled.

3. The base has the least concentration of impurity.

3. Insulator.

4. Both (1) and (3) are true.

Explanation:
Glass is an insulator. The energy gap in a glass is greater than that of semiconductor and a good conductor.

4. OR gate

Explanation:
The image given shows a diode OR circuit. R is connected from the output to ground to provide bias current for the diodes. Any positive voltage will represent a logic 1 state and the summing of currents through multiple diodes does not change the logic level.

1. Increasing intensity without changing frequency.

Explanation:
Intensity of photons is the number of photons passing through a cross sectional area per unit time. Hence changing the intensity would cause change in number of ejected photoelectrons emitted by them.

4. p - n junction is electrically neutral.

Explanation:
Generally Si is a semiconductor. In p type semiconductor acceptor level lies near the valence band and each donor atom contribute one electron. p-n junction electrically neutral because total charge is zero.

3. Both drift and diffusion

Explanation:
Three important phenomena occurs during formation of pn junction:
Diffusion, Formation of space charge, Drift.

2. Cumulative effect of conduction band electron.

Explanation:
The avalanche breakdown in p-n junction is due to cumulative effect of conduction band electron. In reverse bias, due to applied electric field, electrons acquire enough energy to free more electron bound to the atom. The abundant number of electron-hole pairs are created for conduction, this is cumulative effect.

4. An artificially created particle.

4. 5eV.

2. From the p-side to the n-side.

Explanation:
When a p‒n junction is formed then because of the difference in the concentration of charge carriers in the two regions, electrons from the n region move to the p region and holes from the p region move to the n region. Since the direction of the current is always opposite to the motion of electron, the direction of the current is from the p side to the n side.
Similarly, when the junction is forward biassed, the positive terminal of the battery is connected to the pside of the p‒n junction and the negative terminal of the battery is connected to the n side of the p‒njunction. As a result, electrons in the n side of the p‒n junction are repelled by the negative terminal of the battery and they move to the p side, where the positive terminal of the battery attracts them. Similarly, holes from the p side of the p‒n junction are repelled by the positive terminal of the battery and they move to the n side, where the negative terminal of the battery attracts them. Thus, they give diffusion current from the p side to the n side across the p‒n junction.
In reverse biassing, there is no flow of majority carriers across the junction; hence, there is not diffusion current. Here, the flow of majority carriers is opposed by the applied voltage.

1. Eliminates a.c. component.

1. Work is a state finction.

Explanation:
Majority carrier in a n − type semiconductor are holes. This statement is false.
Since, in n−type semiconductor, the pentavalent impurity atoms donate electrons o the host crystal and the semiconductor doped with donars (pentavalent impurity) is called n − type semiconductor.
Therefore majority carrier in a n−type semiconductor are electrons.

1. Close to the valence band of the host crystal.

4. Forward bias, reverse bias.

1. Increases

Explanation:
The pure semiconductor has less number of thermally generated charge carriers. But when it is doped with pentavalent or trivalent impurity atoms, the number of charge carriers i.e. electrons and holes increases. So conductivity increases.

2. Breaking of covalent bonds

Explanation:
In intrinsic semiconductors, n = p. Hence, at room temperature, no free electrons are available for conduction.
If some energy is supplied to the atoms of intrinsic semiconductor, the covalent bonds will break and electrons will be freed, each electron will leave behind a hole and capture a new hole the process will continued and charge flows through intrinsic semiconductor.
Thus, in intrinsic semiconductor conductivity is due to breaking of covalent bonds.

2. Boron.

4. Aluminium.

Explanation:
A p-type semiconductor is formed by doping an intrinsic semiconductor with a trivalent atom (atom having valency 3). As phosphorous and boron have three valence electrons, they can be doped with silicon to make a p-type semiconductor.

3. intrinsic

Explanation:
At room temperature, in impure semiconductors some free charge carriers are available for conduction due to impurity atoms. But in pure, i.e., intrinsic semiconductors, n = p.
Hence, at room temperature no free electrons are available for conduction. If the temperature is increased the covalent bonds will break and electrons will be freed, each electron will leave behind a hole and capture a new hole the process will continued and charge flows through intrinsic semiconductor.
Thus, its conductivity is only due to breaking of covalent bonds.

2. Semi-conductors

Explanation:
Semiconductors in their natural state are poor conductors because a current requires the flow of electrons, and semiconductors have their valence band filled, preventing the entry flow of new electrons.
Thus semi-conductors allows a large current to pass through them.

1. NAND

Explanation:
The truth table of NAND gate is shown as above, which implies that if at least one of the input is low then the output is high.

2. A vacancy created when an electron leaves a covalent bond.

Solution:
Concept of holes in the semiconductor:

1. When an electron is removed from a covalent bond, it leaves a vacancy behind. An electron from a neighbouring atom can move into this vacancy, leaving the neighbour with a vacancy. In this way the vacancy formed is called a hole (or cotter), and can travel through the material and serve as an additional current carriers.
2. A hole is considered as a seat of positive charge, having magnitude of charge equal to that of an electron.
3. Holes acts as a virtual charge, although there is no physical charge on it.
4. Effective mass of hole is more than an electron.
5. Mobility of hole is less than an electron.

3. Uncharged.

Explanation:
A p-type semiconductor is formed by doping a pure semiconductor with a p-type material. As impurity atoms take the position of the germanium atom in a germanium crystal, three electrons of a p-type material form covalent bonds by sharing electrons with three neighbouring germanium atoms. However, the fourth covalent bond is left incomplete, with a want of one electron. This creates a hole. As the atom as a whole is neutral, the p-type material is also neutral.

1. Increasing the temperature.
2. Doping acceptor impurities.
3. Doping donor impurities.
4. Irradiating ultraviolet light on it.

Explanation:
We know that the conductivity of any semiconductor can be increased by increasing the number of charge carriers. All the given methods are effective in increasing the number of free charge carriers. Hence, all options are correct.

4. Conduction band is empty and valence band is filled with electrons.

Explanation:
Insulators are the materials which do not conduct electricity. All the electrons are filled in valance band whereas the conduction band is empty. Moreover, the energy band gap in insulators is very large, thus electrons cannot jump from valence band to conduction band.

1. Conductors

Explanation:
Free electron density is more in conductors that is why they are useful in conducting electricity.

3. n = p

Explanation:
Intrinsic semiconductors are pure ones. Hence there is no question of impurity. Valence band is the range of energy of electrons which are in the valence shell of the atoms of a substance. Conduction band is the range of energy of electrons which are free and available for conduction.
At room temperature, some electrons of intrinsic semiconductors get excited and reach the conduction band. During this process, the electrons leave empty spaces in the valence shell. These empty spaces are known as holes in a semiconductor. Number of free electrons (n) is equal to the number of holes (p).

3. a, c, d

Explanation:
a- represent OR gate 
b- represent the AND gate 
c- represent, the combination of OR and NOT gate, NOR gate.
d- represent, the combination of AND and NOT gate, NAND gate.

1. Minority carriers

Explanation:
When a diode is reverse biased, its depletion region increases in width. Thus depletion region would correspond to an insulator. However still some current actually flows through the depletion region. This is due to the pushing of minority carriers across the depletion region causing very small reverse 'leakage current'.

2. Statement 1-is true, Statement -2 is true and Statement -2 is correct explanation of Statement-1.

Explanation:
NAND or NOR gates are called universal gates or digital building blocks. Also, the repeated use of NAND (or NOR) gates can produce all the basis or any complicated gates can be formed using NAND (or NOR) gates. Hence, statement 1-is true statement -2 is true statement -2 is correct explanation of statement-1.

2. 0 and 75

Explanation:
Semiconductor can be used safely between temperature 0 and 75.

1. There will not be a steady current in the circuit.

Explanation:
In a p‒n junction, current flows only if it is connected to the battery. If two ends of a p‒n junction are joined by a wire, then there will be diffusion and drift currents in the circuit and they will cancel each other. Hence, no current will flow in the circuit.

3. A p-n junction

Explanation:
An ideal diode acts like an open switch when rivers biased and like a closed switch when forward biased.

3. 0 eV

Explanation:

1. If either one or both inputs are 1

Explanation:
At least one input required to activate or − gate

4. Is positively charged

Explanation:
The diffusion of electrons from n side to p side makes the n side of the depletion layer of pn junction positively charged since it becomes deficient in electrons and each side was neutral in the beginning.

2. Good conductor

Explanation:
In good conductors, the valance band and the conduction band overlap each other resulting in a zero band gap energy. Whereas, bandgap in insulator is nearly 5 eV and that in semiconductors is nearly 1.1eV.
Hence the given material is a good conductor.

3. C.B. is empty and V.B. is filled with electrons.

Explanation:
As shown in the image, insulators have a very large forbidden gap. Their conduction band is empty, thus they cannot conduct electricity under normal room temperature and pressure conditions. The valence band is full.

3. Germanium is doped with gallium.

Explanation:
A p-type semiconductor is produced by doping a 14 group element with a 13 group element as 14 group element has 4 valence electron whereas that of group 13 has 3 valence electron. We know that Germanium is a 14 group element and gallium is a 13 group element, thus doping germanium with gallium forms a p-type semiconductor.

4. Overlapped.

Explanation:
In conductors, electrons are loosely bound to the nucleus hence, can detach easily at room temperature also. A large number of free electrons thus, available are conduction electrons.
The energy level of these electrons corresponds to the conduction level, hence valance level and conduction level are overlapped.

1. Silicon

Explanation:
Semiconductors are made of Si, generally. Because Si is the second most abundant element in earth's crust after oxygen and is less expensive than other semiconductors used in intrinsic semiconductors. 

2. Can be combined to produce OR, AND and NOT gates.

2. 6 eV

Explanation:
Atoms are neutral in the insulator, thus there are no valence electrons in the outer orbit. The electrons are tightly bound with the nucleus hence, at room temperature thermal energy is not enough to push the electrons into conduction band and hence, no electrons are available for conduction.
The energy required for electron to escape out from orbit and to over come the energy gap is thus of the order of 6 eV.

4. The conduction band is empty and the valence band is filled with electrons.

Explanation:
In insulators, the electrons are very tightly bound to the nucleus. At a room temperature, thermal energy is not enough to push electrons into conduction band. The energy band gap is very high. Thus the conduction band is empty and the valence band is filled with electrons.

1. The notion that it is a whole lot easier to keep track of the missing particles in an "almost-full" band.

Explanation:
The concept of holes was introduced so as to occupy the empty spaces left by the missing electron. For example, in a valence band, when an electron jumps from valence to conduction band, an empty space is created in valence band which is occupied by a hole.

3. 1eV.

1. 0 eV

Explanation:
Forbidden band gap is the group of energy levels that cannot be occupied by the electrons, these energies lies in between conduction band and valence band. In pure conductors, electrons are loosely bound to the nucleus hence, can detach easily at room temperature also.
A large number of free electrons thus, available are conduction electrons. The energy level of these electrons corresponds to the conduction level, hence valence level and conduction level are overlapped.
Due to this, there is no forbidden band gap present in between conduction band and valence band hence, for metals the forbidden band gap is 0 eV.

2. 0.71eV.

1. They flow from positive terminal to negative terminal.

Explanation:
Electrons flow from negative to positive terminal of battery. whenever the electric current flows from positive terminal of battery to negative terminal of battery is called conventional current. the conventional current has same direction of flow of holes but opposite to direction of flow of from electron.

1. Metal oxides with high temperature coefficient of resistivity.

1. Covalent bond

Explanation:
Semi-conductors are made of 14th Group elements which form covalent bonding.

2. Boron.

4. For increasing the amplitude of an AC signal

Explanation:
To increase the amplitude of an AC signal, transistors are used. p-n junction diodes can be used as rectifiers and in photo-diode and LED.

3. A-1 B-0 C-1

Explanation:
Logic gate OR is used for addition of the input signals and Logic gate AND is used for multiplication of the input signals. Hence, here inputs A = 1, B = 0 and C = 1 will yield the output Y = 1.

3. A bond is broken on the n-side and the electron freed from the bond jumps to a broken bond on the p-side to complete it.

Explanation:
A hole diffuses from the p side to the n side in a p−n junction; that is, an electron moves from the n side to the p side. This implies that a bond is broken on the n side. As the electron travels towards the p side, which is rich in holes, it combines with a hole. A hole is created because of the deficiency of one electron. So, when an electron combines with a hole, it completes that bond.

4. 0 + 0 = 1

Explanation:
In the Boolean algebra, binary addition is given as:
1 + 0 = 1
0 + 1= 1
1 + 1 = 1
Hence, 0 + 0 =1 is wrong.

3. 1.1 = 0

Explanation:
In the Boolean algebra,
1.0 = 0
0.1 = 0
1.1 = 1

4. Concentration of positive and negative charges near the junction.

Explanation:
During the formation of a junction diode, holes from p- region diffuse into n-region and electrons from n-region diffuse into p-region.
In both cases, when an electrons meets a hole, they cancel the effect at each other and as a result, a thin layer at the junction becomes free from any of charges carriers. This is called depletion layer.
There is a potential gradient in the depletion layer, negative on the p-side, and positive on the n-side.
The potential difference thus developed across the junction is called potential barrier.

3. Operating in the breakdown region

Explanation:
The zener voltage will be a constant only when it is operating in the breakdown region.

3. Insulators

Explanation:
In insulators, the electrons are tightly bound with the nucleus hence, at room temperature thermal energy is not enough to push the electrons into conduction band and hence, no electrons are available for conduction.
The energy required for electron to escape out from orbit and to over come the energy gap is thus of the order of 6 eV, while for semiconductors and conductors it is (of the order of) 1 eV and 0 respectively.

1. Large velocity of the minority charge if the doping concentration is small.

Explanation:
When it comes to he breakdown in a reverse biased PN junction diode, it will probably happen only because of the accumulation of the higher charge at the biased region and large velocity of the minority charge if the doping concentration is small. This is the main cause the breakdown.

2. NOR

Explanation:
The symbol of circle shown in figure with OR gate indicates the NOT gate hence, given gate is NOR gate.

1. Majority carriers

Explanation:
P-type semiconductors are those which have a p-type impurity. A p-type impurity is a material in which the atoms have only 3 Valence Electrons. When they are added to a pure semiconductor, each atom gets bonded with 3 of atoms of the semiconductor. Between the 4th atom of the semiconductor and the atom of the impurity, there is an empty space due to lack of an electron. This empty space is known as a hole. Because of a large existence of P-type material in a p-type semiconductor, it has more holes as compared to free electrons. Hence holes are majority carriers.

4. Relative widths of their energy gaps

Explanation:
According to band theory, distinction between conductors, insulators and semiconductors is based on relative width of energy gaps between valence band and conduction band.

1. N-side to the p-side.

1. Metallic conductors

Explanation:
When an electric field is applied across the metallic conductors the randomly moving electrons are subjected to electrical forces along the direction of the field. Due to this field, the electrons do not give up their randomness of motion, but they will be shifting towards higher potential. That means the electrons will drift towards higher potential along with their random motions.
In semiconductors, in addition to electrons, the travelling vacancies in the valence-band electron population (called 'holes'), act as mobile positive charges and are treated as charge carriers. Electrons and holes are the charge carriers in semiconductors.
Hence, electric current is due to drift of electrons in metallic conductors.

2. Less than that in a insulator.

Explanation:
The energy band gap is the energy difference between 2 bands i.e. valence band and the conduction band. In case of conductors, energy band gap is very small almost overlapping whereas, in case of insulators, the band gap is ∼6 eV. So. band gap of conductors is less than insulators.

2. Circuit 2 and circuit 3.

Explanation:
In circuit 1, one diode is forward biassed and the other diode is reverse biassed. The forward-biassed diode offers zero resistance (ideally) to the current flow, so it can be replaced by a short circuit. The voltage drop across the first diode will be zero. The second diode is reverse biassed, so it can be replaced by an open circuit; hence, the voltage drop across this diode will be maximum.
In circuit 2, both the diodes are forward biassed, so they can be replaced by short circuits; hence, the voltage drop across both of them will be minimum and equal.
In circuit 3, both the diodes are reverse biassed, so both can be replaced by open circuits; hence, the voltage drop across both of them will be maximum and equal.

2. Holes and conduction electrons systematically go from the p-side to the n-side and from the n side to the p-side respectively.
3. There is no net charge transfer between the two sides.
4. There is a constant electric field near the junction.

Explanation:
Because of the difference in the concentration of charge carriers in the p−n junction, holes from the p side move to the n side and electrons from the n side move to the p side. This motion of charge carriers gives rise to diffusion current.
Because of this, a negative space charge region is formed in the p region and a positive space region is formed in the n region. This sets up an electric field across the junction. Thus, there is a constant electric field near the junction.
This electric field further opposes the diffusion of majority charge carriers across the junction. As a result, an electron from the p region starts moving to the n region and a hole from the n region starts moving to the p region. This sets up drift current. Thus, there is a systematic flow of charge carriers across the junction. Also, there is no net charge transfer between the two sides.

1. Increases..

Explanation:
When an impurity (either a p-type atom or an n-type atom) is doped into an intrinsic semiconductor, it increases the number of charge carriers in the intrinsic semiconductor. As conductivity is directly related to the number of charge carriers, the conductivity of a semiconductor increases with doping.

3. 0.93

4. 4

Explanation:
The valency of semiconductor (Ge or Si) is four, hence it has 4 valence electrons in the outermost orbit of the Ge or Si-atom

3. A co-valent bond is broken due to thermal energy, the removal of one electron leaves a vacancy.

Explanation:
Holes are created when a co-valent bond is broken due to thermal energy. The removal of one electron leaves a vacancy known as a hole.

3. Close to the conduction band of the host crystal.

1. Cuprous oxide

Explanation:
Iron, Copper, Aluminium are metals and are therefore conductors whereas Cuprous oxide is a semiconductor.

3. Both A and B

Explanation:
Optoelectronic devices and components are those electronic devices that operate on both light and electrical currents. This can include electrically driven light sources such as laser diodes and light-emitting diodes, components for converting light to an electrical current such as solar and photovoltaic cells and devices that can electronically control the propagation of light.

4. High doping.

Explanation:
Zener breakdown occurs in heavily doped p-n junctions. The heavy doping makes the depletion layer extremely thin. So that, carriers cannot accelerate enough to cause ionization. Thus, current will increase in reverse bias only due to reverse breakdown voltage.

2. From the p-side to the n-side

Explanation:
Holes from p-type diffuse into the n-type and electrons from n-type diffuse into the p-type due to concentration gradient to form a depletion region which results in the rise of diffusion current flowing from p to n side.

4. Volatge regulation

Explanation:
 A voltage regulator circuit can be designed using a zener diode to maintain a constant DC output voltage across the load in spite of variations in the input voltage or changes in the load current.

3. Missing electron in valence band

Explanation:
A hole is not itself a physical quantity but a missing electron in valence band. An electron from adjacent site jumps to fill this hole and thus creates a hole at its former site. So it seems as if the hole itself has moved.

1. Output Y exists when both inputs A and B exist.

4. Higher voltage level

Explanation:
In digital logic, higher voltage is defined as logic state '1' and lower voltage is defined as logic state '0'. The higher voltage need not necessarily be positive. For example, it is possible that state '0' is defined as −10 V and state '1' is defined as −5 V.

2. Integrated circuit

Explanation:
Integrated circuits or I.C's are those semi-conductor device with both active and passive electronic elements diffused into a silicon water to form a functional circuit.

4. P-n junction diode.

2. p-n junction diode near threshold voltage.

Explanation:
p−n junction diode near threshold voltage is used as a square law device for modulation.

1. There are no free electrons at 0K.

3. The number of free electrons increases with temperature.
4. The number of free electrons is less than that in a conductor.

Explanation:
In semiconductors, the valence band is full at 0K, but the conduction band is empty. So, no free electron is available for conduction at 0K.
As the temperature increases, covalent bonds that provide free charge carriers for conduction in a semiconductor break.
As the conduction band in metals is already partially filled at 0K, many free electrons below the Fermi level acquire energy from an external source or temperature, jump to the conduction band and start behaving like free electrons. Hence, metals contain more free electrons than semiconductors.

3. Gallium Arsenide

Explanation:
Direct Band gap: Defined when maximum energy in the valence band and minimum energy in the conduction band occurs at the same values of the crystal momentum i.e, a direct transition of electrons from valence to conduction band takes place.

4. 4

4. All of the above

Explanation:
LEDs have longer life as compared to incandescent lamps. LED require low operational voltage and less power as compared to incandescent lamps. LEDs also have fast on-off switching capabilities.

4. Quasicrystals.

Explanation:
Aluminum gallium arsenide, indium gallium arsenide, and gallium arsenide are used in Laser diodes, LEDs, whereas Quasicrystals have poor heat conductivity which makes them good insulators, so not used in electronic devices.

2. 1.1

Explanation:
The forbidden gap or band gap for pure Si is 1.1 eV.

1. Forward biased.

Explanation:
An LED is a light emitting diode. The LED emits light when it is forward biased and it emits no light when it is reverse biased. The intensity of light is proportional to the square of the current flowing through the device.
When a junction diode is forward biased, energy is released at the junction due to recombination of electrons and holes. In the junction diode made of gallium arsenide or indium phosphide, the energy is released in visible region. Thus, light is emitted form the diode and hence the name 'light emitting diode'.

1. High potential at N side and low potential at P side.

Explanation:

3. Y exists when both A and B exist but not when only A or B exists

Explanation:
In Boolean algebra A.B = Y implies that Y exists when both A and B exist but not when only A or B exists.

2. Regulator

Explanation:
Zener diode is used to supply constant voltage in voltage regulator circuit.

1. From the n-side to the p-side.

Explanation:
After the diffusion of majority charge carriers across a p‒n junction, an electric field is set up because of the accumulation of immobile ions at the junction. These further oppose the motion of majority charge carriers across the junction. As a result, electrons from the p region start moving to the n region and holes from the n region start moving to the p region. This constitutes the drift current. As the direction of the current is opposite to the direction of the motion of the electrons, the direction of the drift current is from the n side to the p side.
In forward biasing, there is no movement of electrons from the p region to the n region and of holes from the n region to the p region. Hence, there is not drift current.

1. If the junction is forward-biased.

Explanation:
In the forward biassing of a p−n junction, the positive terminal of the battery is connected to the p side of the p−n junction and the negative terminal of the battery is connected to the n side of the p−n junction. As a result, electrons in the n side of the p−n junction are repelled by the negative terminal of the battery and move to the p side, where the positive terminal of the battery attracts the electrons. Similarly, holes from the p side of the p−n junction are repelled by the positive terminal of the battery and move to the nside, where the negative terminal of the battery attracts the holes. Thus, they give diffusion current across the p−n junction.
In case of reverse biassing, no conduction takes place across the junction because of the diffusion of majority carriers. Hence, there is no diffusion current.
If the junction is unbiased, then diffusion current is initially maximum. But at equilibrium, diffusion current becomes equal to drift current.

1. There are no free electrons at 0 K.

3. There will be more free electrons than holes in the semiconductor.

3. The valence band is completely filled and the conduction band is partially filled.

1. New holes and conduction electrons are produced continuously throughout the material.

4. Holes and conduction electrons recombine continuously throughout the material except in the depletion region.

Explanation:
In a p‒n junction diode, diffusion current flows because of the diffusion of holes from the p side to the n side and of electrons from the n side to the p side. The current flowing in the diode due to the diffusion of charge carriers across the junction is called the diffusion current. The current flowing in the diode due to the movement of minority carriers across the junction due to their thermal energy is called the drift current. In an unbiased diode, the net current flowing across the junction is zero due to the cancellation of the drift current by the diffusion current. For the flow of diffusion and drift currents, holes and electrons are produced continuously throughout the material. When a hole crosses the junction, it combines with an electron on the n side. As the depletion region is devoid of free charge carriers, this recombination never takes place inside the depletion region.

2. It is equivalent to series switching circuit.

Explanation:
AND gate is only active when both the inputs are high same as series switching circuit which is active only when both switches are closed.

3. Conduction band

Explanation:
The band gap in case of semiconductors is of order 3−4 eV. At absolute zero, the valence band is filled and conduction band is empty, so it behaves as an insulator. As the temperature is raised, electrons in the valence band gain sufficient energy to overcome the band gap and jump to the conduction band.

2. Liquid Crystal Display
   Explanation:
   LCD stands for "Liquid Crystal Display".

LCD is a special thin flat panel that can let light go through it, or can block the light. (Unlike an LED it does not produce its own light).
The panel is made up of several blocks, and each block can be in any shape. Each block is filled with liquid crystals that can be made clear or solid, by changing the electric current to that block.

3. Rectifier

Explanation:
Diode can work as rectifier, While converting AC voltage to DC voltage, we use 4 diodes in the form of wheat stone bridge,It effectively works as rectifier.

2. 1 hole is created

Explanation:
For one electron vacancy, an empty space or void is created. In order to fill that empty space, a charge carrier with a charge equal in magnitude but opposite polarity should occupy that space in order to maintain electrical neutrality. Such a charge particle is called a hole.

1. pn junction

Explanation:
As pentavalent impurities contribute or donate electrons to the semiconductor, these are called donor impurities and similarly as these impurities contribute negative charge carriers in the semiconductor this we refer as n - type impurities. The semiconductor doped with n - type impurities is called n-type semiconductor.
Since trivalent impurities contribute excess holes to semiconductor crystal, and these holes can accept electrons, these impurities are referred as acceptor impurities. As the holes virtually carry positive charge, the said impurities are referred as positive - type or p - type impurities and the semiconductor with p type impurities is called p-type semiconductor.

3. Copper strip decreases and that of germanium increases.

4. All are correct conclusion about elements A, B, C and D

Explanation:
Energy gaps between the highest band and the lowest empty bands is lowest in metals, moderate in semi conductors and very high in insulators. This suggests us that:
Element A must be a metal, element C must be an insulator and element B and D can be semiconductors.

As the intrinsic semiconductor is free from all impurities, the number of electrons is equal to the number of holes.

3. Germanium

Explanation:
Energy gap of most of the semiconductors is nearly 1.1eV which is less than 3eV.
As we know germanium is a semiconductor and its energy gap is 0.67eV. Thus germanium is the right answer.

2. Hole

Explanation:
Whenever an electron jumps from a valence band to conduction band, an equal and opposite charge is left behind in the place of an electron. This is called a hole.

3. An unfilled covalent bond.

Explanation:
When the covalent bond breaks, electrons are freed from atom. The departure of electron from valence band creates vacancy in bond, this vacancy is known as hole. Hence, a hole is an unfilled covalent bond.

2. Cancels the potential barrier.

2. Infinity.

4. They require low energy to continue their motion.

2. The photodiode has to be reversed biased.

Explanation:
Photo diode is used to detect light.
In reverse biased condition, the width of depletion region increases as the the applied reverse bias voltage increases across the diode. So, by applying a larger voltage, more of the incident photons are converted to electric current thereby increasing the efficiency.
In forward biased condition, the width of depletion region decreases so only a small portion of the incident photons get converted to electric current and hence the efficiency is less.
Hence photo diode in reverse biased condition detects light.

4. A p-n junction.

Explanation:
As a p−n junction allows the flow of current in forward bias and stops the current in reverse bias (almost negligible reverse leakage current flows in the reverse-biassed p−njunction), the device should be a p−n junction. Other options are examples of semiconductors that allow moderate current to flow and that do not have any effect of changing the polarity of the battery.

2. OR gate followed by NOT gate.

Explanation:
Truth table of NOR is complement of OR. That's why NOR is combination of OR gate followed by NOT gate.

3. Both electrons and holes.

1. +ve terminal to p and -ve terminal to n

Explanation:
To forward bias the p-n junction, the p side is made more positive, so that it is "downhill" for electron motion across the junction. An electron can move across the junction and fill a vacancy or "hole" near the junction. It can then move from vacancy to vacancy leftward toward the positive terminal, which could be described as the hole moving right. The conduction direction for electrons in the diagram is right to left, and the upward direction represents increasing electron energy.

2. Reverse bias

Explanation:
We know that zener diode works on the reverse bias. When the reverse bias is equal to the break-down voltage, the voltage across the zener remains almost constant and the current increases rapidly.

4. NOR

Explanation:
The truth table for NOR gate is shown above which suggests that NOR gate is the logic gate which produces low output when any of the inputs is high.

4. NOR

Explanation:
NAND gate is considered universal gate. As other gates can be formed from this gate.

3. They cannot be used with high voltage.

2. non-ohmic resistance

Explanation:
We know that in the case of metallic conductors, the potential difference varies in direct proportion to the current flowing. The I−V graph of a ohmic conductor is a straight line. But, a p-n junction diode is not in according with Ohm's law. The current voltage characteristic curve of a p-n junction diode shows both forward bias as well as reverse bias characteristics as shown as in the graph.

2. The presence of holes

Explanation:
In the valence band, current is only due to holes. In the conduction band, current is due to electrons.

3. Stabilisation

Explanation:
A zener diode is always operated in its reverse biased condition. A voltage regulator circuit can be designed using a zener diode to maintain a constant DC output voltage across the load in spite of variations in the input voltage or changes in the load current. The zener voltage regulator consists of a current limiting resistor RS​ connected in series with the input voltage VS​ with the zener diode connected in parallel with the load RL in this reverse biased condition.Hence we can say that ,zener diode is used for stabilization.

4. All of the above.

3. Photo-voltaic effect

Explanation:
The generation of current or voltage in a material, when exposed to light is called photovoltaic effect.
The device which operates on this effect is called photo-voltaic device or solar cell. It is a p-n junction diode which converts solar energy into electrical energy.

1. An electron hole

Explanation:
A hole is an absence of an electron in a particular place in an atom. Although it is not a physical particle, a hole can be passed from atom to atom in a semiconductor material.

1. It is a constant voltage device.

Explanation:
Zener diode is a p-n junction diode working in the breakdown region. It is used as a voltage regulator/stabilizer to provide a constant voltage from a source whose voltage may fluctuate over a wide range.

3. Majority carriers in both regions.

4. NAND

Explanation:
NAND and NOR gates are the basic building blocks of the digital circuit which means that all other gates can be synthesized using NAND (or NOR) gate only.

3. A+B+C+D

Explanation:

3. Depletion region

Explanation:
In depletion region negative charge carrier electrons are attached with their positive charge carrier holes. hence there is no free charge carriers exists.

2. Potential barrier across junction increases.

1. Leakage current.

4. 199

C