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JEE physics MCQ

Electronics · CBSE STD 12 Science (CBSE - English Medium). 312 questions.

Questions · Page 2 of 7

MCQ

MCQ 511 Mark
Resistance of semiconductor at $0^{\circ} K$ is
  • A
    Zero
  • ✓
    Infinite
  • C
    Large
  • D
    Small
Answer
Correct option: B.
Infinite
At $0 K$ semiconductor behaves as insulator so it's resistance is infinite.
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MCQ 521 Mark
If $R_p=7 K \Omega, g_m=2.5$ millimho, then on increasing plate voltage by $50 V$, how much the grid voltage is changed so that plate current remains the same
  • ✓
    $-2.86\ V$
  • B
    $-4\ V$
  • C
    $+4\ V$
  • D
    $+2\ V$
Answer
Correct option: A.
$-2.86\ V$
$ \text { By using } \mu=-\frac{\Delta V_p}{\Delta V_g}=r_p \times g_m $
$ \Rightarrow 7 \times 10^3 \times 2.5 \times 10^{-3}=-\frac{50}{\Delta V_g}$
$ \Rightarrow \Delta V_g=-2.86 \mathrm{~V} .$
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MCQ 531 Mark
Which of the following energy band diagram shows the N-type semiconductor
  • A
    Image
  • ✓
    Image
  • C
    Image
  • D
    Image
Answer
Correct option: B.
Image
In $\mathrm{N}$-type semiconductor impurity energy level lies just below the conduction band.
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MCQ 541 Mark
Serious draw back of the semiconductor device is
  • ✓
    They cannot be used with high voltage
  • B
    They pollute the environment
  • C
    They are costly
  • D
     They do not last for long time
Answer
Correct option: A.
They cannot be used with high voltage
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MCQ 551 Mark
Which of these is unipolar transistor
  • A
    Point contact transistor
  • ✓
    Field effect transistor
  • C
    PNP transistor
  • D
    None of these
Answer
Correct option: B.
Field effect transistor
FET is unipolar.
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MCQ 561 Mark
In the $C B$ mode of a transistor, when the collector voltage is changed by $0.5$ volt. The collector current changes by $0.05\ mA$. The output resistance will be
  • ✓
    $10 \ k \Omega$
  • B
    $20\  k \Omega$
  • C
    $5\  k \Omega$
  • D
    $2.5 \ k \Omega$
Answer
Correct option: A.
$10 \ k \Omega$
Here $\Delta V_c=0.5 \mathrm{~V}, \Delta i_c=0.05 \mathrm{~mA}=0.05 \times 10 \mathrm{~A}$Output resistance is given by$R_{\text {out }}=\frac{\Delta V_c}{\Delta i_c}=\frac{0.5}{0.05 \times 10^{-3}}=10^4 \Omega=10 \mathrm{k} \Omega$
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MCQ 571 Mark
In case of a semiconductor, which of the following statement is wrong
  • A
    Doping increases conductivity
  • B
    Temperature coefficient of resistance is negative
  • C
    Resisitivity is in between that of a conductor and insulator
  • ✓
    At absolute zero temperature, it behaves like a conductor
Answer
Correct option: D.
At absolute zero temperature, it behaves like a conductor
At absolute zero temperature, semiconductor.
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MCQ 581 Mark
The relation between $\alpha$ and $\beta$ parameters of current gains for a transistors is given by
  • A
    $\alpha=\frac{\beta}{1-\beta}$
  • ✓
    $\alpha=\frac{\beta}{1+\beta}$
  • C
    $\alpha=\frac{1-\beta}{\beta}$
  • D
    $\alpha=\frac{1+\beta}{\beta}$
Answer
Correct option: B.
$\alpha=\frac{\beta}{1+\beta}$
$i_e=i_b+i_c \Rightarrow \frac{i_e}{i_c}=\frac{i_b}{i_c}+1$
$ \Rightarrow \frac{1}{\alpha}=\frac{1}{\beta}+1$
$ \Rightarrow\alpha=\frac{\beta}{(1+\beta)}$.
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MCQ 591 Mark
If $n$ and $v$ be the number of electrons and drift velocity in a semiconductor. When the temperature is increased
  • ✓
    $n$ increases and $v$ decreases
  • B
    $n$ decreases and $v$ increases
  • C
    Both $n$ and $v$ increases
  • D
    Both $n$ and $v$ decreases
Answer
Correct option: A.
$n$ increases and $v$ decreases
$n$ increases and $v$ decreases
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MCQ 601 Mark
For a transistor the parameter $\beta=99$. The value of the parameter $\alpha$ is
  • A
    $0.9$
  • ✓
    $0.99$
  • C
    $1$
  • D
    $9$
Answer
Correct option: B.
$0.99$
$\alpha=\frac{\beta}{1+\beta}=\frac{99}{1+99}=0.99$.
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MCQ 621 Mark
In a transistor configuration $\beta$-parameter is
  • A
    $\frac{l_b}{l_c}$
  • ✓
    $\frac{l_c}{l_b}$
  • C
    $\frac{l_c}{l_a}$
  • D
    $\frac{l_a}{l_c}$
Answer
Correct option: B.
$\frac{l_c}{l_b}$
$\beta=\frac{i_c}{i_b}$
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MCQ 631 Mark
Doping of intrinsic semiconductor is done
  • A
    To neutralize charge carriers
  • ✓
    To increase the concentration of majority charge carriers
  • C
    To make it neutral before disposal
  • D
    To carry out further purification
Answer
Correct option: B.
To increase the concentration of majority charge carriers
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MCQ 641 Mark
Which of the energy band diagrams shown in the figure corresponds to that of a semiconductor
  • A
    Image
  • B
    Image
  • C
    Image
  • ✓
    Image
Answer
Correct option: D.
Image
In semiconductors, the forbidden energy gap between the valence band and conduction band is very small, almost equal to $k T$. Moreover, valence band is completely filled where as conduction band is empty.
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MCQ 651 Mark
The valence band and conduction band of a solid overlap at low temperature, the solid may be
  • ✓
    A metal
  • B
    A semiconductor
  • C
    An insulator
  • D
    None of these
Answer
Correct option: A.
A metal
In conductors valence band and conduction band overlaps.
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MCQ 661 Mark
If no external voltage is applied across $P-N$ junction, there would be
  • A
    No electric field across the junction
  • ✓
    An electric field pointing from $N$-type to $P$-type side across the junction
  • C
    An electric field pointing from $P$-type to $N$-type side across the junction
  • D
    A temporary electric field during formation of $P-N$ junction that would subsequently disappear
Answer
Correct option: B.
An electric field pointing from $N$-type to $P$-type side across the junction
Across the $P-N$ junction, a barrier potential is developed whose direction is from $N$ region to $P$ region.
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MCQ 671 Mark
A semiconductor $X$ is made by doping a germanium crystal with arsenic $(Z=33)$. A second semiconductor $Y$ is made by doping germanium with indium $(Z=49)$. The two are joined end to end and connected to a battery as shown. Which of the following statements is correct
  • A
    (a) $X$ is $P$-type, $Y$ is $N$-type and the junction is forward biased
  • B
    (b) $X$ is $N$-type, $Y$ is $P$-type and the junction is forward biased
  • C
    (c) $X$ is $P$-type, $Y$ is $N$-type and the junction is reverse biased
  • ✓
    (d) $X$ is $N$-type, $Y$ is $P$-type and the junction is reverse biased
Answer
Correct option: D.
(d) $X$ is $N$-type, $Y$ is $P$-type and the junction is reverse biased
(d) Arsenic has five valence electrons, so it a donor impurity. Hence $X$ becomes $N$-type semiconductor. Indium has only three outer electrons, so it is an acceptor impurity. Hence $Y$ becomes $P$-type semiconductor. Also $N$ (i.e. $X$ ) is connected to positive terminal of battery and $P($ i.e. $Y)$ is connected to negative terminal of battery so $P N$-junction is reverse biased.
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MCQ 681 Mark
A $P-$type semiconductor can be obtained by adding
  • A
    Arsenic to pure silicon
  • ✓
    Gallium to pure silicon
  • C
    Antimony to pure germanium
  • D
    Phosphorous to pure germanium
Answer
Correct option: B.
Gallium to pure silicon
Gallium to pure silicon
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MCQ 691 Mark
The forbidden gap in the energy bands of germanium at room temperature is about
  • A
    $1.1 eV$
  • B
    $0.1 eV$
  • ✓
    $0.67 eV$
  • D
    $6.7 eV$
Answer
Correct option: C.
$0.67 eV$
$\Delta E_{g(\text { Germanium })}=0.67 \mathrm{eV}$
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MCQ 701 Mark
The charge on a hole is equal to the charge of
  • A
    Zero
  • ✓
    Proton
  • C
    Neutron
  • D
    Electron
Answer
Correct option: B.
Proton
The charge on hole is positive.
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MCQ 711 Mark
If the two ends $P$ and $N$ of a $P-N$ diode junction are joined by a wire
  • ✓
    There will not be a steady current in the circuit
  • B
    There will be a steady current from $N$ side to $P$ side
  • C
    There will be a steady current from $P$ side to $N$ side
  • D
    There may not be a current depending upon the resistance of the connecting wire
Answer
Correct option: A.
There will not be a steady current in the circuit
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MCQ 721 Mark
A full wave rectifier circuit along with the input and output voltages is shown in the figure Output voltageImage
Image
The contribution to output voltage from diode -2 is
  • A
    $A, C$
  • ✓
    $B, D$
  • C
    $B, C$
  • D
    $A, D$
Answer
Correct option: B.
$B, D$
In the positive half cycle of input ac signal diode $D$ is forward biased and $D$ is reverse biased so in the output voltage signal, $A$ and $C$ are due to $D$. In negative half cycle of lnput $a c$ signal $D$ conducts, hence output signals $B$ and $D$ are due to $D$.
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MCQ 731 Mark
If $n_e$ and $n_h$ are the number of electrons and holes in a semiconductor heavily doped with phosphorus, then
  • ✓
    $n_e>>n_h$
  • B
    $n_e\lt n_h$
  • C
    $n_e \leq n_h$
  • D
    $n_e=n_h$
Answer
Correct option: A.
$n_e>>n_h$
(a) Phosphorus is a pentavalent impurity so $n>n$.
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MCQ 741 Mark
The majority charge carriers in $P$-type semiconductor are
  • A
    Electrons
  • B
    Protons
  • ✓
    Holes
  • D
    Neutrons
Answer
Correct option: C.
Holes
In $P$-type semiconductors, holes are the majority charge carriers
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MCQ 751 Mark
If $N_P$ and $N_e$ be the numbers of holes and conduction electrons in an extrinsic semiconductor, then
  • A
    $N_{P} ! N_e$
  • B
    $N_P \quad N_e$
  • C
    $N_P \sim N_e$
  • ✓
    $N_{P} ! N_e$ or $N_P \sim N_e$
Answer
Correct option: D.
$N_{P} ! N_e$ or $N_P \sim N_e$
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MCQ 761 Mark
Resistivity of a semiconductor depends on
  • A
    Shape of semiconductor
  • ✓
    Atomic nature of semiconductor
  • C
    Length of semiconductor
  • D
    Shape and atomic nature of semiconductor
Answer
Correct option: B.
Atomic nature of semiconductor
Resistivity is the intrinsic property, it doesn't depend upon length and shape of the semiconductors.
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MCQ 771 Mark
In a semiconductor, the concentration of electrons is $8 \times 10^{14} / cm ^3$ and that of the holes is $5 \times 10^{12} cm ^3$. The semiconductor is
  • A
    $P$-type
  • ✓
    $N$-type
  • C
    Intrinsic
  • D
    PNP-type
Answer
Correct option: B.
$N$-type
Since $n>n$; the semiconductor is $N$-type.
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MCQ 781 Mark
Silicon is a semiconductor. If a small amount of $A s$ is added to it, then its electrical conductivity
  • A
    Decreases
  • ✓
    Increases
  • C
    Remains unchanged
  • D
    Becomes zero
Answer
Correct option: B.
Increases
Impurity increases the conductivity.
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MCQ 791 Mark
If the forward voltage in a semiconductor diode is doubled, the width of the depletion layer will
  • ✓
    Become half
  • B
    Become one-fourth
  • C
    Remain unchanged
  • D
    Become double
Answer
Correct option: A.
Become half
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MCQ 801 Mark
Wires $P$ and $Q$ have the same resistance at ordinary (room) temperature. When heated, resistance of $P$ increases and that of $Q$ decreases. We conclude that
  • A
    $P$ and $Q$ are conductors of different materials
  • B
    $P$ is $N$-type semiconductor and $Q$ is $P$-type semiconductor
  • C
    $P$ is semiconductor and $Q$ is conductor
  • ✓
    $P$ is conductor and $Q$ is semiconductor
Answer
Correct option: D.
$P$ is conductor and $Q$ is semiconductor
Conductor has positive temperature coefficient of resistance but semiconductor has negative temperature coefficient of resistance.
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MCQ 811 Mark
The impurity atoms which are mixed with pure silicon to make a $P$ type semiconductor are those of
  • A
    Phosphorus
  • ✓
    Boron
  • C
    Antimony
  • D
    Copper
Answer
Correct option: B.
Boron
Boron is trivalent.
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MCQ 821 Mark
The forbidden energy band gap in conductors, semiconductors and insulators are $E G_1, E G_2$ and $E G_3$ respectively. The relation among them is
  • A
    (a) $E G_1=E G_2=E G_3$
  • ✓
    (b) $E G_1
  • C
    (c) $E G_1>E G_2>E G_3$
  • D
    (d) $E G_1E G_3$
Answer
Correct option: B.
(b) $E G_1
(b) In insulators, the forbidden energy gap is very large, in case of semiconductor it is moderate and in conductors the energy gap is zero.
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MCQ 831 Mark
On increasing the reverse bias to a large value in a $P N$-junction diode, current
  • A
    Increases slowly
  • B
    Remains fixed
  • ✓
    Suddenly increases
  • D
    Decreases slowly
Answer
Correct option: C.
Suddenly increases
After a large reverse voltage is $P N$-junction diode, a huge current flows in the reverse direction suddenly. This is called Breakdown of $P N$-junction diode.
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MCQ 841 Mark
In the forward bias arrangement of a $P N$-junction diode
  • A
    The $N$ end is connected to the positive terminal of the battery
  • ✓
    The $P$ end is connected to the positive terminal of the battery
  • C
    The direction of current is from $N$-end to $P$-end in the diode
  • D
    The $P$ end is connected to the negative terminal of battery
Answer
Correct option: B.
The $P$ end is connected to the positive terminal of the battery
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MCQ 851 Mark
Which statement is correct
  • A
    N-type germanium is negatively charged and $P$-type germanium is positively charged
  • ✓
    Both $N$-type and $P$-type germanium are neutral
  • C
    N-type germanium is positively charged and $P$-type germanium is negatively charged
  • D
    Both $N$-type and $P$-type germanium are negatively charged
Answer
Correct option: B.
Both $N$-type and $P$-type germanium are neutral
SELF
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MCQ 861 Mark
Electrical conductivity of a semiconductor
  • A
    Decreases with the rise in its temperature
  • ✓
    Increases with the rise in its temperature
  • C
    Does not change with the rise in its temperature
  • D
    First increases and then decreases with the rise in its temperature
Answer
Correct option: B.
Increases with the rise in its temperature
With temperature rise conductivity of semiconductors increases.
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MCQ 871 Mark
The energy gap of silicon is $1.14\  eV$. The maximum wavelength at which silicon will begin absorbing energy is
  • ✓
    $10888 \mathring A$
  • B
    $1088.8 \mathring A$
  • C
    $108.88 \mathring A$
  • D
    $10.888 \mathring A$
Answer
Correct option: A.
$10888 \mathring A$
$\lambda_{\max }=\frac{h c}{E}=\frac{6.6 \times 10^{-34} \times 3 \times 10^8}{1.14 \times 1.6 \times 10^{-19}}=10888 \mathring A$
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MCQ 881 Mark
Three semi-conductors are arranged in the increasing order of their energy gap as follows. The correct arrangement is
  • ✓
    Tellurium, germanium, silicon
  • B
    Tellurium, silicon, germanium
  • C
    Silicon, germanium, tellurium
  • D
    Silicon, tellurium, germanium
Answer
Correct option: A.
Tellurium, germanium, silicon
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MCQ 891 Mark
In a triode amplifier, the value of maximum gain is equal to
  • A
    Half the amplification factor
  • ✓
    Amplification factor
  • C
    Twice the amplification factor
  • D
    Infinity
Answer
Correct option: B.
Amplification factor
The maximum voltage gain $(A)_{\sim}=\mu$ (Which is obtained when $R=\infty$ ).
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MCQ 901 Mark
The reverse biasing in a $P N$ junction diode
  • A
    Decreases the potential barrier
  • ✓
    Increases the potential barrier
  • C
    Increases the number of minority charge carriers
  • D
    Increases the number of majority charge carriers
Answer
Correct option: B.
Increases the potential barrier
In reverse biasing, width of depletion layer increases.
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MCQ 911 Mark
The slope of plate characteristic of a vacuum tube diode for certain operating point on the curve is $10^{-3} \frac{ mA }{ V }.$ The plate resistance of the diode and its nature respectively
  • A
    $100$ kilo-ohms static
  • ✓
    $1000$ kilo-ohms static
  • C
    $1000$ kilo-ohms dynamic
  • D
    $100$ kilo-ohms dynamic
Answer
Correct option: B.
$1000$ kilo-ohms static
$ \text { Plate resistance }=\frac{1}{\text { slope }}=\frac{1}{10^{-3} \times 10^{-3}}=10^6 \Omega$
$ =1000 \mathrm{k} \Omega \text { (static). }$
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MCQ 921 Mark
The valence of an impurity added to germanium crystal in order to convert it into a $P$-type semi conductor is
  • A
    $ 6$
  • B
    $ 5$
  • C
    $ 4$
  • ✓
    $3$
Answer
Correct option: D.
$3$
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MCQ 931 Mark
For a triode, at $V_g=-1$ volt, the following observations were taken $V_p=75 V , I_p=2 mA ,  V_p=100 V , I_p=4 mA$. The value of plate resistance will be
  • A
    $25 k \Omega$
  • B
    $20.8 k \Omega$
  • ✓
    $12.5 k \Omega$
  • D
    $100 k \Omega$
Answer
Correct option: C.
$12.5 k \Omega$
$r_p=\frac{V_{p_1}-V_{p_2}}{I_{p_1}-I_{P_2}}=\frac{75-100}{(2-4) \times 10^{-3}}=12.5 \times 10 \Omega=12.5 \mathrm{k} \Omega$.
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MCQ 941 Mark
If the amplification factor of a triode $(\mu)$ is 22 and its plate resistance is $6600 ohm$, then the mutual conductance of this valve is mho is
  • ✓
    $\frac{1}{300}$
  • B
    $25 \times 10^{-2}$
  • C
    $2.5 \times 10^{-2}$
  • D
    $0.25 \times 10^{-2}$
Answer
Correct option: A.
$\frac{1}{300}$
$\mu=r_p \times g_m \Rightarrow g_m=\frac{\mu}{r_p}=\frac{22}{6600}=\frac{1}{300}$.
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MCQ 951 Mark
In the circuit of a triode valve, there is no change in the plate current, when the plate potential is increased from $200$ volt to $220$ volt and the grid potential is decreased from $-0.5$ volt to $-1.3$ volt. The amplification factor of this valve is
  • A
    $15$
  • B
    $20$
  • ✓
    $25$
  • D
    $35$
Answer
Correct option: C.
$25$
$\mu=\frac{\left(V_{p_1}-V_{p_2}\right.}{\left(V_{G_1}-V_{G_2}\right)}=\frac{(200-220)}{(0.5-1.3)}=25$.
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MCQ 961 Mark
A triode has a mutual conductance of $2 \times 10^{-3} mho$ and an amplification factor of $50.$ The anode is connected through a resistance of $25 \times 10^3$ ohms to a $250$ volts supply. The voltage gain of this amplifier is
  • A
    $50$
  • ✓
    $25$
  • C
    $100$
  • D
    $12.5$
Answer
Correct option: B.
$25$
$ \text { Using } A_v=\frac{\mu}{1+\frac{r_p}{R_L}} \text { and } \mu=r_p \times g_m$
$\Rightarrow r_p=\frac{\mu}{g_m}=\frac{50}{2 \times 10^{-3}}=25 \times 10^3 \Omega $
$ \therefore A_v=\frac{50}{1+\frac{25 \times 10^3}{25 \times 10^3}}=25 .$
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MCQ 971 Mark
In P-type semiconductor, there is
  • A
    An excess of one electron
  • ✓
    Absence of one electron
  • C
    A missing atom
  • D
    A donar level
Answer
Correct option: B.
Absence of one electron
Absence of one electron, creates the positive charge of magnitude equal to that of electronic charge.
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MCQ 981 Mark
The unit of mutual conductance of a triode valve is
  • ✓
    Siemen
  • B
    $Ohm$
  • C
    Ohm metre
  • D
    Joule Coulomb
Answer
Correct option: A.
Siemen
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MCQ 991 Mark
A crystal diode is a
  • ✓
    Non$-$linear device
  • B
    Amplifying device
  • C
    Linear device
  • D
    Fluctuating device
Answer
Correct option: A.
Non$-$linear device
Non$-$linear device
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MCQ 1001 Mark
An oscillator is nothing but an amplifier with
  • ✓
    Positive feed back
  • B
    Large gain
  • C
    No feedback
  • D
    Negative feedback
Answer
Correct option: A.
Positive feed back
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MCQ - Page 2 - JEE physics STD 12 Science Questions - Vidyadip