Electronic Devices Chapter-Wise Test 7

Correct answer Carries: 4.

Wrong Answer Carries: -1.

The forward current in a p-n junction diode increases significantly beyond:

The forward current rises exponentially after the applied voltage exceeds the threshold (cut-in) voltage, reducing the barrier height significantly.

Threshold voltage
Breakdown voltage
Reverse saturation point
Equilibrium potential
1

The resistivity of a semiconductor typically lies in the range:

Semiconductors have intermediate resistivity between metals and insulators, typically ranging from \( 10^{-5} \) to \( 10^6 \, \Omega \, \text{m} \).

\( 10^{-2} \) to \( 10^{-8} \, \Omega \, \text{m} \)
\( 10^{10} \) to \( 10^{19} \, \Omega \, \text{m} \)
\( 10^{-5} \) to \( 10^6 \, \Omega \, \text{m} \)
\( 10^5 \) to \( 10^8 \, \Omega \, \text{m} \)
3

In a reverse-biased p-n junction, the effective barrier height is:

In reverse bias, the applied voltage (\( V \)) adds to the built-in potential (\( V_0 \)), increasing the effective barrier height to \( V_0 + V \).

\( V_0 - V \)
\( V \)
\( V_0 \)
\( V_0 + V \)
4

In a p-type semiconductor, the acceptor impurities create:

Trivalent acceptor impurities (e.g., B, Al) in a p-type semiconductor lack one electron per atom, creating holes that act as majority carriers by accepting electrons from the lattice.

Extra electrons
Holes
Positive ions only
Neutral atoms
2

A pure Si crystal is doped with 1 ppm of pentavalent impurity. If the Si atom density is \( 5 \times 10^{28} \, \text{m}^{-3} \), the number of donor atoms per cubic meter is:

1 ppm = 1 part per million = \( 10^{-6} \). Number of donor atoms = \( 10^{-6} \times 5 \times 10^{28} = 5 \times 10^{22} \, \text{m}^{-3} \). These contribute electrons, assuming full ionization at room temperature.

\( 5 \times 10^{20} \, \text{m}^{-3} \)
\( 5 \times 10^{24} \, \text{m}^{-3} \)
\( 5 \times 10^{26} \, \text{m}^{-3} \)
\( 5 \times 10^{22} \, \text{m}^{-3} \)
4

The maximum number of electrons that can occupy the outer orbit of a Si atom is:

The outer orbit of Si (third shell) can hold 8 electrons (2s + 6p), though Si has only 4 valence electrons naturally forming covalent bonds.

4
6
2
8
4

A silicon diode has a threshold voltage of approximately:

The threshold or cut-in voltage for a silicon diode is about 0.7 V, beyond which the forward current increases significantly.

0.2 V
0.5 V
1.0 V
0.7 V
4

In an intrinsic semiconductor, the number of free electrons (\( n_e \)) is equal to:

In an intrinsic semiconductor, thermal excitation generates equal numbers of free electrons (\( n_e \)) and holes (\( n_h \)), so \( n_e = n_h = n_i \), where \( n_i \) is the intrinsic carrier concentration.

Number of holes (\( n_h \))
Twice the number of holes
Half the number of holes
Zero
1

In an intrinsic semiconductor, the total current is the sum of:

The total current (\( I \)) in an intrinsic semiconductor is the sum of electron current (\( I_e \)) and hole current (\( I_h \)), i.e., \( I = I_e + I_h \).

Diffusion and recombination currents
Drift and recombination currents
Electron and hole currents
Diffusion and drift currents
3

Which material among Si, Ge, and Sn behaves as a metal?

Sn (tin) has an energy gap of 0 eV, typical of metals with overlapping bands, unlike Si (1.1 eV) and Ge (0.7 eV), which are semiconductors.

Si
Ge
C
Sn
4

In forward bias, the effective barrier height of a p-n junction is:

In forward bias, the applied voltage (\( V \)) opposes the built-in potential (\( V_0 \)), reducing the effective barrier height to \( V_0 - V \), allowing more carriers to cross the junction.

\( V_0 + V \)
\( V_0 - V \)
\( V_0 \)
\( V \)
2

In an n-type semiconductor, the donor impurities contribute:

Pentavalent donor impurities (e.g., As, P) in an n-type semiconductor donate extra electrons for conduction, significantly increasing the number of free electrons beyond intrinsic levels.

Extra electrons
Extra holes
Positive ions only
Negative ions only
1

In an intrinsic semiconductor, the hole movement is due to:

Hole movement is a result of electrons jumping between covalent bonds, creating an apparent motion of the vacancy (hole) in the opposite direction, under an electric field or diffusion.

Free electron drift
Ionic displacement
Electron jumps in bonds
Thermal generation only
3

In a full-wave rectifier, the number of diodes typically used with a centre-tap transformer is:

A full-wave rectifier with a centre-tap transformer uses two diodes, each conducting during alternate half-cycles, to rectify both positive and negative halves of the AC input.

1
3
4
2
4

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