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## Questions and Answers

A silicon specimen is made into a P-type semiconductor by doping, on average, one Indium atom per $5 imes 10^7$ silicon atoms. If the number density of atoms in the silicon specimen is $5 imes 10^{28}$ atoms/mÂ³, then the number of acceptor atoms in silicon per cubic centimeter will be:

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The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature:

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The typical ionization energy of a donor in silicon is:

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In a PN-junction diode, the reverse saturation current is $10^{-5}$ amp at 27 Â°C. The forward current for a voltage of 0.2 volts is:

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When a potential difference is applied, the current passing through:

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A 2V battery is connected across the points A and B. Assuming that the resistance of each diode is zero in forward bias and infinity in reverse bias, the current supplied by the battery when its positive terminal is connected to A is:

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In the circuit, if the forward voltage drop for the diode is 0.5V, the current will be:

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A P-type semiconductor has acceptor levels 57 meV above the valence band. The maximum wavelength of light required to create a hole is:

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Current in the circuit will be:

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The diode used in the circuit has a constant voltage drop of 0.5 V at all currents and a maximum power rating of 100 milliwatts. What should be the value of the resistor R, connected in series with the diode for obtaining maximum current?

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For a transistor amplifier in common emitter configuration for load impedance of 1 kÎ© (hfe = 50 and hoe = 25 ÂµA/V), the current gain is:

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In the following common emitter configuration, an NPN transistor with current gain Î² = 100 is used. The output voltage of the amplifier will be:

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In semiconductor, the concentrations of electrons and holes are $8 imes 10^{18}/m^3$ and $5 imes 10^{18}/m^3$ respectively. If the mobilities of electrons and holes are $2.3 m^2/volt-sec$ and $0.01 m^2/volt-sec$ respectively, then the semiconductor is:

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A sinusoidal voltage of peak value 200 volts is connected to a diode and resistor R in the circuit. If the forward resistance of the diode is negligible compared to R, the RMS voltage (in volts) across R is approximately:

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The junction diode in the circuit requires a minimum current of 1 mA to be above the knee point (0.7 V) of its I-V characteristic curve. If VB = 5 V, then the maximum value of R so that the voltage is above the knee point will be:

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In the given circuit, V(t) is the sinusoidal voltage source, voltage drop VAB(t) across the resistance R is:

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The peak voltage in the output of a half-wave diode rectifier fed with a sinusoidal signal without a filter is 10 V. The DC component of the output voltage is:

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A transistor is used as an amplifier in CB mode with a load resistance of 5 kÎ©. The current gain of the amplifier is 0.98, and the input resistance is 70 Î©. The voltage gain and power gain respectively are:

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The Bohr radius of the fifth electron of phosphorus (atomic number = 15) acting as a dopant in silicon (relative dielectric constant = 12) is:

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For the following circuits PN-junction diodes D1, D2, and D3 are ideal. For the following potential of A and B, the correct increasing order of resistance between A and B will be:

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The circuit contains two diodes, D1 and D2, each with a forward resistance of 50 ohms and infinite backward resistance. If the battery voltage is 6 V, the current through the 100 ohm resistance (in amperes) is:

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Find VAB:

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A diode is connected to 220 V (rms) AC in series with a capacitor. The voltage across the capacitor is:

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A potential difference of 2V is applied between the opposite faces of a Ge crystal plate of area 1 cmÂ² and thickness 0.5 mm. If the concentration of electrons in Ge is $2 imes 10^{19}/m^3$ and mobilities of electrons and holes are $0.36 m^2/volt-sec$ and $0.14 m^2/volt-sec$ respectively, then the current flowing through the plate will be:

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The contribution in the total current flowing through a semiconductor due to electrons and holes are $\frac{3}{4}$ and $\frac{1}{4}$ respectively. If the drift velocity of electrons is twice that of holes at this temperature, then the ratio of concentration of electrons and holes is:

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Ge and Si diodes conduct at 0.3 V and 0.7 V respectively. In the following figure, if Ge diode connection is reversed, the value of V0 changes by:

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In the circuit shown, the maximum output voltage V0 is:

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In the following circuit, find I1 and I2:

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For the transistor circuit shown below, if Î² = 100, voltage drop between emitter and base is 0.7 V, then value of VCE will be:

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In NPN transistor, if 10 electrons enter in the emitter region in $10^{-6}$ sec and 2% electrons are lost in the base region, then collector current and current amplification factor (Î²) respectively are:

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The following configuration of gate is equivalent to:

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The figure gives a system of logic gates. To produce a high output (1) at R, we must have:

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The combination of gates shown below produces:

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The diagram of a logic circuit is given below. The output F of the circuit is represented by:

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## Study Notes

### Diodes and Electronics

#### P-Type Semiconductor

- Made by doping Indium atoms into silicon specimen
- Average of one Indium atom per 5 x 10^7 silicon atoms
- Number density of atoms in silicon specimen: 5 x 10^28 atoms/m^3
- Number of acceptor atoms in silicon per cubic centimeter: 1.0 x 10^17 atoms/cm^3

#### Probability of Electrons in Conduction Band

- Decreases exponentially with increasing band gap
- Depends on temperature and band gap

#### Ionisation Energy of Donor in Silicon

- Typically 0.1 eV

#### PN-Junction Diode

- Reverse saturation current: 10^-5 A at 27Â°C
- Forward current: increases exponentially with voltage

#### Insulators, Semiconductors, and Metals

- Insulator at 0 K: zero current
- Semiconductor at 0 K: zero current
- Metal at 0 K: finite current
- P-N diode at 300 K: finite current if reverse biased

#### Diode Circuits

- Diode with zero forward resistance and infinite reverse resistance
- Current supplied by battery depends on diode configuration
- Voltage drop across diode depends on current and resistance

#### Transistor Amplifier

- Current gain depends on load impedance and current amplification factor (Î²)
- Output voltage depends on input voltage and Î²

#### Semiconductor Resistance

- Depends on concentrations of electrons and holes
- Depends on mobilities of electrons and holes

#### Diode Rectification

- Half-wave rectification: output voltage is half of input voltage
- Full-wave rectification: output voltage is same as input voltage
- Peak voltage in output: depends on input voltage and rectification type

#### Transistor Characteristics

- CB mode: voltage gain and power gain depend on load resistance and Î²
- Current gain: depends on input resistance and Î²

#### Bohr Radius

- Depends on atomic number and relative dielectric constant
- Typically 10.6 Ã… for phosphorus in silicon

#### Diode Circuits (continued)

- Dependence of resistance on diode configuration
- Diode voltage and current relationships

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## Description

Quiz on semiconductor physics for JEE HOTS, covering topics like doping and acceptor atoms in silicon specimens.