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Instruction: Submit your answer sheet (provided) together with this questionnaire to the office for checking.
Time Element: 4 hours
- The total energy of a revolving electron in an atom can:
A. have any value above zero B. never be positive * C. never be negative D. not be calculated
- An atom is said to be ionized when any one of its orbiting electron:
A. jumps from one orbit to another B. is raised to a higher orbit C. comes to the ground state D. is completely removed *
- The maximum number of electrons which the M-shell of an atom can contain is:
A. 32 C. 18 * B. 8 D. 50
- Electronic distribution of an Si atom is:
A. 2, 10, 2 C. 2, 7, 5 B. 2, 8, 4 * D. 2, 4, 8
- Semiconductor materials have ____ bonds.
A. ionic C. mutual B. covalent * D. metallic
- The maximum number of electrons which the valence shell of an atom can have is:
A. 6 C. 18 B. 8 * D. 2
- Silicon has Z = 14. Its outermost orbit is:
A. partially filled B. half filled * C. completely occupied D. empty
- Major pat of the current in an intrinsic semiconductor is due to:
A. conduction-band electrons * B. valence-band electrons C. holes in the valence band D. thermally-generated electrons
- Conduction electrons have more mobility than holes because they
A. are lighter B. experience collision less frequently C. have negative charge
D. need less energy to move them *
- Doping materials are called impurities because they:
A. decrease the number of charge carriers B. change the chemical properties of semiconductors C. make semiconductors less than 100 percent pure D. alter the crystal structures of the pure semiconductor *
- Current flow in a semiconductor depends on the phenomenon of:
A. drift B. recombination C. doping D. all of the above *
- The process of adding impurities to a pure semiconductor is called _____.
A. mixing C. diffusing B. doping * D. refining
- The most widely used semiconducting material in electronic devices is ____.
A. germanium B. copper C. silicon * D. carbon
- Electron-hole pairs are produced by
A. recombination B. ionization C. thermal energy * D. doping
- Recombination takes place when
A. an electron falls into a hole * B. a positive and a negative ion bond together C. a valence electron becomes a conduction D. a crystal is formed
- When a P-N junction is formed, diffusion current causes
A. mixing of current carries B. forward bias C. reverse bias D. barrier potential *
- The leakage current of a P-N diode is caused by:
A. heat energy * B. barrier potential C. chemical energy D. majority carriers
- Electronic components which are made of semiconductor materials are often called ____ devices.
A. solid-state * B. silicon C. germanium D. intrinsic
- Any voltage that is connected across a P- N junction is called ____ voltage.
A. breakdown B. bias * C. barrier D. reverse
- The area within a semiconductor diode where no mobile current carriers exist when it is formed is called ____ region.
A. depletion * B. potential barrier C. saturation D. space charge
- The depletion region of a semiconductor diode is due to:
A. reverse biasing B. forward biasing C. crystal doping D. migration of mobile charge carriers *
- If an intrinsic semiconductor is doped with a very small amount of boron, then in the extrinsic semiconductor so formed, the number of electrons and holes will:
A. decrease B. increase C. increase and decrease respectively D. decrease and increase respectively *
- Two initially identical samples A and B of pure germanium are doped with donors to concentrations of 1 x 20^20 and 3 x 10^20 respectively. If the hole concentration in A is 9 x 10^12 , then the hole concentration in B at the same temperature will be:
A. 3 x 10^12 m-3^ * B. 11 x 10^12 m- C. 7 x 10^12 m- D. 27 x 10^12 m-
- Hall effect is observed in a specimen when it (metal or a semiconductor) is carrying current electric field inside the specimen will be in: A. a direction normal to both current and magnetic field * B. the direction of current C. a direction antiparallel to the magnetic field D. an arbitrary direction depending upon the conductivity of the specimen
ASSIGNMENT 2 - ELECTRONICS ENGINEERING
- Mobilities of electrons and holes in a sample of intrinsic germanium at room temperature are 0.36 m^2 /V-s and 0. m^3 /V-s respectively. If the electron and hole densities are each equal to 2.5 x 10^19 per m^3 , calculate the conductivity in S/m.
A. 4. B. 3. C. 2.12 * D. 1.
- A germanium diode draws 40 mA with a forward bias of 0.25 V. The junction is at room temperature of 293oK. Calculate the reverse saturation current of the diode.
A. 1.82 μA * B. 1.24 μA C. 2.13 μA D. 2.73 μA
- For a silicon diode, the value of the forward bias voltage typically
A. must be greater than 0.3V B. must be greater than 0.7V * C. depends on the width of the depletion region D. depends on the concentration of majority carriers
- When forward bias, a diode
A. blocks current B. conducts current * C. has a high resistance D. drops a large voltage
- The term bias means
A. the ratio of majority carriers to minority carriers B. the amount of current across the P-N junction C. a dc voltage applied across the P-N junction to control its operation * D. none of the above
- To forward-bias a P-N junction, diode,
A. an external voltage is applied that is positive at the anode and negative at the cathode B. an external voltage is applied that is negative at the anode and positive at the cathode C. an external voltage is applied that is positive at the P-region and negative at the N-region D. A and C above *
- When a P-N junction is forward-biased
A. the only current is the hole current B. the only current is the electron current C. the only currents produced by majority carriers D. the current is produced by both holes and electrons *
- A P-N junction diode’s dynamic conductance is directly proportional to
A. the applied voltage B. the temperature C. the current * D. the thermal voltage
- The junction capacitance of a linearly graded junction varies with the applied reverse bias VR as
A. VR- B. VR-1/ C. VR-1/3^ * D. VR1/
- The diffusion capacitance of a forward biased P+^ N (P+^ indicates heavily doped P- region) junction diode with a steady current I depends on:
A. width of the depletion region B. mean life-term of holes C. mean life-term of electrons * D. junction area
- The width of depletion layer of a P-N junction
A. decreases with light doping B. increases with heavy doping C. is independent of applied voltage D. is increased under reverse bias *
- At room temperature of 25oC, the barrier potential for silicon is 0.7V. Its value at 125 oC is ____V.
A. 0. B. 0. C. 0.9 * D. 0.
- Junction breakdown occurs
A. under high temperature condition B. with forward bias C. under reverse bias * D. because of manufacturing defect
- Avalanche breakdown is primarily dependent on the phenomenon of
A. collision * B. ionization C. doping D. recombination
- Reverse current in a silicon junction nearly doubles for every ____oC rise in temperature.
A. 10 B. 6 * C. 2 D. 5
- Without a dc source, a clipper acts like a
A. rectifier *
B. demodulator C. clamper D. chopper
- The primary function of a clamper circuit is to
A. suppress variations in signal voltage B. raise positive half-cycle of the signal C. lower negative half-cycle of the signal D. introduce a dc level into an ac signal *
- What is the color of light emitted by LED if the material used is gallium-arsenide- phosphide (GaAsP)?
A. Infrared radiation B. Blue C. Green D. Red or yellow (amber) *
- Silicon is preferred for manufacturing Zener diodes because it
A. is relatively cheap B. needs lower doping level C. has higher temperature and current capacity * D. has lower breakdown voltage
- When used in a circuit, a Zener diode is always
A. forward-biased B. connected in series C. troubled by overheating D. reverse-biased *
- The main reason why electrons can tunnel through a P-N junction is that
A. they have high energy B. barrier potential is very low C. depletion layer is extremely thin * D. impurity level is low
- The IP/IV ratio of a tunnel diode is of primary importance in
A. determining tunneling speed of electrons B. the design of an oscillator C. amplifier designing D. computer applications *
- Mark the INCORRECT statement. A varactor diode
A. has variable capacitance B. utilizes transition capacitance of a junction C. has always a uniform doping profile * D. is often used as an automatic frequency control device
- The microwave device used as an oscillator within the frequency ragne 10- 1000 GHz is ____ diode.
A. Schottky B. IMPATT *
B. photodiode C. LED D. phototransistor
- Optical couplers are designed to ____, one circuit from another.
A. control C. disconnect B. isolate * D. protect
- The main purpose of using optical isolators is to provide protection to devices from
A. high-voltage transients B. surge voltages C. low-level noise D. all of the above *
- A LED emits visible light when its
A. P-N junction is reverse-biased B. depletion region widens C. holes and electrons recombine * D. P-N junction becomes hot
- In LED, light is emitted because
A. recombination of charge carriers takes place * B. diode gets heated up C. light falling on the diode gets amplified D. light gets reflected due to lens action
- GaAs, LEDs emit radiation in the
A. ultraviolet region B. violet-blue green range of the visible region C. visible region D. infrared region *
- Phototransistors respond much like a conventional transistor except that, in their cases, light energy is used to _____.
A. alter leakage current B. change base voltage C. switch it ON * D. alter emitter current
- The emitter of a transistor is generally doped the heaviest because it
A. has to dissipate maximum power * B. has to supply the charge carriers C. is the first region of the transistor D. must possess low resistance
- For current working of an NPN bipolar junction transistor, the different electrodes should have the following polarities with respect to emitter.
A. collector + ve, base - ve B. collector – ve, base + ve C. collector – ve, base - ve D. collector + ve, base + ve *
- In a properly-biased NPN transistor, most of the electrons from the emitter
A. recombine with holes in the base B. recombine in the emitter itself C. pass through the base to the collector * D. are stopped by the junction barrier
- In a junction transistor, the collector cut off current ICBO reduces considerably by doping the
A. emitter with high level of impurity B. emitter with low level of impurity C. collector with high level of impurity D. collector with low level of impurity *
- In a transistor amplifier, the reverse saturation current ICO
A. doubles for every 10oC rise in temperature * B. doubles for every 1oC rise in temperature C. increases linearly with the temperature D. doubles for every 5oC in temperature
- In the case of a bipolar transistor, α is
A. positive and > 1 B. positive and < 1 C. negative and > 1 D. negative and <1 *
- The EBJ of a given transistor is forward- biased and its CBJ reverse-biased. If the base current is increased, then its
A. IC will decrease B. VCE will decrease C. VCE will increase D. IC will increase *
- The collector characteristics of a CE- connected transistor may be used to find its
A. input resistance B. base current C. output resistance * D. voltage gain
- When a transistor is fully switched ON, it is said to be
A. shorted C. open B. saturated * D. cut-off
- If a change in base current does not change the collector current, the transistor amplifier is said to be
A. saturated * C. critical B. cut-off D. complemented
- When an NPN transistor is saturated, its VCE
A. is zero and IC is zero B. is low and IC is high * C. equals VCC and IC is zero D. equals VCC and IC is high
- When an NPN transistor is cut-off, its VCC
A. equals VCC and IC is high B. equals VCC and IC is zero * C. is low and IC is high D. is high and IC is low
- If, in a bipolar junction transistor, IB = 100 μA and IC = 10 mA, in what range does the value of its beta lie?
A. 0.1 to 1. B. 10.1 to 100 C. 1.01 to 10 * D. 100.1 to 1000
- In a BJT, largest current flow occurs
A. in the emitter * B. in the base C. through CB junction D. in the collector
- In a properly-connected BJT, an increase in base current causes increase in
A. IC only B. both IC and IE * C. IE only D. leakage current
- When a BJT operates in cut-off
A. VCE = 0 B. VCE = VCC * C. VCE has negative value D. IC is maximum
- When a BJT is in saturation
A. IC = 0 B. IB controls IC C. VCE = 0 * D. VCE has positive value
- A transistor is operated as a non-saturated switch to eliminate
A. storage time * C. turn-off time B. turn-on time D. delay time
- Early-effect in BJT refers to
A. avalanche breakdown B. thermal breakdown C. base narrowing * D. zener breakdown
- A dc chopper has ON time of 30 μs and OFF time of 10 μs. Calculate the chopping frequency.
A. 20 kHz C. 25 kHz * B. 50 kHz D. 30 kHz
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