Saturday, June 29, 2013

Electronic Devices: Part-3 Objective Questions

[1] In order for a BJT to conduct under the conditions of no signal input, the bias must be
(a) In the reverse direction at the E-B junction, sufficient to cause forward breakover.
(b) In the reverse direction at the E-B junction, but not sufficient to cause avalanche effect.
(c) Such that the application of a signal would cause the transistor to go into a state of cutoff.
(d) Such that the application of a signal would cause the transistor to go into a state of saturation.
(e) Such that the application of a signal would cause the transistor to become nonlinear.

Answer: A
[2] The high input impedance of a MOSFET makes this type of device ideal for use in
(a) Weak-signal amplifiers
(b) High-power oscillators
(c) High-current rectifiers
(d) Antenna tuning networks
(e) Graphic equalizers

Answer: A
[3] The drain of a JFET is the analog of the
(a) Plate of a vacuum tube
(b) Emitter of a BJT
(c) Cathode of diode
(d) Positive electrode in a solar cell
(e) Substrate of a MOSFET

Answer: A
[4] One of the technical limitations of capacitive proximity sensors is the fact that they
(a) Are not very sensitive to objects that are poor electrical conductors.
(b) Are insensitive to objects that reflect light.
(c) Are insensitive to metallic objects.
(d) Cannot be used with oscillators
(e) Require extreme voltages in order to function properly

Answer: A
[5] The power factor in an ac circuit is defined as
(a) The actual power divided by the maximum power the circuit can handle.
(b) The ratio of the real power to the imaginary power.
(c) The ratio of the apparent power to the true power.
(d) The ratio of the true power to the apparent power.
(e) The ratio of the imaginary power to the apparent power.

Answer: D
[6] The amount of current that a silicon photodiode can deliver in direct sunlight depends on
(a) The forward breakover voltage.
(b) The thickness of the substrate.
(c) The surface area of the P-N junction.
(d) The applied voltage.
(e) The reverse bias.

Answer: C
[7] In an amplifier that employs a P-Channel JFET, the device can usually be replaced with an N-channel JFET having similar specifications, provided that
(a) All the resistors are reversed in polarity for the circuit in question
(b) The power supply polarity is reversed for the circuit in question
(c) The drain, rather than the source, is placed at signal ground
(d) The output is taken from the source, rather than from the drain.

Answer: B
[8] Secondary breakdown occurs in
(a) MOSFET but not in BJT
(b) Both MOSFET and BJT
(c) BJT but not in MOSFET
(d) None of these

Answer: C
[9] In a transistor
(a)  β =  α/ (α +1)
(b)  β =  α/ (1- α)
(c)  α =  β/ (β-1)
(d)  α = (β+1)/β

Answer: C
[10] The interbase resistance of a UJT is
(a) Less than forward biased PN diode
(b) Higher than a FET
(c) Of the order of 1K an less
(d) In the range of 5K to 10K

Answer: D
[11] The VI characteristics of emitter of a UJT is
(a) Similar to CE with a linear and saturation region
(b) similar to FET with a linear and saturation region
(c) Similar to tunnel diode in some respects
(d) Linear between the peak point and vally point

Answer: C
[12] An UJT used for triggering as SCR has the supply voltage VBB = 25V. The intrinsic stand off ratio n = 0.75. The UJT will conduct when the bias voltage VE is
(a)  25V
(b)  >=18.75V
(c)  33.3V
(d)  >=19.35V

Answer: D
[13] The Oscillator which is not dependent on phase shift is
(a) Wien Bridge
(b) Clapp
(c) Relaxation
(d) Crystal

Answer: C
[14] For an UJT to function, the load line must extend
(a) from saturation region to ohmic region
(b) from saturation to peak value of emitter voltage
(c) from valley point to peak point
(d) within valley and peak points in the negative resistance region

Answer: D

Solution Hint:
[12] VE  = η.VBB + 0.6   =0.75 x 25 +0.6  =19.35
11:30 PM

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