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Right choice is (a) is AFFECTED by light

For explanation I would SAY: The reverse LEAKAGE CURRENT in a transistor is directly proportional to the intensity of light. It increases with the INCREASE in light intensity.

Correct option is (a) True

The best explanation: The optocoupler consists of a phototransistor and an infrared EMITTING DIODE. Wavelength of the emitting and receiving diodes MUST be MATCHED in ORDER to get a proper output.

Right OPTION is (c) electron hole pairs are formed

For explanation: Upon illumination of an open circuited PN junction, electron hole pairs are generated. A small voltage appears across the junction and as a result it ACTS as a voltae source.

The CORRECT answer is (B) thin layer of semiconductor

For explanation I would SAY: Photoconductors comprise of a thin layer of semiconductor. Photoconductors not consisting of a junction are known as junction less detectors.

The correct choice is (d) cesium-antimony

To ELABORATE: Cesium-antimony is the most commonly USED photoemissive material. The photoemissive material is housed in a glass tube. Photoemissive DEVICES are ALSO called as phototubes.

Correct OPTION is (a) True

The explanation: Phototubes are quick in RESPONSE to light. Phototubes are USED in applications which require light PULSES of very short durations to be OBSERVED.

Correct option is (c) due to change in resistance

The explanation is: A photoconductive transducer produces an OUTPUT due to a change in the resistance. ELECTRICAL output is produced due to a VARIATION in the TEMPERATURE.

The correct option is (a) optoelectric devices

Explanation: EMISSION and ABSORPTION of OPTICAL radiations are CARRIED out by making USE of optoelectric devices.

Right choice is (b) False

Explanation: A MICROPHONE is used to convert the pressure induced in the FORM of sound WAVES into electric signal. The electrical signal is then AMPLIFIED to produce louder sound.

The correct choice is (a) True

To elaborate: CIGARETTES use piezoelectric transducers as a source of ignition. They are ALSO used in the measurement of SONAR, MICROPHONE, pressure, displacement and force.

The correct CHOICE is (b) LIGHTING a gas STOVE

Explanation: A piezoelectric lighter is used for lighting a gas based stove in KITCHEN applications. The pressure induced on the piezoelectric sensor creates an electric signal LEADING to a spark.

The CORRECT option is (C) high sensitivity

To explain: The sensitivity is high in a piezoelectric transducer. A piezoelectric transducer can be used as a SENSOR. It can also be used in an accelerometer DUE to its good FREQUENCY response.

Right choice is (B) dissolve in water

Explanation: A piezoelectric crystal dissolves in water. It is fully SOLUBLE in water. When the TEMPERATURE is humid, the piezoelectric CRYSTALS gets dissolved in water.

Correct choice is (c) high voltage

Explanation: Piezoelectric crystals can be used SPARK IGNITION engines. They are also used in electrostatic dust filters and PRODUCE high voltage at low current.

Right option is (d) quartz crystal

To ELABORATE: A piezoelectric TRANSDUCER consists of a quartz crystal. It comprises of silicon and OXYGEN arranged in a crystal structure of SIO2.

Correct CHOICE is (a) non-electrical quantities

The BEST I can explain: A piezoelectric transducer is used for measuring non-electrical quantities such as VIBRATION, acceleration, pressure and the intensity of SOUND.

The correct option is (d) WIRE must be heavy

To explain I would SAY: Higher temperatures can be measured USING a thermocouple by making the wire heavy. Increase in size of the wire affects the RESPONSE time of the thermocouple.

Correct choice is (C) platinum

For EXPLANATION: Platinum is the most suitable material for constructing thermocouples. It has a very high sensitivity. Constantan is the other material (alloy) with a composition of 40 % of Ni and 60 % of CU USED in a thermocouple.

The correct choice is (b) False

Easy explanation: When two DIFFERENT metals are JOINED TOGETHER forming a closed circuit, if the temperatures of the two junctions are different then an electric current FLOWS through the circuit.

The correct choice is (d) series of thermocouples

The explanation: THERMOPILE is a series connection of thermocouples. By making use of thermopiles, a more SENSITIVE ELEMENT is obtained as compared to a SINGLE THERMOCOUPLE.

Correct ANSWER is (b) thermocouple

The best explanation: The most COMMONLY used thermoelectric transducer is a thermocouple. It measures the change in temperature and converts it into an ELECTRICAL SIGNAL.

Right answer is (b) more than ONE DIELECTRIC MEDIUM

The explanation is: In a COMPOSITE capacitance, there is more than one dielectric medium. The capacitance is given by

where, d1, d2 and d3 are the thicknesses

∈1, ∈2and ∈3 are the PERMITTIVITIES of the three different media.

The correct choice is (d) inversely proportional

To explain I would say: When the capacitance is LOW in the range of pico-farads, output IMPEDANCE tends to a high VALUE. This LEADS to LOADING effect.

Right choice is (c) low

Easy explanation: In a capacitive transducer, long leads and CABLES are USED. Due to LOADING effect, frequency RESPONSE is poor and the sensitivity reduces.

Right option is (a) True

The explanation is: A capacitive PRESSURE transducer is based on the principle of distance of separation between the plates of the capacitor. Capacitance of a PARALLEL PLATE capacitor varies when the distance between the two parallel plates changes.

Correct choice is (d) 4 ways

The explanation: CAPACITANCE is varied in four ways. They are as FOLLOWS:

 CHANGE of distance

 Change in dielectric

 Change in common plate area

 USING quartz diaphragms.

The CORRECT CHOICE is (B) capacitance

Explanation: A CAPACITIVE transducer WORKS on the principle of capacitance. The capacitance of a system depends on the dielectric used as well as the properties of a capacitive system.

The correct choice is (a) C = ^A∈⁄d

The BEST explanation: The capacitance of a parallel PLATE capacitor is given by the relation,

C = ^A∈⁄d

where,

A is the AREA of CROSS section of the plates

d is the distance of separation between the plates

∈ is the permittivity of space.

Right choice is (a) True

Easy EXPLANATION: An inductive TRANSDUCER is usually used for the measurement of PHYSICAL quantities such as pressure, force, displacement, POSITION, vibration, velocity, etc.

Right answer is (a) True

The BEST explanation: An EDDY current transducer is a self-generating type of inductive transducer. In an eddy current transducer, OUTPUT depends on the change in the VALUE of the eddy current at the INPUT.

The CORRECT answer is (d) self-inductance

To ELABORATE: Inductive transducer MEASURES the variation in the self-inductance and mutual inductance of an inductive coil. Variation in the inductance is MEASURED as a change in the displacement.

The correct answer is (B) inversely proportional

The explanation is: The self-inductance of an inductor is obtained by making USE of the relation

L = ^N^2⁄S

where, N is the NUMBER of COIL

S is the reluctance of the coil (A/Wb)

We observe from the above equation that the self-inductance of a coil is inversely proportional to its reluctance.

The correct option is (c) 4

Explanation: Based on the self-inductance of an INDUCTIVE COIL, there are FOUR types of inductive transducers available. They are as follows:

i) VARIABLE permeability inductive transducer

ii) Variable reluctance inductive transducer

iii) Eddy current inductive transducer

iv) LINEAR variable differential transducer.

Right answer is (a) permeability

For explanation: The self-inductance of an inductor is obtained by MAKING USE of the relation

L = ^N^2⁄S

where, N is the NUMBER of coil

S is the reluctance of the coil (A/Wb)

As reluctance depends on the permeability, the self-inductance of a coil depends on the permeability.

Correct ANSWER is (d) S = ^1⁄μA

Explanation: The reluctance of an inductance COIL is GIVEN by the relation

S = ^1⁄μA

where, l is the length of the MAGNETIC circuit (m)

a is the area of the magnetic circuit which encloses the FLUX (m^2)

µ is the permeability of the core (H/m).

Right option is (c) L = ^N^2⁄S

The EXPLANATION is: The self-inductance of an inductor is obtained by making use of the relation

L = ^N^2⁄S

where, N is the number of COIL

S is the RELUCTANCE of the coil (A/Wb).

Right answer is (B) self-inductance and coefficient of COUPLING

The explanation: The mutual inductance of a PAIR of coils depends on the self-inductance of the INDIVIDUAL coils and on the coefficient of coupling.

Correct ANSWER is (a) M = k\(\sqrt{L_1 L_2}\)

EASIEST EXPLANATION: The mutual inductance between two coils is given by the relation

M = k\(\sqrt{L_1 L_2}\)

where, k is the COEFFICIENT of coupling

M is the mutual inductance between the coils.