# Electrical Measurements Questions and Answers – Capacitive Transducer

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers (MCQs) focuses on “Capacitive Transducer”.

1. Capacitance of a parallel plate capacitor is ________
a) C = A∈d
b) C = d
d) C = A

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.

2. A capacitive transducer works on the principle of ________
a) inductance
b) capacitance
c) resistance
d) reluctance

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.

3. Capacitance of a cylindrical capacitor is given by which of the following relation?
a) C = $$\frac{∈l}{ln⁡(\frac{R}{r})}$$
b) C = $$\frac{2πl}{ln⁡(\frac{R}{r})}$$
c) C = $$\frac{2π∈l}{ln⁡(\frac{R}{r})}$$
d) C = $$\frac{2π∈}{ln⁡(\frac{R}{r})}$$

Explanation: The capacitance of a cylindrical capacitor is given by the relation
C = $$\frac{2π∈l}{ln⁡(\frac{R}{r})}$$
where, l is the length of the cylinder
R is the inner radius of the external cylinder
r is the outer radius of the inner cylinder.

4. Capacitance can be varied in ________
a) 10 ways
b) 6 ways
c) 2 ways
d) 4 ways

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.

5. Capacitive pressure transducer uses distance of separation for sensing the capacitance.
a) True
b) False

Explanation: 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.
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6. Capacitive transducer displays ________
a) linear behaviour
b) non-linear behaviour
c) exponential behaviour
d) tangential behaviour

Explanation: A capacitive transducer displays non-linear behaviour. This is due to stray electric fields. Guard rings are required to eliminate the edge effects and the parasitic electric field effects.

7. Frequency response of capacitive transducers is ________
a) high
b) medium
c) low
d) zero

Explanation: In a capacitive transducer, long leads and cables are used. Due to loading effect, frequency response is poor and the sensitivity reduces.

8. What is the relation between capacitance and output impedance?
a) proportional to square
b) constant
c) directly proportional
d) inversely proportional

Explanation: When the capacitance is low in the range of pico-farads, output impedance tends to a high value. This leads to loading effect.

9. What is the relation between capacitance and input impedance?
a) directly proportional
b) constant
c) proportional to square
d) inversely proportional

Explanation: Capacitive transducer has high input impedance. It also has a good frequency response. The loading effects are minimum.

10. Composite capacitance consists of _________
a) one dielectric medium
b) more than one dielectric medium
c) five dielectric media
d) ten dielectric media

Explanation: 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, ∈2 and ∈3 are the permittivities of the three different media.

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