Multiple choice question for engineering
1. Bridge balance equation for magnitude is given by the relation
a) Z1 Z4 = Z2 Z3
b) Z1 Z2 = Z3 Z4
c) Z2 Z4 = Z1 Z3
d) Z1 Z3 = Z2 Z4
Answer: a [Reason:] In an AC bridge, the balance condition for magnitude is given by the equation
Z1 Z4 = Z2 Z3 where, Z1, Z2, Z3 and Z4 are the impedance arms of the AC bridge circuit.
2. Angular balance equation is given by the relation
a) θ1 × θ4 =θ2 × θ3
b) θ1 + θ4 =θ2 + θ3
c) θ2 + θ4 =θ1 + θ3
d) θ2 × θ4 =θ1 × θ3
Answer: b [Reason:] The angular balance condition in an AC bridge is given by the relation
θ1 + θ4 = θ2 + θ3 Where,
θ1, θ2, θ3 and θ4 are the phase angles of the impedances Z1, Z2, Z3 and Z4.
3. Bridge must be balanced for ________
c) magnitude and angle
Answer: c [Reason:] The ratio arms consist of impedances which have magnitude as well as phase. In an AC bridge, balance condition implies magnitude balance as well as angular balance.
4. Phase angle is based on _______
Answer: d [Reason:] The four ratio arms comprise of impedances which consist of not only magnitude but some phase as well. Value of the phase angles are based on the component of individual impedances.
5. For inductive impedances, the phase angle is _______
Answer: a [Reason:] The current through an inductor does not increase instantaneously. For inductive impedances, the voltage leads the current and as a result the phase angle is positive.
6. For capacitive impedances, the phase angle is _______
Answer: b [Reason:] The voltage across a capacitor does not rise instantaneously. For capacitive impedances, the current leads the voltage and as a result the phase angle is negative.
7. Bridge balance equation for magnitude in terms of admittances is given by the relation.
a) Y1Y3 = Y2Y4
b) Y1Y2 = Y3Y4
c)Y1Y4 = Y2Y3
d) Y1 Y3 = Y2 Y4
Answer: c [Reason:] Admittance is the reciprocal of impedance. The balance condition for magnitude is given by the equation
8. When bridge is balanced?
a) no voltage drop across the circuit
b) power dissipation is high
c) temperature of the circuit is high
d) no current flows
Answer: d [Reason:] At balance condition, no current flows through the headphones present in the AC bridge circuit. As a result the detector indicates null deflection at balance condition.
1. Capacitance of a parallel plate capacitor is ________
a) C = A∈⁄d
b) C = ∈⁄d
c) C = A⁄d
d) C = A
Answer: a [Reason:] 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 ________
Answer: b [Reason:] 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 ________
Answer: c [Reason:] The capacitance of a cylindrical capacitor is given by the relation
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
Answer: d [Reason:] 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.
Answer: a [Reason:] 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.
6. Capacitive transducer displays ________
a) linear behaviour
b) non-linear behaviour
c) exponential behaviour
d) tangential behaviour
Answer: b [Reason:] 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 ________
Answer: c [Reason:] 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
c) directly proportional
d) inversely proportional
Answer: d [Reason:] 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
c) proportional to square
d) inversely proportional
Answer: a [Reason:] 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
Answer: b [Reason:] In a composite capacitance, there is more than one dielectric medium. The capacitance is given by
are the thicknesses
are the permittivities of the three different media.
1. Electron gun section ________
a) provides sharp beam
b) provides poorly focussed beam
c) doesn’t provide any beam
d) provides electrons only
Answer: a [Reason:] In a cathode ray tube, the electron gun section gives a sharply focussed beam of electrons. They are focussed towards the fluorescent coated screen.
2. Control grid is given ________
a) positive voltage
b) negative voltage
c) neutral voltage
d) zero voltage
Answer: b [Reason:] Grid controls the amount of electrons falling on the fluorescent screen of a cathode ray tube. Cathode ray tube is provided with a negative voltage with respect to the cathode as a reference.
3. What determines light intensity in a CRT?
c) momentum of electrons
d) fluorescent screen
Answer: c [Reason:] Momentum of the electrons gives the intensity or brightness of the light emitted from the fluorescent screen due to electron bombardment. It is given as the product of the no of electrons and their speed.
4. Effect of negative voltage to the grid is ________
a) no force
b) a gravitational force
c) an attractive force
d) a repulsive force
Answer: d [Reason:] Since the electron is negatively charged, application of a negative voltage to the control grid produces a repulsive force.
5. Electron beam diverges.
Answer: a [Reason:] Similar charges on electrons lead to a repulsion. As a result the electron beam diverges as it contains many electrons. Electrostatic force is applied between the focussing anodes in order to compensate the repulsive force.
6. Focusing and accelerating anodes are ________
Answer: b [Reason:] Focussing and accelerating anodes in a cathode ray tube are essentially cylindrical in nature. Each electrode has a small opening at the centre with a co-axial tubular axis.
7. Deflection system of a CRT consists of ________
a) 4 plates
b) 6 plates
c) 2 plates
d) 8 plates
Answer: c [Reason:] Cathode ray tube consists of two sets of plates which are parallel in nature. They are referred to as horizontal and vertical deflection plates. One of the plates is set to ground potential.
8. Horizontal deflection is given by ________
a) x = Kx
b) x = Vx
c) x = 1
d) x = Kx Vx
Answer: d [Reason:] In a cathode ray tube the horizontal deflection is given by,
x = Kx Vx where, Kx is the constant of proportionality
x is the horizontal deflection
Vx is the horizontal deflecting voltage.
9. Vertical deflection is given by ________
a) y = Ky Vy
b) y = Ky
c) x = 1
d) y = Vy
Answer: a [Reason:] In a cathode ray tube the vertical deflection is given by,
y = Ky Vy where, Ky is the constant of proportionality
y is the vertical deflection
Vy is the vertical deflecting voltage.
1. Accuracy is defined as the closeness that a reading approaches with respect to a standard value.
Answer: a [Reason:] Accuracy in the measurement of a quantity is defined as the closeness that a reading approaches when it measured with a standard value.
2. The output of a transducer must ___________
a) be different at different environment conditions
b) be same at all environment conditions
c) be same at some environment conditions
d) be zero always
Answer: b [Reason:] Output of a transducer must be the same under various environmental conditions when same input is applied to it.
3. The output of a transducer must be __________
Answer: c [Reason:] Output of a transducer is usually high so that it can be easily measured and processed. The transducer output is generally higher than noise. As a result most of the application makes use of digital outputs.
4. The size of a transducer must be __________
Answer: d [Reason:] A transducer generally has a small size and shape. It occupies minimum volume and has a minimum weight. As a result the system being measured will become compact.
5. A transducer must be __________
a) quick in response
b) slow in response
c) medium in response
d) very slow in response
Answer: a [Reason:] The transducer is generally fast in response. Speed of response basically tells the time taken by the transducer to produce the output in a fast and efficient manner.
6. The output of a transducer must __________
a) be less reliable
b) be highly reliable
c) not be reliable
d) be of medium reliability
Answer: b [Reason:] Output of a transducer is generally high in reliability. Changes in the environment conditions should not affect the output of a transducer.
7. The range of a transducer is __________
Answer: c [Reason:] A transducer has a large range of operation. The operating range is set wide so that it is useful for a wide range of operating frequencies.
8. The transducer output is __________
b) unit step
Answer: d [Reason:] Transducer output varies linearly with the input quantity that is being measured. A transducer must have a linear input vs output characteristic response.
9. The sensitivity of an electrical transducer is obtained by dividing the electrical output with respect to unit change in the physical quantity.
Answer: a [Reason:] Sensitivity of an electrical transducer is defined as the ratio of the electrical output to a unit change in the value of a physical quantity such as temperature, pressure etc.
1. Increasing secondary burden
a) increases Is
b) decreases Is
c) keeps Is constant
d) decreases Ip
Answer: a [Reason:] When the secondary burden of a potential transformer increases, it leads to an increase in the secondary current. As a result the primary current also increases.
2. For a given Vp the Vs
c) remains constant
d) depends on the supply
Answer: b [Reason:] For a particular value of primary voltage Vp, the value of the secondary voltage Vs decreases. This leads to a decrease in the actual ratio.
3. What is effect of the secondary burden on the ratio error?
a) ratio error is constant with secondary burden
b) ratio error decreases with secondary burden
c) ratio error increases with secondary burden
d) depends on the supply voltage
Answer: c [Reason:] As the secondary burden is increased, the ratio error also increases and becomes more negative. Ratio error varies linearly with respect to the change in the secondary burden.
4. Vp is leading in phase, while Vs is lagging in phase.
Answer: a [Reason:] As the secondary burden is increased, winding voltage drop increases. Voltage Vp is leading in phase while Vs is lagging in phase. As a result the phase angle increases with the secondary burden.
5. What is the effect of p.f. on secondary burden?
a) Ip shifts towards Io
b) Ip deviates from Io
c) Ip is independent of Io
d) Ip and Io cancel eachother
Answer: a [Reason:] When the power factor of the secondary burden is reduced, Ip shifts towards Io. Voltages Vp and Vs come closer to Ep and Es.
6. How is the transformation ratio dependent on the secondary burden?
c) remains constant
d) depends on the supply
Answer: b [Reason:] As the primary voltage Vp is constant, the induced primary e.m.f Ep is reduced. Similarly the secondary voltage Vs is reduced with respect to Es. As a result the transformation ratio increases.
7. Decrease in p.f. makes Vs to lead Vp.
Answer: a [Reason:] As the power factor is decreased, Vs leads in phase while Vp decreases in phase. Thus the phase angle reduces with the decrease in power factor (lagging).
8. At constant voltage how is frequency affected by flux?
a) decreases with increase in flux
b) increases with decrease in flux
c) remains constant
d) depends on the current
Answer: b [Reason:] When frequency is increased at a constant voltage, the flux decreases. Voltage ratio decreases as the magnetizing and iron loss components of current are reduced.