Quiz: Electrical Engineering
Exam: SSC JE
Topic: Measurement and measuring instrument
Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute
Q1. If an ammeter is connected, like a voltmeter, across the load circuit,
(a)The reading will be low
(b)Almost no current will flow through the meter
(c)The loading effect will be low
(d)An inadmissibly high current will flow through the meter and meter may burn out
Q2. Moving iron and PMMC instruments can be distinguished from each other by looking at
Q3. If a voltmeter is connected, like an ammeter, in series with the load,
(a)Almost no current will flow in the circuit
(b)The measurement reading will be too high
(c)The meter will burn out
(d)An inadmissibly high current will flow
Q4. The internal resistance of a milli-ammeter must be very low for
(d)minimum effect on the current in the circuit.
Q5. The inductance of a certain moving iron ammeter is expressed as L = 2+5θ-θ2 µH. The control spring torque is 2 × 10-6 Nm/radian. Find the deflection in radians for a current of 2A
Q6. If the instrument is to have a wide range, the instrument should have
(a) Linear scale
(b) Square-law scale
(c) Exponential scale
(d) Logarithmic scale
Q7. Which of the following meters has a linear scale?
(a) Thermocouple meter
(b) Moving iron meter
(c) Hot wore meter
(d) Moving coil meter
Q8. No eddy current and hysteresis losses occur in
(a) Electrostatic instruments
(b) PMMC instruments
(c) Moving iron instruments
(d) Electro-dynamo meter instruments
Q9. The deflection expression θ ∝ V^2 dc/dθ, applies to the:
(a)Moving iron type instrument
(b)Electrodynamic type instrument
(c)Electrostatic type instrument
(d)Induction type instrument
Q10. A, 0-150V voltmeter has a guaranteed accuracy of 1 per cent full-scale reading. The voltage measured by this instrument is 83V. The limiting error in per cent will be—
(d)None of these
Sol. current coil has very small resistance. When it is connected in place of the voltage coil, then the whole current will flow through it and will cause damage to the current coil.
Sol. A PMMC instruments has linear scale whereas moving iron instrument has non-linear /non-uniform scale.
Sol. Voltmeter has very high resistance to ensure that its connection do not alter flow of current in the circuit. Now if it is connected in series then no current will be there in the circuit due to its high resistance. Hence it is connected in parallel to the load across which potential difference is to be measured.
Sol. A high value of internal resistance will vary the current considerably in a milli-ammeter as the current is in milli range. So, the internal resistance of a milli-ammeter must be very low.
Sol. The deflecting torque of a moving iron instrument (T) = 1/2 I^2 dL/dӨ
I = 2A; T = 2 × 10-6 Nm/radian; dL/dθ = 5-2θ µH;
So, 5-2θ = 1; θ = 2.
If the scale is directly proportional to the quantity being measured, then it follows the uniform law
If the scale is directly proportional to the square of the quantity being measured, then it follows the square law
If an instrument has a cramped scale for larger values, then it follows logarithmic law; In this case, the instrument instruments will have a wide range
Sol. Moving coil meter
Sol. No eddy current and hysteresis losses occur in Electrostatic instruments.
Sol. The deflection expression θ ∝ v2 dc/dθ, applies to the electrostatic instruments.
Sol. Given voltmeter range 0–150V
measured value = 83V
The magnitude of the limiting error
= 0·01 × 150V = 1·5V
The percentage error at a meter indication of 83V will be
= 1.5/83 × 100 = 1.81 %