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Electronics and Communication Engineering - Measurements and Instrumentation

Exercise : Measurements and Instrumentation - Section 1
31.
A full wave rectifier type meter is used to measure the wave shape shown in figure. The voltmeter is calibrated to read rms value of sine wave. The reading of voltmeter will be
100 V
111 V
Answer: Option
Explanation:

Peak value of sine wave = 100 x 1.11 = 111 V.

32.
A moving coil instrument has a resistance of 0.5 Ω and a full scale deflection of 0.1 A. To convert it into an ammeter of 0-10 A the shunt resistance should be
0.004 Ω
0.005 Ω
0.05 Ω
0.1 Ω
Answer: Option
Explanation:

.

33.
Potentiometer method of dc voltage measurement is more accurate than direct measurement using a voltmeter because
it loads the circuit to maximum extent
it loads the circuit moderately
it does not load the circuit at all
it uses centre zero galvanometer instead of Voltmeters
Answer: Option
Explanation:

Since the circuit is not loaded, the accurate value of dc voltage is measured.

34.

Assertion (A): A hot wire ammeter has a cramped scale.

Reason (R): The heat is proportional to square of current.

Both A and R are true and R is correct explanation of A
Both A and R are true but R is not correct explanation of A
A is true R is false
A is false R is true
Answer: Option
Explanation:

Since heating ∝ I2, scale is cramped.

35.
Which of the following is true about an impulse voltage?
It is a unidirectional voltage
Chopped impulse flashover does not occur
Time taken to rise is equal to time taken to fall
RMS value is always less than 50% of average value
Answer: Option
Explanation:

Impulse is unidirectional (either positive or negative).

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