Exercise: Measurements And Instrumentation

Questions for: Measurements And Instrumentation

The current through a resistance R is shown in figure. The computed value of power is
A:
400 ± 0.42 W
B:
400 ± 4.6 W
C:
400 ± 8.85 W
D:
400 ± 10.65 W
Answer: C

% error in current is 2% and % error in resistance is 0.2%.

Since P = I2R, % error in power = 2 x 2% + 0.2% = 4.2%.

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In a thermocouple two metal junctions between metals M1 and M2 are kept at temperature T1 and T2. The thermocouple emf is produced because
A:
M1, M2 are similar and T1, T2 are equal
B:
M1, M2 are similar but T1, T2 are unequal
C:
M1, M2 are dissimilar but T1, T2 are equal
D:
M1, M2 are dissimilar but T1, T2 are unequal
Answer: D

The two materials in thermocouple are different and the two junctions are kept at different temperatures.

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A 300 V voltmeter has an accuracy of ± 2% of full scale deflection. When the reading is 222 V, the actual voltage
A:
lies between 217.56 and 226.44 V
B:
lies between 217.4 and 226.6 V
C:
lies between 216 and 228 V
D:
is exact 222 V
Answer: C

Error = ± 6 V. Therefore, the actual value would be between 222 ± 6 V.

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Two voltmeters are each 0-300 V range. Their internal resistances are 10 kΩ and 20 kΩ They are connected is series and a voltage of 400 V is applied. Their readings respectively will be
A:
266.6 and 133.3 V
B:
133.3 and 266.6 V
C:
200 V each
D:
100 and 300 V
Answer: B

The readings will be proportional to their internal resistance,

.

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A moving iron instrument can be used for
A:
dc only
B:
ac only
C:
both dc and ac
D:
dc and high frequency ac
Answer: C

Its deflecting torque ∝ I2. So, it can be used for both d.c. and a.c.

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