Electronics and Communication Engineering - Measurements and Instrumentation

16. 

In figure, Z1 = 200∠60° Ω, Z2 = 400∠ - 90° Ω, Z3 = 300∠0°. Then Z4 for bridge to be balanced is

A. 150∠30° Ω
B. 400∠ - 90° Ω
C. 300∠90° Ω
D. 600∠ - 150° Ω

Answer: Option D

Explanation:

.


17. 

In a ballistic galvanometer, a charge of 100 μC gives a first swing of 25°. The charge required to cause first swing of 50° is

A. 200 μC
B. 400 μC
C. 50 μC
D. 25 μC

Answer: Option B

Explanation:

swing is proportional to charge.


18. 

Two resistors R1 = 36 Ω ± 5% and R2 = 75 Ω ± 5% are connected in series. The total resistance is

A. 111 ± 0 Ω
B. 111 ± 2.778 Ω
C. 111 ± 5.55 Ω
D. 111 ± 7.23 Ω

Answer: Option C

Explanation:

Total maximum error ± (1.8 + 3.75) = ± 5.55 Ω.


19. 

Figure shows an RC potentiometer to measure ac voltage. It is desired that V0/Vi should be independent of frequency. The value of C should be

A. 10 μF
B. 11 μF
C. 0.1 μF
D. 0.09 μF

Answer: Option A

Explanation:

Since resistances are in the ratio of 10 : 1, capacitances should be in the ratio of 1 : 10 because XC ∝ 1/C.


20. 

In a strain measuring device using a strain gauge, the output quantity is

A. voltage
B. resistance
C. impedance
D. either (a) or (b)

Answer: Option A

Explanation:

The measurement is done using an unbalanced bridge.