Test: Electrical And Electronic Measurements- 5


10 Questions MCQ Test Mock Test Series for Electrical Engineering (EE) GATE 2020 | Test: Electrical And Electronic Measurements- 5


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QUESTION: 1

For the bridge shown Z1 = 200 ∠20° Ω, Z2 = 150 ∠30° Ω  and Z3 = 300 ∠-30° Ω. What is the value of Zso that the bridge is balanced?

Solution:

At bridge balance condition,
Z1 Z= Z2 Z3
⇒ 200 ∠20° Z4 = 150 ∠30°    300 ∠-30°
⇒ Z4 = 225 ∠-20° Ω

*Answer can only contain numeric values
QUESTION: 2

A simple slide wire potentiometer is used for measurement of current in the circuit. The voltage drop across a standard resistor of 0.6Ω is balanced at 60 cm. The magnitude of current if the standard cell of 4V is balanced at 50 cm is ______ (in A)


Solution:

Standard cell of 4 V is balanced at 50 cm.
The voltage drop across 60 cm 
The working current through the circuit is,

QUESTION: 3

In the bridge circuit shown in figure when then the voltmeter reads
  

Solution:

At bridge balance condition
(2R) (Xc) = (2R) (R)
Given that, 
at this condition, bridge is balanced
Hence the voltmeter reading is 0 V.

*Answer can only contain numeric values
QUESTION: 4

A resistance potentiometer has a total resistance of 4 kΩ and is rated 10W. If the range of potentiometer is 0 to 200 mm. then its sensitivity is _______ (in V/mm)


Solution:

R = 4 kΩ
P = 10 W
We know that.

The potentiometer range is 0 to 200 mm.

QUESTION: 5

A length of cable was tested for insulation resistance using loss of charge method. A capacitance formed by sheath of cable of 300 PF is found to have drop in voltage from 300 V to 100 V in 120 seconds. Calculate the insulation resistance of the cable in MΩ 

Solution:

Given that = C = 300 pF
V1 = 300 V
V2 = 100 V
t = 120 S

*Answer can only contain numeric values
QUESTION: 6

Calculate the value of effective resistance (in Ω) at a supply frequency of 100 Hz. (C= 2 μF)


Solution:

Under balance condition

Separate and equating real and imaginary part.

*Answer can only contain numeric values
QUESTION: 7

Find the excitation frequency (in Hz) in the Ac Bridge shown in figure under balance condition. The circuit component values are given as
R1 = 100 kΩ,
R3 = R4 = 100 kΩ,
C1 = 2 C2 = 10 nF


Solution:

under bridge balance condition,

 

Given that, R3 = R4

(1 + jωR1C1)(1 + jωR2C2) = jωC1R2
1 + jωR1C+ jωR2C− ω2R1R2C1C= jωC1R2
By comparing real parts on both sides,

By comparing imaginary parts on both sides,

QUESTION: 8

The Schering bridge shown in figure has the following constant R1 = 1.5 kΩ, C1 = 0.4 μF, R2 = 3 kΩ and C3 = 0.4 μF at frequency 1 kHz. The dissipation factor is_______

Solution:

Given, R1 = 1.5 kΩ
C1 = 0.4 μF
R2 = 3 kΩ
C3 = 0.4 μF
f = 1 kHz
We know that,

and the unknown capacitance

Dissipation factor

= 2πfCxRx
= 2π × 1 × 103 × 0.2 × 10-6 × 3 × 103
= 3.77 

*Answer can only contain numeric values
QUESTION: 9

The AC bridge is supplied with a source of frequency 5 kHz as shown in the figure. If the bridge is balanced at R1 = 4 R2 and C3 = 20 μF, the value of unknown capacitor Cx is _____ (in μF)


Solution:

At bridge balanced condition,


By comparing imaginary part,

QUESTION: 10

The dc potentiometer shown in the figure has working current of 10 mA with switch S open. Let Rg + R1 = 100Ω. The galvanometer G can only detect currents greater than 10 μA. The maximum percentage error in the measurement of the unknown e.m.f. Ex as calculated from the slider position shown is closest to

Solution:

Given that, when the switch is open.
IW = 10 mA

⇒ Rx = 50 Ω.
Length of Rx = 5m.
Resistance across 3m = 30 Ω
Resistance across 2m = 20 Ω
Voltage across 20 Ω = 20 × 10 × 10-3 = 0.2 V
Errors in the reading are due to Rg and R1.
Error = voltage drop across Rg and R1
= Ig (Rg + R1)
= 10 × 10-6 (100) = 1 mV