24 + Interview Questions in ELECTRICAL-INSTRUMENTS IN GENERAL AWARENESS Page 1 InterviewSolution

1.	A galvanometer with a coil of resistance `10.0Omega` shows full scale deflection for a current of 50mA. How will you convert the galvanometer into (i). An ammeter of range 0 to 0.5 A and (ii). A voltmeter of range 0 to 5V?
Answer» Correct Answer - `10//9Omega` in parallel `90Omega` in series

Discussion

2.	A galvanometer of resistanece `40Omega` gives a deflection of 5 divisions per mA. There are 50 divisions on the scale. Calculate the maximum current that can pass through it when a shunt resistance of `2Omega` is connected.
Answer» Correct Answer - 210mA

Discussion

3.	A galvanometer has a resistance of `100Omega`. A difference of potential of 1.0 V between its terminals gives a full scale deflection. Calculate the shunt resistance which will enable the instrument to read upto 2A.
Answer» Correct Answer - `0.5Omega`

Discussion

4.	When a galvanometer having 20 divisions scale and `50Omega` resistance is connected in series to a cell of emf `1.5V` through a resistance of `100Omega`, its shows full scale deflection. Find the figure of merit of the galvanometer.
Answer» Correct Answer - 0.5mA/div

Discussion

5.	A certain length of a uniform wire of resistance `12Omega` is bent into a circle and two points, a quarter of circumference apart, are connected to a battery of emf 4 V and internal resistance `1Omega`. Find the current in the different parts of the circuit.
Answer» Correct Answer - `(12)/(13)A,(4)/(13)A`

Discussion

6.	A potentiometer is being used to determine the internal resistance of a primary cell. The balance point for the cell in an open circuit is at 76.3 cm. when the cell sends a current in a resistor of `9.5Omega`, the balance point shifts to 64.8cm. Find the internal resistance of the cell.
Answer» Correct Answer - `1.68Omega`

Discussion

7.	With a certain cell, the balance point is obtained at 60 cm from the zero end of the potentiometer wire. With another cell whose emf differs from that of the first cell by 0.1 V, the balance point is obtained at 50 cm mark. Calculate the emf of the two cells.
Answer» Correct Answer - 1.2 V, 1.1 V

Discussion

8.	With a cell of emf 1.5 V, the balance point is obtained at a distance of 60 cm from one end of the potential wire. Calculate the potential difference between two ends of the potentiomter wire if its total length is 100 cm.
Answer» Correct Answer - 2.5 V

Discussion

9.	A galvanometer has a resistance of `15.0Omega` and the meter shows full scale deflection for a current of 2.0 mA. How will you convert this meter into (i) an ammeter of range 0-5.0A and (ii) a voltmeter of range 0 to 15.0V? Also determine the resistance of the meter in each case.
Answer» Correct Answer - (i). 0.006 `Omega` in parallel, `R_(A)=0.006Omega` (ii). `7485Omega` in series, `R_(V)=7500Omega`

Discussion

10.	A galvanometer has an internal resistance `1.0Omega`. It given maximum deflection for a current of 50 mA. Show how this instrument can be converted into (i) a voltmeter with a maximum reading of 2.5 V and (ii) an ammeter with a maximum reading of 2.5 A
Answer» Correct Answer - (i) `49Omega` in series (ii) `(1)/(49)Omega` in parallel

Discussion

11.	A galvanometer has a resistance of `49Omega`.If `2%` of the main current is to be passed through the meter, The value of the shunt will be
Answer» Correct Answer - `4Omega`

Discussion

12.	If a galvanometer is connected in series with a high resistance so that potential drop across the galvanometer is 1/n th of the total applied voltage, then show that the combined resistance of the galvanometer and the series resistor is n times the resistance of the galvanometer i.e.,
Answer» Correct Answer - `R_(V)=nR_(g)`.

Discussion

13.	AB is a potentiometer wire of length 100 cm. when a cell `epsi_(2)` is connected across AC, where AC=75cm, no current flows from `epsi_(2)`. Find (i) the potential gradient along AB and (ii) emf of the cell `epsi_(2)`. the internal resistance of the cell `epsi_(1)` is negligible.
Answer» Correct Answer - (i). 0.02 volt/cm, (ii). 1.5 V

Discussion

14.	In the circuit shown in figure. Find the currents `I,I_(1),I_(2) and I_(3)` given that emf of th battery=2V, internal resistance of the battery `=2Omega` and resistance of the galvanomter `=4Omega`.
Answer» Correct Answer - `I=(47)/(91)A,I_(1)=(17)/(91)A,I_(2)=(30)/(91)A,I_(3)=-(1)/(91)A`

Discussion

15.	The resistance of a potentiometer wire is `18Omega`. A high resistance box and a 2 V accumulator are connected in series with it. What should be the value of the resistance in the box, if it is desired to have a potential drop of `1muV//mm`?
Answer» Correct Answer - `1992Omega`

Discussion

16.	With a potentiometer, null points were obtained at 140 cm and 180 cm with cells of emf 1.1 volt and one of unknown value respectively. Calculate the unknown emf.
Answer» Correct Answer - 1.41V

Discussion

17.	A potentiometer wire of length 100 cm has a resistance of `10Omega`. It is connected in series with a resistance and an accumulator of emf 2V and negligible internal resistance. A source of emf 10 mV is balanced against a length of 40 cm of the potentiometer wire. what is the value of the external resistance?
Answer» Correct Answer - `790Omega`

Discussion

18.	A potentiometer having a wire 10 m long stretched on it, is connected to accumulator havig a steady voltage. A leclanche cell gives a null point at 750 cm. if the length of the potentiometer wire is increased by 100 cm, find the new position of the null point.
Answer» Correct Answer - 825 cm

Discussion

19.	Determine the current flowing through the galvanometer G of the Wheatstone bridge shown in figure. .
Answer» Correct Answer - 0.0454A

Discussion

20.	One ampere of current enters the junction A of a wheatstone bridge ABCD with `AB=2Omega,BC=2Omega,AC=4Omega,CD=2Omega and R_(g)=4Omega`. Find the current through the galvanometer.
Answer» Correct Answer - 0.25A

Discussion

21.	A current of 0.1 A enters a Wheatstone bridge consisting of three arms of `10Omega` each and one of `11Omega`. What is the current in galvanometer f its resistance is 100?
Answer» Correct Answer - `(1)/(4520)A`

Discussion

22.	Calculate the potential difference across the 2k `Omega` resistor in the circuit shown in figure. The internal resistance of the cells are negligible.
Answer» Correct Answer - 2V

Discussion

23.	calculate the current flowing in each of the resistances of the network shown in figure. The internal resistance of each cell is negligible.
Answer» Correct Answer - `-0.35A" along "DC,0.65"A alog BC",0.30"A along AC"`

Discussion

24.	A galvanometer has a sensitivity of 60 division/ampere. When a shunt is used its sentivity becomes 10 divisions/ampere. What is the value of shunt used if the resistance of the galvanometer is `20Omega`?
Answer» Correct Answer - `4Omega`

Discussion

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A galvanometer with a coil of resistance `10.0Omega` shows full scale deflection for a current of 50mA. How will you convert the galvanometer into (i). An ammeter of range 0 to 0.5 A and (ii). A voltmeter of range 0 to 5V?

A galvanometer of resistanece `40Omega` gives a deflection of 5 divisions per mA. There are 50 divisions on the scale. Calculate the maximum current that can pass through it when a shunt resistance of `2Omega` is connected.

A galvanometer has a resistance of `100Omega`. A difference of potential of 1.0 V between its terminals gives a full scale deflection. Calculate the shunt resistance which will enable the instrument to read upto 2A.

When a galvanometer having 20 divisions scale and `50Omega` resistance is connected in series to a cell of emf `1.5V` through a resistance of `100Omega`, its shows full scale deflection. Find the figure of merit of the galvanometer.

A certain length of a uniform wire of resistance `12Omega` is bent into a circle and two points, a quarter of circumference apart, are connected to a battery of emf 4 V and internal resistance `1Omega`. Find the current in the different parts of the circuit.

A potentiometer is being used to determine the internal resistance of a primary cell. The balance point for the cell in an open circuit is at 76.3 cm. when the cell sends a current in a resistor of `9.5Omega`, the balance point shifts to 64.8cm. Find the internal resistance of the cell.

With a certain cell, the balance point is obtained at 60 cm from the zero end of the potentiometer wire. With another cell whose emf differs from that of the first cell by 0.1 V, the balance point is obtained at 50 cm mark. Calculate the emf of the two cells.

With a cell of emf 1.5 V, the balance point is obtained at a distance of 60 cm from one end of the potential wire. Calculate the potential difference between two ends of the potentiomter wire if its total length is 100 cm.

A galvanometer has a resistance of `15.0Omega` and the meter shows full scale deflection for a current of 2.0 mA. How will you convert this meter into (i) an ammeter of range 0-5.0A and (ii) a voltmeter of range 0 to 15.0V? Also determine the resistance of the meter in each case.

A galvanometer has an internal resistance `1.0Omega`. It given maximum deflection for a current of 50 mA. Show how this instrument can be converted into (i) a voltmeter with a maximum reading of 2.5 V and (ii) an ammeter with a maximum reading of 2.5 A

A galvanometer has a resistance of `49Omega`.If `2%` of the main current is to be passed through the meter, The value of the shunt will be

If a galvanometer is connected in series with a high resistance so that potential drop across the galvanometer is 1/n th of the total applied voltage, then show that the combined resistance of the galvanometer and the series resistor is n times the resistance of the galvanometer i.e.,

AB is a potentiometer wire of length 100 cm. when a cell `epsi_(2)` is connected across AC, where AC=75cm, no current flows from `epsi_(2)`. Find (i) the potential gradient along AB and (ii) emf of the cell `epsi_(2)`. the internal resistance of the cell `epsi_(1)` is negligible.

In the circuit shown in figure. Find the currents `I,I_(1),I_(2) and I_(3)` given that emf of th battery=2V, internal resistance of the battery `=2Omega` and resistance of the galvanomter `=4Omega`.

The resistance of a potentiometer wire is `18Omega`. A high resistance box and a 2 V accumulator are connected in series with it. What should be the value of the resistance in the box, if it is desired to have a potential drop of `1muV//mm`?

With a potentiometer, null points were obtained at 140 cm and 180 cm with cells of emf 1.1 volt and one of unknown value respectively. Calculate the unknown emf.

A potentiometer having a wire 10 m long stretched on it, is connected to accumulator havig a steady voltage. A leclanche cell gives a null point at 750 cm. if the length of the potentiometer wire is increased by 100 cm, find the new position of the null point.

Determine the current flowing through the galvanometer G of the Wheatstone bridge shown in figure. .

One ampere of current enters the junction A of a wheatstone bridge ABCD with `AB=2Omega,BC=2Omega,AC=4Omega,CD=2Omega and R_(g)=4Omega`. Find the current through the galvanometer.

A current of 0.1 A enters a Wheatstone bridge consisting of three arms of `10Omega` each and one of `11Omega`. What is the current in galvanometer f its resistance is 100?

Calculate the potential difference across the 2k `Omega` resistor in the circuit shown in figure. The internal resistance of the cells are negligible.

calculate the current flowing in each of the resistances of the network shown in figure. The internal resistance of each cell is negligible.

A galvanometer has a sensitivity of 60 division/ampere. When a shunt is used its sentivity becomes 10 divisions/ampere. What is the value of shunt used if the resistance of the galvanometer is `20Omega`?