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An ideal voltmeter and ideal ammeter should have

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Important Questions on Moving Charges and Magnetism

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

This question has

Statement I

and

Statement II

. Of the four choices given after the Statements, choose the one that best describes the two Statements.

Statement - I :

Higher the range, greater is the resistance of ammeter.

Statement - II :

To increase the range of ammeter, additional shunt needs to be used across it.

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

A galvanometer with its coil resistance

25 Ω

requires a current of

1 mA

for its full deflection. In order to construct an ammeter to read up to a current of

2 A

the approximate value of the shunt resistance should be:

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

A circuit contains an ammeter, a battery of 30 v and a resistance 40.8 ohm all connected in series. If the ammeter has coil of resistance 480 ohm and a shunt of 20 ohm, the reading in the ammeter will be:

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

A

B

and

C

are voltmeters of resistance

R

1 .5 R

and

3 R

respectively as shown in the figure. When some potential difference is applied between

X

and

Y

, the voltmeter readings are

V_{A}, V_{B}

and

V_{C}

respectively. Then:
Question Image

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

How is a galvanometer converted to an ammeter?

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

The reason a moving coil galvanometer cannot be used with an alternating current is that

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

A galvanometer, whose resistance is

50 ohm

, has

25

divisions in it. When a current of

4 \times 10^{- 4}

A passes through it, its needle (pointer) deflects by one division. To use this galvanometer as a voltmeter of range

2.5 V

it should be connected to a resistance of:

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

To know the resistance

G

of a galvanometer by half deflection method, a battery of emf

V_{E}

and resistance

R

is used to deflect the galvanometer by angle

θ

. If a shunt of resistance

S

is needed to get half deflection the

G

R

and

S

are related by the equation:

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

Derive the expression for the torque acting on the rectangular current carrying coil of a galvanometer. Why is the magnetic field made radial?

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

Define current sensitivity of a galvanometer. Write its expression.

HARD

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

In a circuit for finding the resistance of a galvanometer by half deflection method, a

6 V

battery and a high resistance of

11 kΩ

are used. The figure of merit of the galvanometer is

60 μA {division}^{- 1}

. In the absence of shunt resistance, the galvanometer produces a deflection of

θ = 9

divisions when current flows in the circuit. The value of the shunt resistance that can cause the deflection of

\frac{θ}{2}

, is closest to:

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

How do you convert a moving coil galvanometer into an ammeter?

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

Sensitivity of moving coil galvanometer is

s

. If a shunt of

{(\frac{1}{8})}^{t h}

of the resistance of galvanometer is connected to moving coil galvanometer, its sensitivity becomes

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

10 V

battery with internal resistance

1 Ω

and a

15 V

battery with internal resistance

0.6 Ω

are connected in parallel to a voltmeter (see figure). The reading in the voltmeter will be close to:

Question Image

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

A galvanometer having a coil resistance of

100 Ω

gives a full scale deflection, when a current of

1 mA

is passed through it. The value of the resistance, which can convert this galvanometer into ammeter giving a full scale deflection for a current of

10 A

, is:

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

50 Ω

resistance is connected to a battery of

5 V

. A galvanometer of resistance

100 Ω

is to be used as an ammeter to measure current through the resistance, for this a resistance

r_{S}

is connected to the galvanometer. Which of the following connections should be employed if the measured current is with in

1 %

of the current without the ammeter in the circuit?

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

A galvanometer has a 50 division scale. Battery has no internal resistance. It is found that there is deflection of 40 divisions when $R.B. = 2400 Ω .$ Deflection becomes 20 divisions when resistance taken from resistance box is 4900 Ω. Then we can conclude :

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Note: This question is awarded as the bonus. Now the question is corrected.

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

The galvanometer deflection, when key $K_{1}$ is closed but $K_{2}$ is open, equals $θ_{0}$ (see figure). On closing $K_{2}$ also and adjusting $R_{2}$ to $5 Ω,$ the deflection in galvanometer becomes $\frac{θ_{0}}{5} .$ The resistance of the galvanometer is, then, given by [Neglect the internal resistance of battery]:

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

Distinguish between ammeter and voltmeter.

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Physics>Electricity and Magnetism>Moving Charges and Magnetism>Electrical Instruments

When a current of

5 mA

is passed through a galvanometer having a coil of resistance

15 Ω

, it shows full-scale deflection. The value of the resistance to be put in series with the galvanometer to convert it into a voltmeter of range

0 - 10 V

is:

An ideal voltmeter and ideal ammeter should have

Important Questions on Moving Charges and Magnetism

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