Converting a Galvanometer Into a Voltmeter of Desired Ranged

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Galvanometer is a device used to detect very low currents. The working of a galvanometer is based on the principle that a coil placed in a uniform magnetic field experiences a torque when an electric current is set up in it. On the other hand, Voltmeter is a high resistance device. The resistance of an ideal voltmeter is infinite. By connecting a high resistance of suitable value in series with the galvanometer, it is converted into a voltmeter. The voltmeter is connected parallelly with an electrical component across which potential difference is to be measured.

Read Also: Relation Between Gauss and Tesla

Table of Content

Aim
Apparatus
Theory
Diagram
Procedure
Observations
Precautions
Sources Of Error
Things To Remember
Sample Questions

Key Terms: Galvanometer, Voltmeter, Resistance, Torque, Rheostat, Torque, Electric current, Magnetic field, Coil

Aim

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To convert the given galvanometer of known resistance and figure of merit into a voltmeter of desired range and to verify it with an experiment.

Apparatus

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A galvanometer of known resistance with a figure of merit
A constant or manganin wire of 26 or 30 SWG
A battery or any battery eliminator
One way key
Rheostat of range 200 ohms
An emitter of 0-30 ml range
A voltmeter of three we range
Connecting wires and sandpaper

Theory

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By connecting a high resistance of suitable value in series with the galvanometer it is converted into a voltmeter. Voltmeter is always connected parallelly with the electrical component across which potential difference is to be measured.

If a galvanometer having resistance G, shows a full-scale deflection of a maximum current Ig and the potential difference from across the galvanometer is IgG. If the converted galvanometer is desired to have a range of Vo Volt, then the resistance to be joined in series with galvanometer, is given by the formula R = VoIg – G.

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Diagram

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Check Important Notes for Circuit Diagram

Procedure

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Calculate all the values of the series resistance R for given values of VO, Ig and of G.
Make the connection exactly as shown in the figure by connecting a cell and converted galvanometer and the voltmeter having nearly the same range in parallel with a high resistance rheostat Rh.
Close the key K and carefully adjust the rheostat so that the voltage shown in the voltmeter is equal to the desired range (say 3V).
Simultaneously adjust the position of the slider of the rheostat as well.
Adjust the resistance from the resistance box to make sure that when full scale deflection is observed on the galvanometer the voltmeter shows the exact value of the desired range (3V).
Keep a note of the total resistance from the resistance box.

Observations

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The given figure of merit of the galvanometer, k = ... ampere/division
Number of divisions on each side of zero of the galvanometer scale, N = ... division
Current required to produce full scale deflection of N divisions, Ig = k N = ... ampere

Precautions

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Do not use resistance box of low resistance.
The rheostat should only be used as the potential divider.
Using the exact same range conversion voltmeter for verification.
To avoid any damage to the galvanometer, the battery key should be closed.

Check Also: Ampere’s Circuital Law

Sources Of Error

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The wire might be of non-uniform area in cross section.
The resistance of the coils in the resistance box used may differ from the ones marked.
Loose plugs in the resistance box.

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Current Electricity: Important Questions and MCQs
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Things To Remember

If we connect a galvanometer in parallel to the circuit, it will draw some current and hence the potential difference of the circuit will be changed completely and also the measurement will not be accurate.
A voltmeter is always connected parallelly to the circuit component across which the voltage is to be measured.
Always use a rheostat as a current divider and a potential divider.
Measure θ in the same way 5 to 10 times to check if the friction in your instrument is small enough.

Also Read:

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Sample Questions

Ques: On what principle does galvanometer works? (2 marks)

Ans: A galvanometer works on the principle of torque acting on a coil that is carrying current, inside a magnetic field. The torque acting on the coil is directly proportional to the magnitude of an electric current flowing through it. Also, the coil is connected to a pointer that makes the pointer of the galvanometer calibrated so that it shows correct deflection on a scale.

Ques: What is a Voltmeter? (2 marks)

Ans: A voltmeter is an electric instrument used to measure electric potential difference between two points in a circuit. It usually has high resistance and are connected parallelly to the circuit. Voltmeters are made of different styles, some separately powered like batteries, and some powered by the measured voltage source itself.

Ques. How is galvanometer converted into a voltmeter? (2 marks)

Ans: A galvanometer can be converted into a voltmeter by simply connected a high resistance in series of the galvanometer because a galvanometer has resistance of order 60 or 70 ohm while voltmeter has very high resistance.

Ques: What are the types of a galvanometer? (2 marks)

Ans: Some galvanometers use a solid pointer on a scale to show the measurements whereas other sensitive types use a miniature mirror and beam of light to provide mechanical amplification of the low-level signals. Based on the construction of galvanometer they are classified into two types moving coil and moving magnet. It may be of two types pivoted and suspended. Here the types of galvanometers based on their uses like ballistic and dead beat.

Ques: Define resistance of an ideal voltmeter. (2 marks)

Ans: The resistance of an ideal voltmeter should be Infinity because no current flows from it and the resistance of an ideal ammeter is zero. Ammeter is connected in series and voltmeter is connected parallelly with the electric appliance.

Ques: Difference between voltmeter and voltameter. (2 marks)

Ans: Voltammeter is and electrolytic cell that is used to carry out the process of electrolysis whereas voltmeter is an instrument used for measuring the potential difference of two points in a particular circuit. The voltameter should not be confused with a voltmeter, which measures electric potential, the SI unit for electric potential is the volt.

Ques: How does a galvanometer work? (2 marks)

Ans: A galvanometer is a sensitive device that detects the small current. It can be easily converted into an emitter and a voltmeter. If we connect a galvanometer in Wheatstone’s bridge circuit the pointer in the galvanometer shows null deflection meaning that no current flows through the device, however if the pointer reflects towards the left or the right that means the current starts flowing through the direction of deflection depending on the direction of the current. Although, the conversion of galvanometer into an ammeter or voltmeter requires a good understanding of interconnection as galvanometers are very sensitive for detecting the current.

Ques: What is a rheostat? (2 marks)

Ans: Rheostat is an electrical device that is used in many applications that requires the adjustment of current or the wiring resistance in an electric circuit. This device was named Rheostat after two Greek words “rheos” and “status” meaning a current controlling device. Rheostats are two-terminal devices, one connected to the wiper and another one connected to an end of the resistance track.

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Converting a Galvanometer Into a Voltmeter of Desired Ranged

Aim

Apparatus

Theory

Diagram

Procedure

Observations

Precautions

Sources Of Error

Things To Remember

Sample Questions

CBSE CLASS XII Related Questions

1.
What is displacement current (\( i_d \))? Considering the case of charging of a capacitor, show that \( i_d = \varepsilon_0 \frac{d\Phi_E}{dt} \). What is the value of \( i_d \) for a conductor across which a constant voltage is applied?

2.
Four independent waves are expressed as \[ (i)\; y_1=A_1\sin\omega t, \] \[ (ii)\; y_2=A_2\sin 2\omega t, \] \[ (iii)\; y_3=A_3\cos\omega t, \] \[ (iv)\; y_4=A_4\sin\left(\omega t+\frac{\pi}{3}\right) \] The interference between two of these waves is possible in

3.
Draw the number of scattered particles versus the scattering angle graph for scattering of alpha particles by a thin foil. Write two important conclusions that can be drawn from this plot.

4.
If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.

5.
Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field \( \mathbf{B} \) at a point \( (1 \, \text{m}, 1 \, \text{m}, 0) \).

6.
Write any two features of nuclear forces.

Comments

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Converting a Galvanometer Into a Voltmeter of Desired Ranged

Aim

Apparatus

Theory

Diagram

Procedure

Observations

Precautions

Sources Of Error

Things To Remember

Sample Questions

CBSE CLASS XII Related Questions

1.What is displacement current (\( i_d \))? Considering the case of charging of a capacitor, show that \( i_d = \varepsilon_0 \frac{d\Phi_E}{dt} \). What is the value of \( i_d \) for a conductor across which a constant voltage is applied?

2.Four independent waves are expressed as \[ (i)\; y_1=A_1\sin\omega t, \] \[ (ii)\; y_2=A_2\sin 2\omega t, \] \[ (iii)\; y_3=A_3\cos\omega t, \] \[ (iv)\; y_4=A_4\sin\left(\omega t+\frac{\pi}{3}\right) \] The interference between two of these waves is possible in

3. Draw the number of scattered particles versus the scattering angle graph for scattering of alpha particles by a thin foil. Write two important conclusions that can be drawn from this plot.

4. If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.

5.Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field \( \mathbf{B} \) at a point \( (1 \, \text{m}, 1 \, \text{m}, 0) \).

6. Write any two features of nuclear forces.

Comments

SUBSCRIBE TO OUR NEWS LETTER

1.
What is displacement current (\( i_d \))? Considering the case of charging of a capacitor, show that \( i_d = \varepsilon_0 \frac{d\Phi_E}{dt} \). What is the value of \( i_d \) for a conductor across which a constant voltage is applied?

2.
Four independent waves are expressed as \[ (i)\; y_1=A_1\sin\omega t, \] \[ (ii)\; y_2=A_2\sin 2\omega t, \] \[ (iii)\; y_3=A_3\cos\omega t, \] \[ (iv)\; y_4=A_4\sin\left(\omega t+\frac{\pi}{3}\right) \] The interference between two of these waves is possible in

3.
Draw the number of scattered particles versus the scattering angle graph for scattering of alpha particles by a thin foil. Write two important conclusions that can be drawn from this plot.

4.
If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.

5.
Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field \( \mathbf{B} \) at a point \( (1 \, \text{m}, 1 \, \text{m}, 0) \).

6.
Write any two features of nuclear forces.