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Ammeter and Galvanometer are used to measure current in an electric circuit. Besides this, both of them have many differences as well. The main difference is that a galvanometer shows the direction, as well as the magnitude of the electric current and an Ammeter, shows the magnitude of the electric current. In this article, you will learn about both of these instruments and their differences.
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Keyterms: Ammeter, Galvanometer, current, electric circuit, electric current, Amperes, microampere, milliampere
Ammeter
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An ammeter is an instrument that is used to measure the current in a circuit. The measurement of an electrical current is named after the renowned scientist known as Sir Ampere and is measured in Amperes. The currents that are smaller in the range such as microampere or milliampere are calculated by this instrument.
Ammeter
In 1820, Hans Christian Orsted became the first person to find the relation between forces of electric current and magnetic fields. He observed that when the flowing current in the wire was adjacent, the needle of the compass got deflected towards the north direction. The galvanometer was used to measure the same currents with this effect. It can be said that the earth's magnetic forces caused the restoration of the pointer to zero position. So, these instruments were only usable when they were aligned with the earth's field.
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Galvanometer
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An electromechanical instrument used for detecting and indicating an electrical current is known as a Galvanometer. A galvanometer works as an actuator which works by producing a rotary deflection of a pointer. In response, the electric current flows through a coil in a constant magnetic field. These measure the current which flows through an electric circuit.
Galvanometer
The Galvanometers work by deflecting the needle of the magnetic compass near a wire that has an electric current flowing through it. This was first discovered in the year 1820 by Hans Christian Ørsted.
The galvanometer has been constantly important for the development of technology and science in various fields. For example, they enabled long-range communication used through submarines and for cables as early as the transatlantic telegraph cable.
All these discoveries were essential for the further discoveries of various different advanced technologies in medical science as well, such as the measurement of electrical activity inside the heart and brain, which was only detectable through fine measurement-making devices.
Galvanometer
Difference between Ammeter and Galvanometer
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There are many differences between an Ammeter and a Galvanometer, for example:
- A galvanometer uses a moving coil that is free to rotate between the permanent magnets. When the current starts flowing through the coil, the needle inside it gets deflected. The deflection of the needle in the coil is directly proportional to the current flowing through it. A galvanometer can be converted into an Ammeter by connecting the resistance parallel with the circuit, however, if the resistance in it is connected in series with the galvanometer, then it becomes a voltmeter.
- The ammeter is also known as the ampere meter, as the unit of electric current is ampere. Ammeter is the type of meter which measures the magnitude of current passing through the wire. It is connected in series with the circuit for determining the exact value of an electric current.
There are various other differences between an Ammeter and a Galvanometer. Some of the key differences are tabulated below:
| Ammeter | Galvanometer |
|---|---|
| It is used to determine the magnitude of an electric current flowing in a circuit. | It is used to detect the direction and strength of a small current running through a circuit. |
| It can work regardless of the presence of a magnetic field. | It works because of the presence of the magnetic field. |
| It measures both the Direct current and Alternate current. | It only measures the direct current. |
| It is less sensitive as compared to others. | It is more sensitive when compared to others. |
| It has higher accuracy. | It has lower accuracy. |
| It can be either electronic or mechanical. | It can only be electromechanical. |
| It is used to detect current in electric circuits. | It is used to detect current in bridges and potentiometers. |
Things to Remember
- The galvanometer shows the direction of flow of current in the circuit whereas an Ammeter measures the magnitude of the ammeter of current flowing in a circuit.
- A magnetic field is required for the function of the Galvanometer, however, it is not required for the function of the Ammeter.
- The Ammeter has more accuracy than the Galvanometer.
- A galvanometer can only be used for measuring DC however An Ammeter can be used to measure both AC and DC.
- A Galvanometeris more sensitive as compared to an Ammeter.
- A Galvanometer is used mostly in bridges and potentiometers for measuring the current that is zero, however, an Ammeter is direct to the Circuit in series, whose magnitude should be mentioned.
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Important Questions
Ques: Why is the resistance of an ammeter kept low? (1 Mark)
Ans: The resistance of an ammeter is kept low because if the resistance is kept high then the current passing through the circuit will decrease.
Ques: Why is an ammeter always connected in series? (1 Mark)
Ans: An ammeter is always connected in series because the internal resistance of an ammeter should be kept low. If the ammeter will be connected in parallel, it will do a short circuit.
Ques: What does a Galvanometer Measure? (1 Mark)
Ans: A galvanometer is an instrument that can detect and measure small amounts of current in an electric circuit.
Ques: What is the resistance of an ammeter? (1 Mark)
Ans: The resistance of an ammeter is very small and for an ideal ammeter, its value is zero.
Ques: How can a galvanometer be used as an ammeter? (2 Marks)
Ans: Large currents can be detected by converting a Galvanometer into an Ammeter. To convert a galvanometer into an ammeter, connect a low resistance known as shunt resistance parallel to the galvanometer.
Ques: What is shunt resistance? (2 Marks)
Ans: Shunt resistance is a resistor with a low value of resistance. A low-temperature coefficient resistance is a material used inside a shunt Resistance. When it is connected in parallel with an ammeter, it can be used for measuring the extended range when it is connected in parallel with an Ammeter. The current through the load can be determined if the resistance is connected to the load in series. A Galvanometer can be converted into an Ammeter by using a Shunt Resistance.
Ques: A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet with its north pole towards one face of the coil is
(i) moved quickly towards it,
(ii) moved quickly away from the coil and
(iii) placed near its one face?
Name the phenomenon involved. (3 Marks)
Ans: (i) If the bar magnet is moved quickly towards the coil, the deflection in the galvanometer needle will be more on the right-side.
(ii) If the bar magnet is moved away from the coil then the larger deflection in the opposite direction will be seen.
(iii) If the bar magnet is placed near the coil then no deflection will be observed.
The phenomenon involved in this is electromagnetic induction.
Ques: Two coils A and B of insulated wires are kept close to each other. Coil A is connected to a galvanometer while coil B is connected to a battery through a key. What would happen if
(i) a current is passed through coil B by plugging the key, and (ii) the current is stopped by removing the plug from the key?
Explain your answer mentioning the name of the phenomenon involved. (3 Marks)
Ans: In both the given cases, the galvanometer shows momentary deflection but in opposite direction. In coil A, magnetic field lines induce a potential difference across coil A due to which induced electric current in coil A will set up. It is shown by the deflection in the galvanometer. This is known as electromagnetic induction.
(i) If the current is passed through coil B by plugging the key, the magnetic field lines will increase.
(ii) If the current is stopped by removing the plug from the key then the magnetic field lines will decrease.
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