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To Convert Given Galvanometer into Ammeter of Desired Range with Verification

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To convert the given galvanometer into an ammeter of desired range and to verify the same we need to see the article in depth.

A Weston type galvanometer that is said to be an ammeter of 0-3 A. range and a battery which is of two cells or battery eliminator that is of two which is 10,000 Ω and 200 Ω resistance boxes there are two one way keys and a rheostat then the connecting wires and a piece of sandpaper.

The materials required

  • A galvanometer of Weston type

  • an Ammeter of the range 0-3 A

  • A Battery with two cells

  • And two resistance boxes that are of 10,000Ω and 200Ω respectively

  • Then Two one way keys

  •  Rheostat

  • Then the connecting wires

  • The piece of sandpaper

What is a Galvanometer 

We can also say that a galvanometer works as an actuator by producing a rotary deflection of a pointer that is in response to electric current which is flowing through a coil in a constant magnetic field. We can say that early galvanometers were not calibrated but now as we can see that the improved devices were used as measuring instruments known as the ammeters which in this article we will learn to measure the current flowing through an electric circuit.


The term that is galvanometers is developed from the observation that the needle of a magnetic compass which is said to be deflected near a wire that has electric current flowing through it was first described by Sir Hans Christian Ørsted in 1820. They were the first instruments that were used to detect and measure the very small amounts of electric currents. Sir André-Marie Ampère who gave mathematical expression to Ørsted's discovery and named the instrument after the Italian researcher who was Luigi Galvani who discovered the principle of the frog galvanoscope in 1719 – that electric current would make the legs of a dead frog jerk at that time.


What is an Ammeter 

An ammeter that is from an ampere meter is said to be a measuring instrument used to measure the current in a circuit. Electric currents which are generally measured in amperes that are denoted as A hence the name is an ammeter. The ammeter is usually said to be connected in series with the circuit in which the current is to be measured. An ammeter usually has a resistance which is low resistance so that it does not cause a significant drop of the voltage in the circuit being measured.


We can say that early meters were laboratory instruments that relied on the magnetic field of Earth's field for operation. By the late 19th century there were improved instruments which were designed which could be mounted in any position and allowed accurate measurements in the electric system of power. It is said to be generally represented by the letter denoted by  'A' in a circuit.


The majority of ammeters that are said to be either connected in series or with the circuit which is carrying the current to be measured that is for small fractional amperes or have their shunt resistors that are connected similarly in series. In either case, we can say that the current generally passes through the meter or we can say mostly through its shunt. Here we will say that the ordinary Weston-type meter movements can measure only milliamperes at most because the springs and practical coils can carry only limited currents. To measure the current which is larger a resistor known as a shunt is placed in parallel with the meter. 


Conversion of Galvanometer into Ammeter

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The Procedure 

  1. The count of the total number which is of divisions on either side of zero of the galvanometer scale. Let it be denoted by letter that is n.

  2. Then we need to calculate the current that is Ig for full-scale deflection that is  Ig = nk.

  3. Now we will calculate the value that is of resistance of shunt for conversion into ammeter that is said to be  using the formula:

S = \[\frac{I_{g}.G}{I-I_{g}}\]

Where letter that is I is the range of conversion.

The value which is of shunt resistance that is said to be denoted by letter S is usually very small and a resistance box of that range is not available. Such small resistances which are obtained by taking wires that are made of copper and constantan, manganin, eureka, etc., of a suitable diameter and length.

  1. Then we need to cut a length of the wire that is 2 cm more than the calculated value of the l.  We then need to mark two points on the wire that is one cm away from each end. Then we will connect this wire to the two terminals of the galvanometer such that the points which are marked are just outside the terminal screws. Then make the electric connections that are as shown in the circuit diagram.

  2. Then we need to insert the key and adjust the rheostat that is so that the galvanometer shows nearly maximum deflection.

  3. We need to note the reading which is on the galvanometer scale and also corresponding reading on the ammeter.

  4. Then we need to record our observations.


Result of the Experiment 

As the difference in the measured and actual value of currents that are as recorded in observation is very small that is the conversion is perfect.

FAQ (Frequently Asked Questions)

Q1. Explain How We Can Convert a Galvanometer into an Ammeter of Given Range?

Ans: generally we can say that it can be converted into an ammeter by connecting a resistance which is low resistance known as shunt resistance in parallel to the galvanometer. Ig is generally calculated using the equation that is written as Ig = nk where the term that is denoted by n is the number of divisions on the galvanometer and k is the figure of merit of the galvanometer.

Q2. Explain Why we Use a Shunt to Convert a Galvanometer into an Ammeter?

Ans: we can say that since a galvanometer is a very sensitive instrument that it can not measure the heavy currents. To do so that is A shunt is connected in parallel with a galvanometer to convert it into ammeter. so after doing that it can measure in the heavy currents in the circuit.

Q3. Explain How a Galvanometer Can be Converted into a Voltmeter?

Ans: A galvanometer can be converted into a voltmeter by connecting a large resistance that is in series to the galvanometer which is shown in the diagram in the article. This is said to be the required value of resistance which must be connected in series and that is to the galvanometer into a voltmeter of range 0-V volt.

Q4. Explain What the Half Deflection Method is?

Ans: A method that is of finding the internal resistance of a cell when the value is called to be high. We can say that the deflection of half the value which is obtained with the cell alone is found.