Content Strategy Manager
To convert given galvanometer into ammeter of desired range with verification, a low resistance in parallel is connected with galvanometer coil. A galvanometer can be converted into an ammeter. The parallel low resistance is also called as shunt. Galvanometer is used for detecting feeble electric currents in circuits. For this experiment a Weston Galvanometer with pivoted coil is used.
Also read: Difference Between Galvanometer and Ammeter
| Table of Content |
Key Terms: Galvanometer, Ammeter, Rheostat, Magnetic field, Low resistance, Pivoted coil, Electric current, Shunt, Concave pole, Circuit, Magnet
What is Galvanometer?
[Click Here for Sample Questions]
Galvanometer is an instrument that is specifically used for detecting and measuring weak electric currents in a circuit. Between the concave pole faces of a strong laminated horseshoe magnet, it has a suspended coil which is also described as a pivoted coil. This pivoted coil deflects when an electric current passes through it. The deflection is proportional to the electric current passing through the coil.
Working of Galvanometer
Deflection of the coil can be read with the help of a pointer attached to the galvanometer. The general resistance of a galvanometer coil is about 100 ohms and thus the galvanometer itself features a small current which features a capacity of 1 mA. Galvanometers were indeed the very first device to detect and measure the weak currents which are very small in amounts. A galvanometer can be used as an ammeter or voltmeter if suitable modifications are made.
Also Read:
What is Ammeter?
[Click Here for Previous Year Questions]
Ammeter is an instrument that is generally used for measuring electric current in the amperes. By using ammeters, a wide range of current values can be measured, because at high values only a small amount of the electric current is directed through the meter. In the ammeter, the shunt is parallel with the meter which carries the major portion of the current. There are digital ammeters that are nowadays used widely. Ammeters do vary in terms of their accuracies and operating principles.
There are different types of ammeters for example, - electrodynamic ammeter, D’Arsonval-movement ammeter, thermal ammeter, digital ammeter etc. The D’Arsonval-movement ammeters measures direct current with accuracies ranging from 0.1 to 2.0 percent, while electrodynamic ammeter measures direct as well as alternating current with accuracies from 0.1 to 0.25 percent. Thermal ammeter is used primarily to measure alternating current ranging from 0.5 to 3 percent, on the other hand, digital ammeters measures continuous current with accuracy up to 0.1 percent.
Uses of Shunt
[Click Here for Sample Questions]
An instrument that allows electric current to pass through another point in the circuit is called a Shunt. Shunt creates a low resistance path to smoothly pass the electric current to another point. A shunt which is also called an ammeter shunt is a highly accurate resistor that can be used to measure the electric current flowing through a circuit. The uses of a shunt are as follows:
- Diverting a large part of the total current by providing an alternate path. By doing this, the shunt protects the device from being damaged.
- The range of an ammeter can be increased by using a shunt.
- It decreases the resistance between the points of the circuit through which the shunt is connected.
Also Read:
Experiment Convert Given Galvanometer into Ammeter of Desired Range
[Click Here for Previous Year Questions]
Aim of Experiment
To convert the given Galvanometer of known resistance and figure of merit into an Ammeter of the specified range with verification of the same.
Apparatus
The following materials are required to perform the given experiment: -
- Weston galvanometer
- Ammeter with the range of 0-3 A
- The battery having two cells
- One-way keys – two
- Two resistance boxes of 10,000 Ω and 200 Ω
- Rheostat
- A piece of sandpaper
- Connecting wires
Theory of Experiment
For conversion of galvanometer into an ammeter the shunt resistance is required, the formula for the same is -
S = Ig – G/ I – Ig
I is the range of conversion.
Conversion of Galvanometer into Ammeter of Desired Range
Procedure of Experiment
- Firstly count the total amount of divisions on one of the sides of zero of the galvanometer scale. Let it be ‘n’.
- Now, calculate the current i.e., (Ig) for full-scale deflection which will be Ig = nk
- As mentioned above the shunt resistance value is calculated using S = Ig – G/ I – Ig
- The range will not be available in the resistance box because the shunt resistance has a small value. Wires of suitable length and diameter is used to get the value of small resistance.
- The wires can be copper, manganin, eureka, etc.
- Cut the wire more than 2cm from the obtained calculated value of I. Now, mark two points one cm away from each end of the wire. Considering that the marked points are just outside the terminal screws, connect the wire to both the terminals of the galvanometer.
- Make the electric connections just as same as in the diagram above.
- Insert the key and adjust the rheostat to observe and study the highest and the lowest deflection in the galvanometer.
- Note the reading on the galvanometer scale. Also, note the corresponding reading of the ammeter.
- Record your final observations.
Calculations
Resistance of galvanometer i.e., G = ___
Figure of merit, k = ___
Number of divisions in the galvanometer scale will be, n= ___
Full – scale deflection current can be obtained by this formula, Ig = nk
Range of conversion, I = ___
Therefore, Shunt resistance, S = Ig – G/ I – Ig = ___
Result and Precautionary Measurements
The difference between the actual and obtained value of currents is very small. Therefore, the conversion is perfect.
- The resistance should be calculated accurately.
- The length of the shunt wire should be long or small. It should be well measured and of perfect length.
- For the verification same range should be used for the conversion of ammeter.
Things to Remember
- Because the galvanometer can’t measure heavy currents, we have to use a shunt to convert the galvanometer into an ammeter.
- The device which measures the quantity of the current in the device is called an ammeter.
- A Weston type of galvanometer with a pivoted coil is used to perform the experiment.
- The shunt allows the current to pass through another point of the electric circuit.
- Ammeters are the most portable, widely used, and accurate device to measure the current in the circuit.
Also Read:
Sample Questions
Ques. A galvanometer has a resistance of 100 Ω and its full-scale deflection current is 100 μ A. To obtain the range of 0 to 10 mA in an ammeter what shunt resistance should be added? (3 Marks)
Ans. Given Ig= 100
μ A = 0.1 mA
I = 10 mA which is the upper limit that gives the maximum current if measured.
The galvanometer resistance is G= 100 Ω
Now, n = 10/ 0.1 = 100
Therefore, s = G / n-1 = 100/100-1 = 100/ 99 Ω
Ques. What do you mean by the figure of merit of the Galvanometer? (2 Marks)
Ans. In the galvanometer, to produce the deflection of one division the current is required. The quantity of that current is called the figure of merit of the galvanometer. The figure of merit is generally the numerical value that describes the efficiency of the device. The figure of merit is represented by the symbol k and the unit for the same is ampere per division.
Ques. Define shunt. What are the uses of shunt? (3 Marks)
Ans. An instrument that allows electric current to pass through another point in the circuit is called as a Shunt. It is also called an ammeter shunt. Shunt creates a low resistance path to smoothly pass the electric current to another point.
A shunt can be used in various ways. The uses of a shunt are as follows:
- Diverting a large part of the total current by providing an alternate path. By doing this, the shunt protects the device from being damaged.
- The range of an ammeter can be increased by using a shunt.
- It decreases the resistance between the points of the circuit through which the shunt is connected.
- Also used as diodes.
- Ammeter shunt is a highly accurate resistor which can be used to measure the electric current flowing through a circuit.
Ques. Write the definition of an ammeter and its uses. (3 Marks)
Ans. Ammeter is an instrument that measures the current in its unit i.e., amperes. It is like any other device which is used to measure the quantity. So, the ammeter measures the quantity of the current flowing through the device in the unit amperes.
Following are the uses of an ammeter:
- To check the temperature, it is used with a thermocouple.
- It is also used by electricians to check the faults in the circuits of electronic devices.
- It is used widely from school laboratories to industries.
- The first and foremost use of an ammeter is to measure the current in the circuit.
- As it is the most accurate device to measure the current, you can get accurate results while performing the experiment or checking faults in the electronic devices.
Ques. What are the merits and demerits of an ammeter? (3 Marks)
Ans. The merits of the ammeter are as follows:
- It is the most accurate device to measure the current.
- To measure the magnitude of current in an electric circuit, the ammeter is used.
- It can be used in both AC and DC measurements.
- Ammeter as compared to other devices is portable and strong.
The demerits of the ammeter are as follows:
- The data on the ammeter can’t be stored for future use.
- It gets heated while in use, which sometimes may affect the permanent magnet.
- Ammeter being a widely used device is far more expensive than the other measuring devices.
- Though it is portable, the ammeter is heavy in weight.
Ques. To convert a galvanometer into an ammeter, why do we use shunt? (2 Marks)
Ans. A galvanometer cannot measure the heavy currents. It can only measure currents that are weak. So, if we have to measure the high current, we first have to convert the galvanometer into an ammeter. To do that a shunt needs to connect parallel to the galvanometer so as to convert it into an ammeter because the shunt allows the electric current to pass around another point of the circuit.
Ques. What are the different types of galvanometers? (3 Marks)
Ans. A galvanometer is widely used in schools to industries. Here are some different types of galvanometers:
- Weston type, D’Arsonval, and moving coil are the most popular types of galvanometers.
- A ballistic galvanometer is used to detect and measure the charge.
- Periodic galvanometers are used to detect the potential difference and charge in the circuit.
- Based on construction, the moving coil and moving magnet galvanometers can be differentiated. In the moving coil, there are pivoted and suspended galvanometers.
- Universal tangent, kelvin astatic, pouillet tangent, and horizontal are some other types of galvanometers used.
Ques. Why is a moving coil galvanometer converted into a voltmeter? (3 Marks)
Ans. To measure the potential difference between two points of the electrical circuit, a voltmeter is used. The voltage drop is to be measured with the component which is connected parallelly. For this process, a moving coil galvanometer is used.
To convert the MCG (Moving coil galvanometer) into voltmeter certain modifications are required. Like, its effective resistance should be increased, and its voltage measuring capacity should be increased to the desired higher value. If these requirements are fulfilled, you can connect a resistance of suitable high value in the MCG and can convert it into a galvanometer.
Ques. What is a galvanometer? (1 Mark)
Ans. It is a device (instrument) used for detecting feeble electric currents in circuits.
Ques. Why the divisions of a galvanometer scale are equally spaced? (2 Marks)
Ans. Deflection in the pointer is proportional to the current passed. The number of divisions in deflection will be proportional to the current passed. I ∝= ∅.
Ques. How does the low resistance in parallel (shunt) give required properties to the galvanometer? (2 Marks)
Ans. The shunt reduces the overall resistance of the ammeter (converted galvanometer) and increases its current-carrying capacity.
Ques. How the high resistance in series gives required properties to the galvanometer? (2 Marks)
Ans. The series high resistance increases the overall resistance of the voltmeter (converted galvanometer) and decreases its current-carrying capacity.
Previous Year Questions
- A junction diode has a resistance of 25 O when forward biased… [WBJEE 2009]
- Pure Si at 500K has equal number of electron… [NEET 2011]
- The barrier potential of a p−n junction depends on (1) type of semiconductor… [NEET 2014]
- The depletion layer in the p-n junction region is caused by… [NEET 1991]
- A galvanometer acting as a voltmeter should have…?
- A galvanometer having a coil resistance of 60 ohms shows full scale deflection when a current of…?
- A galvanometer having a resistance 12Ω gives a full scale deflection for a current of…?
- A galvanometer having a resistance of 8 Ω is shunted by a wire of resistance 2 Ω. If the total…?
- A moving coil galvanometer of resistance 100 Ω is used as an ammeter using a resistance…?
- A galvanometer having a coil resistance of 100Ω gives a full scale deflection, when a current…? [JEE 2016]
- A galvanometer of resistance G is converted into a voltmeter of range 0−1V by connecting a resistance…? [JEE 2020]
- A galvanometer, whose resistance is 50ohm, has 25 divisions in it. When a current…? [JEE 2019]
- When a current of 5mA is passed through a galvanometer having a coil of resistance…? [JEE 2017]
- The current sensitivity of a moving coil galvanometer depends on…? [VITEEE 2018]
- A galvanometer has a resistance G and a current flowing in it produces full scale deflection…? [KCET 2019]
- A galvanometer can be converted into a voltmeter by connecting…? [NEET 2012]
- A galvanometer acting as a voltmeter will have…? [VITEEE 2017]
- A galvanometer with a scale divided into 100 equal divisions has a current sensitivity…? [VITEEE 2015]
- A galvanometer has a resistance of 50Ω. If a resistance of 1Ω is connected across its terminals…? [DUET 2006]
- In a tangent galvanometer, a current of 1A produces a deflection of…? [VITEEE 2006]
For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates
Check-Out:
Comments