Topics Covered :
- What is Galvanometer ? & it’s Types
- Conversion to Ammeter
- Conversion to Voltmeter
- Some Examples
1. What is Galvanometer ?
Galvanometer is a deflection type meter which is used to measure the current value. The needle present in the Galvanometer gets deflected when a current passes through it and the amount of deflection produced is proportional to the current passing through the device.
There are two types of Galvanometers :
- Uni-Directional
- Bi-Directional
- Uni-Directional : In this case, the markings on the dial start from 0 till the maximum range. It has a red terminal which indicates that it has to be given high potential connection and the other one is black terminal for lower potential connection.
- Bi-Directional : The zero of the dial is in the center and we have the maximum on either side. So, from the direction of deflection, we get to know the direction of current in the conductor and the amount of deflection gives us the magnitude.
So, the basic difference between the two is that, Unidirectional can give information only about magnitude while Bi-directional can tell direction as well as magnitude.
The inner setup of Galvanometer has something known as Coil Resistance ‘G‘ and at maximum deflection, the safe current which flows through the galvanometer is ‘ig‘ . The symbol for Galvanometer is :
2. Conversion to Ammeter
The purpose of an Ammeter is also to measure current but the range for current measurement is much higher.
- How to Convert ? – Just add a resistor with very small resistance (Shunt ‘S’) in parallel to Galvanometer
What happens because of this ?
- Now suppose, ‘I‘ (I > ig) is the current flowing in conductor. Since S and G are connected in parallel, ‘I‘ will be divided in ‘ig‘ and ‘I-ig‘.
- The shunt resistance S, being very small in magnitude will attract a lot of current (since current always prefers least resistance path). The shunt resistance S, is the reason why we are able to supply a larger current than ig.
- This helps us to measure a larger current, resulting in increase in the range of the galvanometer
How to calculate this ‘I‘ ?
3. Conversion to Voltmeter
The Voltmeter is used specifically to measure the potential difference across the given terminals.
- How to Convert ? – Add a very high ‘Load’ resistance R in series to Galvanometer
What happens because of this ?
4. Examples
(Question from Arihant – Electricity and Magnetism)
Solution :
(Question from Arihant – Electricity and Magnetism)
Solution :
Conclusion :
So, we have learnt about the Galvanometer and how can we use it as an Ammeter and a Voltmeter.
- This topic is important from not only practical point of view but also theory exam point of view
- And other than marks, it’s always good to know about our electrical instruments !
All the Best !
