Apparatus:
A low resistance galvanometer, a cell, two resistance box, two one way plug keys, connecting wires and sand paper.
Theory:
Set the circuit according to the figure. When only K, is closed the current. Through galvanometer is Set the circuit according to the figure. When only K, is closed the current. Through galvanometer is.
Where G resistance of galvanometer
E= e.m.f of cell
As current is proportional to the deflection in the galvanometer
When K2 also closed and adjusting S to get half deflection the current through galvanometer is
Procedure:
1. Draw a neat diagram of the circuit and make tight connection accordingly. The plugs to the key k1 and k2 must be taken out before making the connection.
2. Remove a plug of high resistance from the resistance box r and close the key k1 Adjust the resistance r to get a large deflection, within the scale the deflection must be in even number of divisions. Note the deflection and the value of the resistance r.
3. Now close the key K2 this reduced of the deflection zero. Adjust the shunt resistance make the deflection one half on its previous value note the value of the shunt resistance s for which the deflection in the galvanometer is
4. Repeat the experience by adjusting the deflection of the galvanometer for other even divisions. Take at lea st four readings.
Observation and calculations:
|
NO of obs |
Resistance R
|
Deflection Q Div. |
Shunt resistance S Ώ |
Half deflection div. |
G=
Ώ
|
|
1 2 3 4 |
|
28 16 14 22 |
|
|
|
Mean value of G ……..Ohms
Precautions:
- The connection will be tight and neat.
- A large resistance R should be introduced before closing the key k1
- The galvanometer reading should be taken in even divisions.
Viva voice:
Q.1: why galvanometer has resistance?
Ans: the resistance of galvanometer is due to the wire of its coil.
Q2: Why the deflection becomes half after closing the shunt key ?
Ans: Half of the current passes through the galvanometer and passes through the shunt deflection also become half.
Q3: what is mean by the Ig?
Ans: Ig is called current for full scale deflection i.e. the current which flows through the galvanometer that makes the deflection maximum within scale.
Q.1: why galvanometer has resistance?
Ans: the resistance of galvanometer is due to the wire of its coil.
Q2: Why the deflection becomes half after closing the shunt key ?
Ans: Half of the current passes through the galvanometer and passes through the shunt deflection also become half.
Q3: what is mean by the Ig?
Ans: Ig is called current for full scale deflection i.e. the current which flows through the galvanometer that makes the deflection maximum within scale.