Ballistic galvanometer

Ballistic GalvanometerAnd experiment of finding the fixed capacity of condenser and also mutual inductance of

two coils.

Trisha Banerjee @ 2010

Ballistic Galvanometer


Phosphore bronze strip

mirror

copper coil

Soft iron core


Brief construction :-

The ballistic galvanometer is usually employed to measure the quantity of charge flowing in a given circuit due to transient current. it consists of a coil of copper wire wound on a non conducting frame which is suspended by a phosphor bronze strip between the poles of strong permanent magnet horse – shoe shape magnet . In order to increase the magnetic flux in the gap , the cylindrical soft iron – core is placed with in the coil. The pole pieces of the magnet are cylindrical concave in shape so that the magnetic field is radial in the narrow annular gap and is also perpendicular to the coil surface . The whole apparatus is covered in a shell to avoid disturbance from outside .Three leveling screws are provided below the base of the galvanometer . The deflection of the coil is measured by lamp and scale arrangement .

Note:- When large damping is present , the motion of the coil is non oscillatory and the moving coil galvanometer become dead beat . The construction and working of such a galvanometer is different from moving coil galvanometer.


Object :- to determine the absolute capacity of the condenser.

Apparatus':- Ballistics galvanometer with lamp and scale arrangement , two way morse key , a known high resistance , decade capacitor or condenser, and a Daniel cell with potential divider arrangement.


Trisha Banerjee@2010

Morse key

Reading the deflection from the scale.

Damping key

Morse key:-

It consists of a metal lever BCA and three terminals ABC fixed on a wooden base.A and B are connected to the metal studs just below the end a and B of the metal lever while C is connected to the metal support at the middle of the metal lever, connections between A and C is made on the releasing , the connections between A and C is made while A is cut off.


Fixed capacity condenser

Rheostat

Stop watch


Circuit diagram to finding the absolute capacity of a capacitor


Object to finding the mutual inductance of two coils.

Apparatus:- Ballistic galvanometer , Two coils , double tapping key, thick copper strip , small resistance , rheostat , Lechlanche cell , lamp and scale arrangement.

Circuit diagram for mutual inductance of two coils.


Scale

Ballistic

Lamp

Damping key

Double tapping key

Copper strip

Rheostat. ( small resistance)

coil


Double tapping Key:-


Double Tapping Key:-

The double tapping key has three strips XX’ , YY’ , ZZ’ mounted horizontally on ebonite rods . These rods are finally fitted on an ebonite base MN having a metal stud M. On depressing X, the contact is made between X and Y ( secondary SS) and between S and M ( primary PP). The strips Y and Z remains insulated by the ebonite strips in between them . When released the primary circuit is broken and then the secondary . When the current in primary is first cut off , current falls from maximum to zero , an instantaneous induced emf is developed in the secondary and a charge passes through the secondary and the galvanometer . Immediately the secondary circuit is broken , the suspended coil in the ballistic galvanometer deflects . The magnitude f the first throw depends on the quantity of charge that has passed through it.


Primary coil

Secondary coil


Technology

Ballistic galvanometer