It is the device which is used to measure the current with its direction.
Types of galvanometer-
- Moving Coil Galvanometer
- Moving Magnet Galvanometer.
Moving Coil Galvanometer are also of two types-
1. Suspended Coil Galvanometer –
Construction- It Consists of a rectangular coil of a large number of turns of thin insulated copper wire bound over a frame. This coil is suspended between the pole pieces of a horseshoes magnet.
This coil is suspended with the help of phosphor bronze wire. On this wire a small piece of plane mirror is also attached with the help of this mirror reflection of current is counted by lamp scale method.
2. Pivoted Coil Galvanometer –
The lower and portion of the coil is connected with spring and this is spring with is attached with da terminal on the other end and soft iron core is also Playster end the call to maximize the magnetic strength.
When a coil is placed between the new uniform magnetic field and some amount of current flows through the coils. There will be a torque acting on the coil which will tend to rotate the coil and magnet you torque is it directly proportional to the amount of current. Let in galvanometer a coil of area A, a number of turns N is placed in a uniform Magnetic field B and current I flow through the coil then the targeting on the coil will deflect the coil.
As due to the action of this torque coil rotate the bronze wire connected with the coil also get twisted then and there will be a restarting torque acting on the coil due to twist in wire and when a current is flowing through the coil of galvanometer due to torque acting on the coil. Coil on galvanometer rotate and the wire connected with the coil also gets a twist.
Let angle of twist is then the mirror connected on the wire will also show a deflection of angle in its orientation. Let the perpendicular distance of the mirror from the role is d while often the rotation deflected. Ray moves by d on the scale and we also know that if a mirror is rotated by an angle of the reflected ray will rotate by the angle the deflected can be connected.
Current Sensitivity Of Galvanometer –
If there is a variation in value of current then variation can be counted by galvanometer which is called its sensitivity. Deflection shown by galvanometer when a unit current flows through the circuit is called as current sensitivity and it is denoted by SI and its unit is per ampere.
Voltage sensitivity- Deflection per unit voltage is the difference is called voltage sensitivity of dielectric constant.
The Figure Of Merit – The figure of merit can be defined as the current required for unit deflection and galvanometer scale.
Conversion Of Galvanometer Into Ammeter or Voltmeter –
To convert a galvanometer into voltmeter and ammeter a small resistance wire is connected in the circuit parallel to the galvanometer. This small resistance is known as shunt wire and this also helps to avoid burning of galvanometer coil due to large amounts current.
Analysis of Shunt Wire –
Let a shunt wire of resistance x is connected in parallel to the galvanometer. Resistance of galvanometer is g. let current I flows through the circuit and ise is the current flowing through the galvanometer.
Conversion Of Galvanometer Into Ammeter –
To convert a galvanometer into ammeter we need to connect a shunt wire in parallel to the galvanometer. Let g is resistance of galvanometer. S is resistance of shunt wire and IG is current required for full deflection in galvanometer and I is the range of converted ammeter. Now this converted ammeter is connected in circuit. Ammeter is always connected in series combination and resistance of an ideal ammeter should be zero.
Conversion Of Galvanometer Into Voltmeter –
To convert galvanometer into voltmeter resistance of shunt wire is connected in series combination. Let resistance of the galvanometer is g and I g is the full deflection current and as is the resistance of the shunt wire. Let this converted voltmeter is connected in parallel combination across a resistance R and the potential difference is V.