electrical devices

 Some electrical devices

⦁    Rheostat: rheostat is a device by which current in an electric circuit is controlled. It is used as a potential divider and as a variable resistance.
To use it as a potential divider connection is made as: two end terminals are connect to a cell through a than the emf of the cell will be divided on the wire when the key is closed. Now, connect a circuit to which a variable potential difference is to be applied in between the top terminals T3 and any one of the end terminals of the wire.
To use it as a variable resistance: one connection is to made essentially at the top rod and the other connection is at any one of the ends of the wire.

⦁    galvanometer: a sensative current detecting device in an electric circuit is called galvanometer. it can measure very small amount of current in a circuit. so, it is also called as milli ammeter.
I.      moving magnet galvanometer:
II.    moving coil galvanometer:
    when current is passed through the coil it experiences a torque and     deflects. the deflection of a coil is directly proportional to current. it     is used as a main component in the construction of ammeter and     voltmeter.
⦁    Ammeter: a current measuring device in an electronic circuit is called an ammeter. To measure current, an ammeter is connected in series in a circuit. ammeter is also called a shunted galvanometer.ammeter cant have 0 resistance.
⦁    voltmeter: a voltage measuring device in an electric circuit is called a voltmeter. it is always connected in parallel across the points in the electric circuit. the voltmeter will draw the negligible current and which is possible in series with galvanometer only if resistance is very high. a voltmeter is a high resistance galvanometer. the higher the range of galvanometer, the higher resistance is usd. the ideal voltmeter has infinite resistance. it is not possible but only a supposition.
⦁    shunt: A low resistance connected in parallel  to the galvanometer to reduce its resistance is called shunt.
    uses:
i.    for converting galvanometer into ammeter.
ii.    reduce total resistance of ammeter.
iii.    prevent from the damage of galvanometer.
iv.    increases the range of ammeters.  

• Ohmmeter: A ohmmeter is a device to measure the resistance of a conductor. it is not a precision instruction. it is connected across the two terminals removing short circuit. the pointer directly indicates the value of R in the scale.