Magnetic effects of current-III : Magnetic effects of current-III By R.Buvana
Current sensitivity : Current sensitivity Current sensitivity of a galvanometer is defined as the deflection produced in the galvanometer when a unit current flows through it.
Current sensitivity=?/I=nBA/k
The unit of current sensitivity is rad per A or div.per A
Voltage sensitivity : Voltage sensitivity Voltage sensitivity of a galvanometer is defined as the deflection produced in the galvanometer when a unit voltage is applied across the two terminals of the galvanometer.
Voltage sensitivity=?/V= ?/IR=nBA/kR
Conditions for a sensitive galvanometer : Conditions for a sensitive galvanometer A galvanometer is said to be very sensitive if it shows large deflection even when a small current is passed through it.
?=nBA/k I
For a given value of I,? will be large if nBA/k is large. It is so if
(a) n is large (c) A is large
(b) B is large (d) k is small
Ammeter : Ammeter An ammeter is a low resistance galvanometer . It is used to measure the current in a circuit in amperes. A galvanometer can be converted into an ammeter by using a low resistance wire in parallel with the galvanometer.
Ig G=(I-Ig)S Ig=nK
S=(Ig/I-Ig)G Where K is figure of merit or current for one scale deflection in the galvanometer.
Conti… : Conti… 1/Rp= 1/G+1/S
Rp=GS/G+S
As the shunt resistance is low, the combined resistance of the galvanometer and the shunt is very low and hence ammeter has a much lower resistance than galvanometer. An ideal ammeter has zero resistance.
Voltmeter : Voltmeter A voltmeter is a high resistance galvanometer. It is used to measure the potential difference between two points of a circuit in volt.
Ig=V/G+R
R=V/Ig -G
Rv=G+R.
For voltmeter, a high resistance R is connected in series with the galvanometer , therefore the resistance of voltmeter is very large as compared to that of galvanometer .The resistance of an ideal voltmeter is infinity.
Homework questions : Homework questions