Question 11:
moderateA milli voltmeter of $25 text{ milli volt}$ range is to be converted into an ammeter of $25 text{ ampere}$ range. The value (in ohm) of necessary shunt will be :
(2012 Pre)
The required shunt is $S = \frac{V_m}{I} = \frac{25 \times 10^{-3} \text{ V}}{25 \text{ A}} = 0.001 \Omega$.
Question 12:
moderateA galvanometer of resistance, $G$, is shunted by a resistance $S \text{ ohm}$. To keep the main current in the circuit unchanged, the resistance to be put in series with the galvanometer is :
(2011 Mains)
To keep the total resistance equal to $G$, the series resistance $R'$ must satisfy $R' + \frac{GS}{G+S} = G$, which simplifies to $R' = \frac{G^2}{S+G}$.
Question 13:
moderateA galvanometer has a coil of resistance $100 \Omega$ and gives a full scale deflection for $30 \text{ mA}$ current. If it is to work as a voltmeter of $30 \text{ V}$ volt range, the resistance required to be added will be :
(2010 Pre)
The required series resistance is $R = \frac{V}{I_g} - G = \frac{30}{30 \times 10^{-3}} - 100 = 1000 - 100 = 900 \Omega$.
Question 14:
moderateThe resistance of an ammeter is $13 \Omega$ and its scale is graduated for a current upto $100 \text{ amps}$. After an additional shunt has been connected to this ammeter, it becomes possible to measure currents upto $750 \text{ amperes}$ by this meter. The value of shunt resistance is :
(2007)
The shunt resistance is calculated as $S = \frac{I_g G}{I - I_g} = \frac{100 \times 13}{750 - 100} = \frac{1300}{650} = 2 \Omega$.
Question 15:
moderateA galvanometer acting as a voltmeter will have :
(2004)
A voltmeter is constructed by connecting a very high resistance in series with a galvanometer coil to measure potential difference safely.