Question

the resistance of a moving coil galvanometer is 195 ohm and its full scale deflection current is 100mA. the resistance required to be connected to convert it into ammeter of range of 4 A is​

Answer 1

Given :

Resistance of the galvanometer ($R_g$) = 195 ohm

Full scale  deflection current   = 100 mA

Range of ammeter = 4 A

To Find  :

The resistance of shunt (S) required = ?

Solution :

We know that for converting a galvanometer into an ammeter we need a shunt ( a very small resistance) in parallel with the galvanometer .

Now we will use the formula :

$i = i_g(\frac{R_g + S}{S})$

On putting the given values in this formula we get the value of S as :

$4 = 100 \times 10 ^{-3}\times (\frac{195 + S}{S})$

Or,$4 = \frac{1}{10}\times (\frac{195 + S}{S})$

Or, $40 S - S = 195$

Or ,$S =\frac{195}{39}$

Or, S = 5 ohm

So, the resistance of  shunt required is 5 ohm .