Explain the difficulties occurred by using galvanometer directly as ammeter.

Explanation

1. To overcome these difficulties one attaches a small value resistance in parallel with galvanometer.

2. Shunt : A small value resistance connect parallel to galvanometer is known as shunt `(r_(s))`.
(i) As the value of shunt is very much smaller than galvanometer (G), most of the current passes through the shunt and galvanometer is protected against the damage.
(ii) Equivalent resistance of galvanometer and shunt is = `(R_(G)r_(s))/(R_(G)+r_(s))`
but `RGgtgtr_(s)` so we can neglect `r_(s)` at denominator,
= `(R_(G)r_(s))/R_(G)`
= `r_(s)`
`r_(s)` having very low value so original current does not changed.