Question

This question has Statement I and Statement II. Of the four choices given after the statements, choose the one that best describes into two Statements.
Statement-I : Higher the range, greater is the resistance of ammeter.
Statement- II : To increase the range of ammeter, additional shunt needs to be used across it.
A. Statement-1 is true, Statement-2 is true, Statement-2 is a correct explanation of Statement-1.
B. Statement-1 is true, Statement-2 is true, Statement-2 is not a correct explanation of Statement-1.
C. Statement-1 is true, Statement-2 is false.
D. Statement-1 is false, Statement-2 is true.

Answer 1

Hint: Galvanometer is an electronic device which can be converted into ammeter or voltmeter. It depends on the type of connection we give to external resistance. If we connect small resistance in parallel to the galvanometer then it would become an ammeter and if we connect big external resistance to the galvanometer in series then it would become voltmeter.
Formula used:
$S = \dfrac{{{i_G}G}}{{i - {i_G}}}$
$V = IR$

Complete answer:
In case of parallel connection of resistors which means that the voltage across the two resistors will be same and current passing through the resistors vary.
We have
$V = IR$
Where V is the voltage and I is the current and R is the resistor.
If it is in a parallel connection then voltage will be the same and current is inversely proportional to voltage.
In case of ammeter shunt resistance (S) will be connected in parallel to galvanometer resistance (G). current passing through total ammeter is $'i'$ and the current passing through galvanometer resistance is ${i_G}$ so the current passing through shunt resistor is $i - {i_G}$
Voltage across galvanometer resistor will be equal to voltage across shunt resistor, which means
${i_G}G = S(i - {i_G})$
$ \Rightarrow S = \dfrac{{{i_G}G}}{{i - {i_G}}}$
Range of ammeters can be increased if total current passing through ammeter $'i'$ is increased. Which in turn results in decrease of shunt resistance. Since shunt and galvanometer resistors are in parallel then ammeter resistance also will decrease.
So higher the range less the resistance of the ammeter.
To increase the range of ammeters we are adding additional shunt resistance.
So statement 1 is false and statement 2 is true.

Hence option D is the correct answer.

Note:
In case of conversion of galvanometer to ammeter we will attach a shunt resistance in parallel to galvanometer to get the small resistance ammeter and we will connect that ammeter in series with the circuit where we should measure the current where as if we connect external high resistance in series with galvanometer to make high resistance voltmeter and we connect that voltmeter in parallel to the circuit where we want to measure the voltage.