Question

A galvanometer coil has a resistance of 30 ohm and meter shows full scale deflection for a current of 2.0 mA. Calculate the value of resistance required to convert it into an ammeter of range 0 to 1 A.​

Answer 1

★ Given :-

• Resistance of galvanometer = 30 Ω
• Current flowing through the galvanometer = 2.0 mA

★ To find :-

• Convert the galvanometer into an ammeter of range 0 - 1 A

★ Solution :-

• In order to convert a galvanometer into an ammeter a resistor (small resistance ) must be attached in parallel combination with the galvanometer
• This resistor having small resistance is known as a shunt
• Let, us assume that current I is flowing through the galvanometer when no shunt is connected to it
• When a shunt is connected in parallel combination to the galvanometer I - I g current flows through the shunt so that the desired amount of current flows through the galvanometer i.e Ig

We know that ,In parallel combination the potential difference across two resistors is the same

$\implies\mathtt{V_g = V_s }$

$\implies\mathtt{I_g G =( I - I_g) S }$

$\implies\mathtt{0.002\times 30 =( 1 - 0.002) S }$

$\implies\mathtt{0.06 =0.998 \times S }$

$\implies\mathtt{S =\dfrac{0.06}{0.998}}$

$\implies \boxed{\mathtt{S =0.06 \Omega} }$

The value of resistance required to convert it into an ammeter of range 0 to 1 A is 0.06 Ω