Solved: PHYSICS Question for NEET

NEET PHYSICSEasy

A galvanometer having a coil resistance of 60 $\Omega$ shows full scale deflection when a current of 1.0 A passes through it. It can be converted into an ammeter to read currents upto 5.0 A by

putting in series resistance of 240 $\Omega$

putting in parallel resistance of 240 $\Omega$

putting in series resistance of 15 $\Omega$

putting in parallel resistance of 15 $\Omega$

Step-by-Step Solution

Concept: To convert a galvanometer into an ammeter (which measures larger currents), a low resistance called a shunt ( $S$ ) must be connected in parallel with the galvanometer coil. This allows the excess current to bypass the sensitive coil .
Formula: Since the galvanometer and shunt are in parallel, the potential difference across them is the same: $I_g G = (I - I_g) S$ Where:

$I_g$ is the full-scale deflection current ( $1.0 \text{ A}$ ).
$G$ is the galvanometer resistance ( $60 \Omega$ ).
$I$ is the total current to be measured ( $5.0 \text{ A}$ ).
$S$ is the required shunt resistance.

Calculation: Rearranging the formula to solve for $S$ : $S = \frac{I_g G}{I - I_g}$ $S = \frac{1.0 \times 60}{5.0 - 1.0}$ $S = \frac{60}{4} = 15 \Omega$
Conclusion: A resistance of $15 \Omega$ must be connected in parallel .

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