A galvanometer having a coil resistance of $60 \Omega$ shows full scale deflection when a current of 1.0 amp…

A galvanometer having a coil resistance of $60 \Omega$ shows full scale deflection when a current of 1.0 amp passes through it. It can be converted into an ammeter to read currents upto $5.0 \mathrm{amp}$ by :
  1. Putting in parallel a resistance of $15 \Omega$
  2. Putting in parallel a resistance of $240 \Omega$
  3. Putting in series a resistance of $15 \Omega$
  4. Putting in series a resistance of $240 \Omega$

Solution

$\begin{aligned} \mathrm{Ig} & =1.0 \mathrm{~A}, \mathrm{G}=60 \mathrm{q}, \mathrm{I}=5.0 \mathrm{~A} \\ \mathrm{~S} & =\frac{\mathrm{I}_{\mathrm{g}}}{\mathrm{I}-\mathrm{I}_{\mathrm{g}}} \mathrm{G} \\ \mathrm{G} & =\frac{1.0}{5.0-1.0} \times 60 \\ & =15 \Omega \text { in parallel } \end{aligned}$

Asked in: NEET 2009 (Mains)

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