# When a moving coil galvanometer has a resistance of 20 ohms and gives full-scale deflection of...

## Question:

When a moving coil galvanometer has a resistance of 20 ohms and gives full-scale deflection of 1.5 m. Calculate the potential difference across its terminals when the current is flowing.

## Electric Current

The movement of charged ions from one point to another in a circuit due to the development of potential at the ends in a unit of time is called electric current. The SI unit for indicating the quantity of current is ampere. The galvanometer shows the reading of current in mA.

Given data

• The resistance of the galvanometer is: {eq}{R_G} = 20\;{\rm{ohms}} {/eq}.
• The full scale deflection in galvanometer is: {eq}I = 1.5\;{\rm{mA}} {/eq}.

Note

The deflection shown in galvanometer shows the value of current which is measured in milliAmpere (mA).

The expression for the potential difference when the current is flowing is given as,

{eq}V = I{R_G} {/eq}

Substitute the values in the above equation.

{eq}\begin{align*} V &= 1.5\;{\rm{mA}}\left( {\dfrac{{1\;{\rm{A}}}}{{1000\;{\rm{mA}}}}} \right) \times {\rm{20}}\;{\rm{ohms}}\\ &= {\rm{0}}{\rm{.03}}\;{\rm{V}} \end{align*} {/eq}

Thus, the potential difference across the terminals is {eq}0.03\;{\rm{V}} {/eq}.