A moving coil galvanometer with an internal resistance of 5 Ω has a full scale deflection when a current of 20 mA passes through it. Calculate the value of a resistor that will enable it to read 10 A at full scale deflection.

Internal resistance of the galvanometer, $R_g = 5 \, \Omega$.
Full-scale deflection current of the galvanometer, $I_g = 20 \, \text{mA} = 20 \times 10^{-3} \, \text{A} = 0.02 \, \text{A}$.
Desired full-scale deflection current for the ammeter, $I = 10 \, \text{A}$.

To convert a galvanometer into an ammeter, a low resistance (shunt resistor, $R_{sh}$) is connected in parallel with the galvanometer. The total current $I$ splits between the galvanometer ($I_g$) and the shunt ($I_{sh}$).

The voltage across the galvanometer ($V_g$) must be equal to the voltage across the shunt resistor ($V_{sh}$).

Using Ohm's Law ($V = IR$):

The value of the resistor (shunt) is $\text{0.01002 } \Omega$.