A PMMC meter has an internal resistance 200 Ω and the current required for its full scale deflection is 50 μA. The meter is capable of measuring on its own a maximum voltage of: 

Ammeter sensitivity:

• Ammeter sensitivity is the amount of current necessary to cause full scale deflection (maximum reading) of the ammeter.
• The smaller the amount of current, the more "sensitive" the ammeter.
• For example, an ammeter with a maximum current reading of 1 mA would be more sensitive than an ammeter with a maximum reading of 1 ampere.

Current sensitivity is given by

    (A-1 or Ω/V)

Where

S = Sensitivity of ammeter.

If = Full scale deflection of an ammeter.

Rint = Internal resistance of an ammeter

Vm = Full range voltage.

Calculation:

Here Rint = 200 Ω, If = 50 μA,

∵  (Ω/V)

 ⇒ Vm = 200 / 20000 ⇒ Vm = 10 mV.