Hi BvU
The dots are representing the missing "method" to get to the answer.
In task-part a) i came to the result, that i have to add an other resistance Rv with 247,3kOhm in series so that the moving coil movement shows full deflection.
In b) the internal resistance increases by 20% and...
a)
dimension the moving-coil movement so that it indicates full deflection at 25 V
given Values:
Voltage Source: U2Max = 25V;
moving-coil movement: IM = 100µA; UM = 270mV
Rv = ( U2Max - UM ) / IM = (25V - 270mV) / 100 µA = 247,3kΩ
b) the internal resistance is increased by 20 %...