Why internal resistance of ammeter is zero and internal resistance of voltmeter is high?
Answers
Since an Ammeter is connected is connected in series , So in order to minimize any voltage drop across the ammeter that may leads to deduction in source voltage there by reducing the current in the main component, the resistance of an ammeter is practically zero.
I = V/(R + Rₐ)
So if the resistance of ammeter is high the whole current in the circuit is reduced.Hence it is kept as low as possible.
Since a voltmeter is connected in parallel , So in order to reduce any current flow diverted to voltmeter that may leads to deduction of current capacity of source thereby reducing the voltage of the main component, the internal resistance of voltmeter is kept very high.
V₁ = V x R/(RIIRv) = V x Rv/(R+Rv)
Hence if the voltmeter resistance is low then the voltage across the main component would decrease, Hence it is kept as high as possible.