One situation where the Voltmeter and Ammeter method would be preferable, would be if the resistance of the components change with the operation of the circuit. The simplest example of this is a light bulb, where the resistance changes with the temperature of the filament. So you would want to see how it is behaving during normal operation.
This may not be the most suitable method because measuring the current using ammeter requires switching off power, introduction of the meter by breaking the circuit at suitable point, power on, then measure the current and finally switching off power, removal of ammeter, re-connection of circuit etc. The preferred method would be to use the modern high impedance ohm meter (of course with the power turned off) without disturbing the circuit.
Voltmeter gives the voltage and ammeter the current.
Using Ohms law, resistance can be found by R = V / i
It is often not possible to accurately measure a resistance in-circuit. You need to open one end of the resistive element to make the measurement.
On the other hand, you can usually measure the voltage across a resistance, and the current can often be determined by measuring other parameters in the circuit (ex - the voltage across a known resistance in series with the unknown). Knowing the voltage and current, you can determine the resistance without removing it from the circuit.
Thevenin's equation says all complex systems can be represented by a thevenin voltage and a thevenin resistance. It is not as simple as applying a voltage and measuring the current, but that is indirectly correct.
In essence any change in voltage can be used to identify the change in current and therefrom estimate the resistance of the circuit be it a biased transistor or any other.
So do study thevenin's equation in detail and you will know the answer. though it is not as simple as you put..
why is the voltmeter - ammeter method is the most suitable method for measuring resistance in complicated networks?
