The electromotive force and internal resistance of three dry cells in series (electromotive force of each cell is about 1.5V and internal resistance is about 0.3 Ohm) shall be measured with ammeter and voltmeter, A ammeter: range 0.6 a, internal resistance 1 ohm. B ammeter: range 3 A, internal resistance 0.2 ohm. C voltmeter: range 3 V, internal resistance 30 Ka ohm. D voltmeter: range 6 V, internal resistance 60 Ka ohm. E sliding rheostat 0 ~ 1000 ohm, rated current 0.1 A. f sliding rheostat 0 ~ 20 ohm, rated current 2 A. g wire key ······Why choose d instead of C voltmeter? Why should the ammeter in the experimental circuit be connected internally instead of externally? Should the ammeter be connected internally when measuring electromotive force?

The electromotive force and internal resistance of three dry cells in series (electromotive force of each cell is about 1.5V and internal resistance is about 0.3 Ohm) shall be measured with ammeter and voltmeter, A ammeter: range 0.6 a, internal resistance 1 ohm. B ammeter: range 3 A, internal resistance 0.2 ohm. C voltmeter: range 3 V, internal resistance 30 Ka ohm. D voltmeter: range 6 V, internal resistance 60 Ka ohm. E sliding rheostat 0 ~ 1000 ohm, rated current 0.1 A. f sliding rheostat 0 ~ 20 ohm, rated current 2 A. g wire key ······Why choose d instead of C voltmeter? Why should the ammeter in the experimental circuit be connected internally instead of externally? Should the ammeter be connected internally when measuring electromotive force?

First of all, the series voltage of three batteries is 4.5V, and the range of C voltmeter is not enough. The reason why the ammeter is connected internally is that both internal and external connections will produce errors. The internal connection will have shunt, and the measured resistance value is too large. The external connection will divide the voltage, and the measured resistance value is too small. The external connection method is generally used for all the small resistance, and the internal connection method is used for the large resistance

The range of a voltmeter is 3V and the internal resistance is 900ohm. How to connect a 15V voltmeter with a large resistance? How to connect a 0.6A ammeter with a large resistance?

It should be changed into a 15V voltmeter with series resistance R = 900 * 15 / 3-900 = 3600 Ω
It is changed into 0.6A ammeter, and the parallel resistance R = 3 / (0.6-3 / 900) = 5.03 Ω

The range of a voltmeter is 3V, and its internal resistance is 600ohm. If the range is changed to 300V, the additional resistance can be calculated

The range of the voltmeter is proportional to the internal resistance
1. First, calculate the internal resistance per volt: 600 / 3 = 200 ohm
2. Calculate the internal resistance of 300 V: 200 * 300 = 60000 ohm
3. Need to increase series resistance: 60000-600 = 59400 ohm
The additional series resistance is 59400 ohm. If there is no appropriate large resistance, it can be obtained by series parallel connection

Can the new and old dry batteries be used in series or in parallel
Why? Why

It can be connected in series, not in parallel, because the old battery is equivalent to a resistor in series in the circuit. In parallel, the new battery needs to charge the old battery, reduce the voltage, waste electric energy, and can not reach the corresponding application. However, try not to mix the old and new batteries, and the old battery needs to consume a certain amount of electric energy