[emergency] in the circuit shown in the figure, the voltage of the power supply is u, R is the constant resistance, the range of the voltmeter is 0 ~ 15V, and the range of the ammeter is 0 ~ 0.6A, Adjust the sliding rheostat, when voltage U1 = 12V, current I1 = 0.25A, when voltage U2 = 7.2V, current I2 = 0.4A 1. Power supply voltage U; 2. Resistance value of resistance R 3. In order to ensure the safety of the circuit, the sliding rheostat is connected to the resistance range of the circuit

[emergency] in the circuit shown in the figure, the voltage of the power supply is u, R is the constant resistance, the range of the voltmeter is 0 ~ 15V, and the range of the ammeter is 0 ~ 0.6A, Adjust the sliding rheostat, when voltage U1 = 12V, current I1 = 0.25A, when voltage U2 = 7.2V, current I2 = 0.4A 1. Power supply voltage U; 2. Resistance value of resistance R 3. In order to ensure the safety of the circuit, the sliding rheostat is connected to the resistance range of the circuit

1. Let the power supply voltage be u, and use Ohm's Law: (u-u1) / r = 0.25 (u-u2) / r = 0.4 algebra to get: (U-12) / r = 0.25 (u-7.2) / r = 0.4 two formulas are compared to get: (U-12) / (u-7.2) = 0.25 / 0.4 solution: u = 20v2, substituting u = 20V into (U-12) / r = 0.25 has: 8 / r = 0.25r = 32

Power supply voltage = 9V, R1 = 3 ohm, R2 range 0-20 ohm, ammeter 0-0.6a, voltmeter 0-3v, calculate the value range of sliding rheostat R2
How to choose the range of voltmeter and ammeter and the resistance value of sliding rheostat for the experiment problem which has given experimental equipment for choice?

9 / 0.6 = 15 Ω, 15-3 = 12 Ω, that is, R2 value range is 12-20 Ω, too small will burn the ammeter

As shown in the figure, the power supply voltage is 9V, R1 = 3 Ω, and the variation range of sliding rheostat R2 is 0 ~ 20 Ω. If the ammeter adopts the range of 0 ~ 0.6A, and the voltmeter adopts the range of 0 ~ 3V, in order not to damage the ammeter and voltmeter, the value range of sliding rheostat R2 is calculated

It can be seen from the circuit diagram that the setting resistor R1 is connected in series with the sliding rheostat R2, the voltmeter measures the voltage at both ends of R1, and the ammeter measures the current in the circuit; according to the requirements: I ≤ 0.6A, when I = 0.6A, U1 = IR1 = 0.6A × 3 Ω = 1.8V, the voltmeter will not exceed the range, ∵ the total voltage in the series circuit is equal to the sum of the partial voltages, ∵ U2 = u-u1 = 9v-1.8v = 7.2V, according to Ohm's law, the sliding rheostat is connected The minimum value of the circuit: r2min = u2i = 7.2v0.6a = 12 Ω, sliding rheostat connected resistance range: 12 Ω ~ 20 Ω. Answer: the value range of sliding rheostat R2 is 12 Ω ~ 20 Ω

The power supply voltage is 9V, the indication of ammeter is 0.6A, and the indication of voltmeter is 3V. Calculate the value of sliding rheostat connected into the circuit

What voltage does the voltmeter measure?
If the voltage of sliding rheostat is measured, the resistance connected to the circuit is 3 / 0.6 = 5 Ω;
If the total voltage of the circuit resistance is measured, the resistance value connected to the circuit is (9-3) / 0.6 = 10 Ω
These are the two simplest topics, and we should deal with them in a specific way