(20 12? Nantong) In the circuit diagram as shown in the figure, R0 is a constant resistance and R' is a resistance box. First, set the switch S to contact 1, and adjust the resistance value of the res

(20 12? Nantong) In the circuit diagram as shown in the figure, R0 is a constant resistance and R' is a resistance box. First, set the switch S to contact 1, and adjust the resistance value of the resistor box R'=20. (1) When the switch S is turned to the contact 1, the circuit is a simple circuit of the resistance box, and the current in the circuit is measured with an ammeter.

According to ohm's law, the voltage of the power supply is:

u = I 1R′= 0.3a×20ω= 6V；

(2) When the switch S is turned to contact 2, the constant value resistor R0 is connected in series with the resistance box, and the ammeter measures the current in the circuit.

Total resistance in the circuit:

R = UI2 = 6V0.2A = 30Ω，

The total resistance in a series circuit is equal to the sum of the individual resistances.

∴r0=r-r′=30ω-20ω= 10ω；

(3) When the switch S is set to contact 2, the power consumed by the constant value resistor R0 is:

P0 = i22r 0 =(0.2A)2× 10ω= 0.4w。

Answer: (1) The power supply voltage is 6V;

(2) The resistance of the constant value resistor R0 is10Ω;

(3) When the switch S is set to contact 2, the power consumed by the constant resistor R0 is 0.4W 。