Max photography Nantong

(1) When the switch S 1 is closed and S2 is open, the circuit is a simple circuit of R 1, and the current in the circuit is measured with an ammeter, then

r 1 = ui 1 = 4v 0.25 a = 16ω；

(2) When the switches S 1 and S2 are closed, the two resistors are connected in parallel, and the ammeter measures the main current.

∫ Each branch of parallel circuit works independently and does not affect each other.

∴i2=i-i 1=0.55a-0.25a=0.3a，

w2 = UI2t = 4v×0.3a×60s = 72J；

(3) When the resistance of the sliding rheostat connected to the circuit is maximum and the electric power consumed by the sliding rheostat is minimum, then

p2min = u2r 2 max =(4V)220ω= 0.8W，

When I=0.6A is the maximum indicator of ammeter, the sliding rheostat consumes the largest electric power, then

i2max = I-I 1 = 0.6A-0.25 a = 0.35 a，

p2max = ui 2 max = 4v×0.35 a = 1.4w。

A: The resistance of (1) resistor R 1 is16 Ω;

(2) When the switches S 1 and S2 are closed, the power consumption of the sliding rheostat is within 72J 1 min;

(3) When the switches S 1 and S2 are closed, the maximum power consumption of the sliding rheostat is 1.4W and the minimum power consumption is 0.8W under the condition of ensuring the safety of the ammeter.