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As shown in the figure, the power supply voltage U remains unchanged, and the indication of ammeter is 2A. Resistance R1 and R2 are in parallel, equivalent resistance R, and R1: r = 4:3, If the power consumed by resistor R2 is 2.5W. Find the power supply voltage
2A in this question should be the main current
R2 = 4R can be obtained from R1 = 4R / 3 and 1 / r = 1 / R1 + 1 / R2
Because i-i1 + I2 in parallel, I1 / I2 = R2 / R1, I2 = 0.5A
U = 5V from P = UI
As shown in the figure, t is the ideal transformer, A1 and A2 are the ideal AC ammeters, V1 and V2 are the ideal AC voltmeters, R1, R2 and R3 are the resistors, and the two ends of the original coil are connected with sinusoidal alternating current with a certain voltage. When the switch S is closed, the indication change of each AC ammeter should be ()
A. The reading of voltmeter V1 decreases B. the reading of voltmeter V2 increases C. The reading of ammeter A1 increases D. the reading of ammeter A2 decreases
When the switch S is closed, the total resistance decreases. As the total current increases, the voltage of resistance R1 increases, and the total voltage remains unchanged, the voltage of the parallel part decreases, that is, the reading of V1 decreases, so a is correct
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