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In the circuit shown in the figure, the power supply voltage is 3V, the resistance R1 is 10ohm, and the resistance is 5ohm. After the switch is closed, what is the connection mode between R1 and R2
As shown in the figure:
After the switch is closed, R1 and R2 are connected in parallel
The voltmeter is connected in parallel with R2, R2 is connected in series with R1, and the ammeter measures the voltage of R1
R1 = 30 Ω, R2 resistance wire is the longest, R2 voltage is 4.5V, when p is at the midpoint of R2, R2 voltage is 3V (1) power supply voltage (2) total resistance of R2 (3) when p is at two positions, the ammeter shows the number
!!! R1 is 30 ohm
(u-4.5) / 4.5 = R1 / R2 (U-3) / 3 = R1 / (R2 / 2) can be solved by (u-4.5) / (U-3) = 3 / 4, the power supply voltage is: u = 9V, then (u-4.5) / 4.5 = R1 / R2, R2 = R1 * 4.5 / (u-4.5) = 30 * 4.5 / (9-4.5) = 30 Ω P at the maximum resistance of R2, I = 4.5 / r2 = 4.5 / 30 = 0.15A P at the maximum resistance of R2
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