Resistance R1 = 7 Ω, R2 = 5 Ω, connected in series at both ends of 12V power supply. At this time, the total resistance of the circuit is_____ Ω, R2 voltage___ 5. In parallel in a 3V circuit, The total resistance after parallel connection is____ Ω, when the current passes through the main road____ A. Comparison of current in R1 and R2____ . [a total of 5 blanks, yes, fill in the blanks = 3 =, no process, no matter]

Resistance R1 = 7 Ω, R2 = 5 Ω, connected in series at both ends of 12V power supply. At this time, the total resistance of the circuit is_____ Ω, R2 voltage___ 5. In parallel in a 3V circuit, The total resistance after parallel connection is____ Ω, when the current passes through the main road____ A. Comparison of current in R1 and R2____ . [a total of 5 blanks, yes, fill in the blanks = 3 =, no process, no matter]

twelve
five
35/12
36/35
5:7

To calculate the resistance, I want to use the 12V of the computer power supply to connect an LED lamp bead. The LED parameter is voltage 3V and current 20mA. How much resistance do you need? Please write the formula together. Thank you

In series circuit, the current is equal, so the resistance current is 20mA
The resistance needs to be divided into 12-3 = 9V
Then r = u / I = 9 / 0.02 = 450 ohm

The resistance of R1 = 6 Ω and R2 are connected in series with a 12V power supply, and the voltage at both ends of R1 is 3V. Find 1. The current in the circuit 2. The voltage at both ends of R2 3. The resistance of R2

Current = u / r = 3 / 6 = 0.5A
Voltage at both ends of R2 = 12-3 = 9V
R2 = 9 / 0.5 = 18 ohm