Question

Solve each problem. Be sure to show your work and give a final answer with units rounded to the given number of significant figures.

1) Find the voltage on a circuit with a resistance of 12.5 Ω if it has a current of 2.35 A.

2) If a circuit with a 9.0 V battery has a current of 6.2 A, how much resistance is in the circuit?

3) A circuit has three resistors with values of 4.0 Ω, 8.0 Ω, and 12 Ω. What is the equivalent resistance if they are wired in series?

4) A circuit has three resistors with values of 4.0 Ω, 8.0 Ω, and 12 Ω. What is the equivalent resistance if they are wired in parallel?

Answer 1

1. V = i R
2. so R = V/i
3. resistors in series add, same current through each so the iR voltages add
4. In parallel, the currents add for the same voltage on each
so i1 = V/R1 and i2 = V/R2 and i3 = V/R3
so
i = i1 + i2 + i3 = V(1/R1+1/R2+1/R3)
but overall, i = V/Req where Req is the equivalent resistance we want
so
V/Req = V(1/R1+1/R2+1/R3)
Req = 1 / (1/R1 + 1/R2 + 1/R3)

Answer 2

https://www.electronics-tutorials.ws/resistor/res_4.html

Answer 3

Oh, I get. Thank sm, Damon! :)