A 10 Ω resistor sits alone in a circuit. Now a 40 Ω resistor is wired in parallel with it. That adds more resistor to the circuit. Does the circuit resist the current more now, or less?
Together, the 10 Ω and 40 Ω resistors behave as one unit with a single resistance. The surprise is its size. Measured together, the pair resists less than 10 Ω.
The resistance a parallel pair presents as one unit is called its combined resistance.
So 10 Ω and 40 Ω in parallel combine to less than 10 Ω. That is less than the smaller resistor would resist on its own.
Resistors of 25 Ω and 100 Ω sit in parallel. Their combined resistance is...
Careful with the trap: adding a parallel branch does not raise the circuit's resistance, even though there is more resistor in it. It lowers the resistance.
Caleb wires a second resistor in parallel with the first and says the circuit's resistance must rise, because there is more resistor. Compared with before, the combined resistance is...
A 20 Ω resistor and a 30 Ω resistor sit in parallel. What can you say about their combined resistance?
The combined resistance of resistors in parallel is less than the resistance of the smallest branch.
The smallest branch here is 20 Ω.
The combined resistance is less than 20 Ω.
A 60 Ω resistor is wired in parallel with a 12 Ω resistor. Is the combined resistance more or less than 12 Ω?
The combined resistance of resistors in parallel is less than the resistance of the smallest branch.
The smallest branch here is 12 Ω. The 60 Ω resistor cannot bring the combination above it.
The combined resistance is less than 12 Ω.
A 30 Ω resistor and a 60 Ω resistor sit in parallel. Which of these is their combined resistance?
Compare the two circuit types. In a series circuit, resistances add, so the total is bigger than the biggest. In a parallel circuit, the combination is smaller than the smallest.
A 50 Ω resistor and a 200 Ω resistor sit in parallel. Which of these is their combined resistance?
Two equal 60 Ω resistors sit in parallel. Their combined resistance is...
A third branch is added to a two-branch parallel circuit. The combined resistance becomes...