b) Resistors

c) total resistance of two or more resistors connected in series; R = R₁ + R₂ +...

d) total resistance of two or more resistors in parallel; 1/R = 1/R₁ + 1/R₂ +...

in series

each additional resistor
- increases the length of the wire
- increases the total resistance
R = R₁ + R₂ + R₃…

in parallel

each additional resistor
- increases the number of pathways
- increases the total cross-sectional area of the wires
- decreases the total resistance
1/R = 1/R₁ + 1/R₂ + 1/R₃

in series