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 resistance

R = R₁ + R₂ + R₃…

• total resistance of a series circuit (Ω) = resistance of the first resistor (Ω) + resistance of the second resistor (Ω) + resistance of the third resistor (Ω)…

in parallel

• each additional resistor increases the number of pathways → increases the total cross-sectional area → decreases the resistance

1/R = 1/R₁ + 1/R₂ + 1/R₃

• 1/total resistance of a parallel circuit (Ω) = 1/resistance of the first resistor (Ω) + 1/resistance of the second resistor (Ω) + 1/resistance of the third resistor (Ω)

in series

• ratio of R between two components = ratio of V across two components

  • 2:1 R between two components = 2:1 V across two components

in parallel

• ratio of R between two branches = reverse ratio of I between two branches

  • 2:1 R between two branches = 1:2 I between two branches