chapter 20: electric circuits

current (I)

the flow of electric charge from one region to another

I = ΔQ/Δt

units: c/s or A

batteries

• convert chemical energy to electrical energy

• establish electrical potential difference

• establish electric field

EMF (ε)

influence that allows conventional current to flow from low electric potential to high

• not a vector

• not a force

units: volts (V)

drift velocity

the average velocity that charged particles attain from an external electric field

resistance (R)

quantifies how much current flows through that resistor when a given potential difference is applied across it

increases by:

• using viscous liquid

• squeezing hose

• making the hose longer

I = V/R

units: V/A

ohm’s law

an ohmic resistor’s resistance does NOT depend on the potential difference applied across it

V = IR

resistivity (ρ)

represent’s fluids viscosity

resistivity & temperature

are directly proportional

ρ(T) = ρ₀[1 + α(T-T₀)]

internal resistance (r)

measured voltage between terminals is smaller than its reported EMF when current is flowing through a battery

power (P)

energy dissipated or absorbed per unit of time

P = IV = I²R = V²/R

series

connected when there is only one conducting path between them (same current flows through)

R_eq = R₁+R₂+R₃…

equivalent resistance

single resistor’s resistance is equal to specific value

parallel

connected when a single path branches into multiple paths (same potential difference across)

1/R_eq= 1/R₁+1/R₂+1/R₃…

kirchoff’s rules

allow solving for properties of a circut when too complicated to R_eq

junction

a point where three or more wires meet

Σ_i I_i = 0

loop

a closed conducting path (ends at the starting point)

Σ_i V_i = 0

ideal voltmeter

has infinite resistance and should be connected in parallel with the measured circuit component

ideal ammeter

has zero resistance and should be connected in series with the measured circuit component

capacitors in series

Q_eq = Q₁ = Q₂

V_ab = V₁+V₂

1/C_eq = 1/C₁+1/C₂+1/C₃

capacitors in parallel

Q_eq= Q₁+ Q₂

V_ab = V₁ = V₂

C_eq= C₁+C₂+C₃

grounding wire

connects an electrical appliance’s conductive case to a metallic rod/pipe in the ground

• creates less resistive path for stray charges to travel to the ground