Battery

Produces constant __voltage__ to make charges move (current)

- Electrons free to move in conductors → carry energy through circuit.
- Energy comes from a battery (converts
**chemical → electrical energy**) - As energy is transformed, a potential difference V develops across the battery’s terminals (called EMF).

Current

amount of charge that passes through an area in a given amount of time

units: Amps → (1A = C/s)

Equations for current (I)

Current in a metal wire is proprotional to what?

Current (I) proportional to potential diff (V) applied to its 2 ends

Electrode

plates/rods (made of dissimilar metals)

Electrolyte

solution (ie a dilute acid)

Terminal (battery)

part of electrode outside of solution (where you connect wires/circuits)

What is the simplest BATTERY made of?

2 electrodes (+ and –) & 1 electrolyte

Ciruit

continuous conducting path connected between terminals of a battery

Complete Circuit

continuous conducting path

Open circuit

break in circuit (ie. cut wire)

Ground

common conductor (provides continuity)

Conventional current

current direction in a circuit = **direction + charge would flow**

Resistance

opposition to flow of charge

units: ohms → (1 Ω = 1 V/A)

In a device that produces heat (ie. toaster) what kind of resistance do you want?

HIGH resistance needed (otherwise no heat produced)

Do you want low/high resistance in wires?

LOW resistance wires (to minimize energy loss)

Resistance of a uniform wire EQUATION

p = constant of proportionality (RESISITIVITY) → units (Ω m) → depends on material used

What is special about silver?

It has the **lowest resistivity (p)**, therefore lowest resistance (R) making it **best conductor** → electrons free to move

Ohm’s Law EQUATION

V = IR

To what materials can Ohm’s law be applied?

Ohmic materials: metal conductors (**R is constant**) whose temperature doesn’t change much

What are **resistors** used for?

used to control (reduce) the amount of current in a circuit

What factors does **resistance** depend on?

type of material wire made of, length, cross sectional area

Electrical conductivity

amount of current a material can carry

(reciprocal of resistivity)

Electrical conductivity EQUATION

How does **temperature** effect **resistance**?

R of metals INCREASES at higher temp

(because atoms move faster and interfere more with flow of electrons)

Power

amount work down / time

rate energy is transformed

Power EQUATIONS

P = IV

P = W/t

Do thicker wires have less or more resistance?

less R

Fuses/circuit breakers

switches that open the circuit when current exceeds a safe value to prevent overloading

Open circuit

no longer a complete conducting path (no current can flow)

as if R = infinity

Short ciruit

two wires touched that shouldn’t have

Q: Why shouldn’t properly rated fuses be replaced by higher-rated ones?

Fuse won’t blow as intended and high current will harm (ie. melt) whole circuit…

Direct Current (DC)

one-directional flow of electric charge

(battery example)

Alternating current

reverse direction many times/sec (sinusoidal)

Rectifier

AC → DC current

Inverter

DC → AC