10/3 Circuits

Electric Force

made charges move as a force, but needed to know the amount of charges and their sings

Ohm’s law

V = IR

Not all ___ obey Ohm’s law

Circuits

Circuits that obey Ohm’s Law must have a linear slope when plotting V vs. R. These circuits are called

Ohmic

Current is the 

flow of charge per second 

Variable symbol of Current is

I

SI Unit for current is

ampere (A)

Fundamental units of currents are

Coulombs per second (c/s)

Current only flows when there is a voltage

difference

Voltage difference means there is an 

electric field 

Electric field means there is a net

electric field

Net force means there is a net acceleration on the

moving charge

The charge that moves is the

electron

The actual sideways motion of an electron is

1 mm per second

There are 2 flows of current

Conventional current and Electron current

Conventional current

pretends a positive change carrier (positron-like) (+e) flows through wires

Electron current

the actual current that flows through wires (-e)

There are 2 kinds of current

Alternating current and Direct current

Alternating current (AC) -

current that flows out of our walls. Voltage alternates from +120 V to -120 V with a frequency of 60 Hz

Direct current - 

current that flows out of power bricks, batteries, and most chargers. Voltage is considered constant.

Resistivity

is found in all objects except when hat object is superconductor

A superconductor, by definition, has

zero resistivity

Conductivity is the

reciprocal of resistivity

Resistivity is like the 

difficulty in moving a charge through a material 

Resistivity depends on the material and average internal kinetic energy of that

material

Higher the temperature,

higher the resistivity

Resistance is an

intrinsic property of matter

Resistance is equal to

resistivity times the length of the conductor divided by the cross-sectional area

Resistace is the amount of

resistivity in a volume of material

The bigger the cross-sectional area, the

lower the resistance

the longer the wire, the 

higher the resistance

Voltage sources

add or subtract a potential difference across a circuit (Batteries, wall sockets, and power supplies)

Potential difference is also called the

Electromotive Force

EMF

Potential difference, and change in voltage are synonyms. Technically EMF is only used for any kind of electrical energy

Real voltage sources have

internal resistance that reduces the delivered voltage