ELECTRIC CURRENT

Electricity, like water, can only flow if charged particles have potential.

An electron in motion defines an electric current.

e-

In fact, any charged particle that moves defines an electric current.

Na+

A moving sodium ion, for example, defines an electric current

The rate of flow of electric charges is how we measure current

e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-

One coulomb of electric charges per second passing through a conductor is 1 ampere, or 1 “amp”.

1 Coulomb

1.6 x 10-19 C/e-= 6.28 x 1018 electrons

Remember…

So: 1 Coulomb/second = 6.28 x 1018 e-/s

1 amp = 6.28 x 1018 fundamental charges/sec

Current is abbreviated as: I

What is the relationship between potential and flow?

There is a direct relation between potential and flow

So: I V

But, some conductors allow for greater flow than others.

So, the RESISTANCE (R) to flow must also be considered.

We can say that resistance is INVERSELY PROPORTIONAL to flow.

So: I R

1

THEREFORE:

When we put everything together,

RVI

This equation is known as Ohm’s Law

In the world of electricity, the electrical potential is the VOLTAGE (V)

It represents the energy per unit charge.

Remember that 1 Volt = 1 Joule/Coulomb

Unit summary:

coulomb

jouleElectrical potential =

sec

coulombcurrent =

= volt

= amp

So, if RVI then

IVR

R = amp

volt2/

/

C

sJ

C

s

C

J

sC

CJ

This unit is far more commonly known as the OHM

= Ω

RESISTANCE

Depends on three factors:

1.The type of material (ρ)2. The length of the conductor (L)3. The cross-sectional area of the

conductor (A)

RESISTIVITY (ρ)

It varies with temperature

In general, the resistivity INCREASES with increasing temperature

CIRCUITS

In order for electricity to be useful, it must flow in a closed circuit.

The source of potential (voltage) must have a closed pathway for current to flow.

With few exceptions, all circuits have some resistance to current flow.

These symbols are found in your reference tables and provide the standard symbols for circuit components.

These diagrams represent circuits found on Regents Exams.

Can you identify the symbols?

TYPES OF CIRCUITSTYPES OF CIRCUITS

There are two basic types:

Series

Parallel

A series circuit has all of the resistors in line with the conductor

Parallel Circuits

Resistors are arranged in parallel along more than one conductor.

Series or parallel?

Series or parallel?

Note that the ammeter is placed in series

Note that the voltmeter is placed in parallel.