Electric Current and

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15 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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Electric Current and
Resistance

Chapter 19 Sections 1 & 2

Current


Current



The rate at which electric
charges move through a given area.


Units for current is called, “Amperes”


A


Amps


1 Amp = 1 Coulomb of Charge per Second

Current vs. Voltage


Current is the flow of electrons through a
conducting material.


Voltage is the pressure in the conducting
material that pushes the electrons.


Voltage can exist without current.


Current can not exist with out voltage.

Electrical Current

𝐼
=





𝐼
=
𝐶 𝑒


=
𝐶ℎ𝑎 𝑔𝑒


=
𝑇𝑖𝑒


Batteries


Batteries act as pumps that push charge
through a conducting material to create a
current.


Batteries do no create charge!


Turn chemical energy into electrical
energy.


Electrical energy is consumed when used,
not charge.

AC vs. DC Current


Direct current is when charges move in
only one direction.


Batteries


Alternating current is when the terminals of
potential difference are constantly
changing sign. Hence there is no net
motion of the charge.


Charges vibrate back and forth


Power lines

Resistance


Resistance



Ratio of the potential
difference across a conductor to the
current it carries.


Units for resistance is an, “Ohm”


Greek Letter Omega “
Ω



Example:


R = 34
Ω

(34 ohms)

Resisting the Flow or Charge


Resistance in the flow of charge can be
related to friction of a moving object.


The resistance holds back the electrons
from flowing freely through the conductor.


Heat is formed as a result.

Applications of Resistors


Resistors are used to control the amount
of current in a conductor.


They do not change the potential difference
(voltage)


They are used in mostly all electrical
devices from televisions to microchips.

Factors That Affect Resistance


Length


The longer the conductor, the more resistance to the
flow of charge.


Cross
-
Sectional Area


The smaller the cross
-
sectional area of the conductor,
the more resistance.


Material


Some objects allow the flow of charge more easily
then others.


Iron has more resistance then copper.


Temperature


The warmer the conductor, the more resistance

Ohm’s Law

𝑉
=
𝐼


𝑉
=
𝑉 𝑎𝑔𝑒

𝐼
=
𝐶 𝑒


=
𝑒𝑖𝑎𝑐𝑒



Ohm’s Law states that voltage, current
and resistance all affect one another.

Superconductors


Superconductors



A material whose
resistance is zero at or below some critical
temperature, which varies with each
material.


By decreasing the temperature of a
conductor, the resistance to the flow of
charge also decrease.