Transcript Electricity Notes Ch. 6

Chapter 6
Electricity
Section 1: Electric Charge and Static
Electricity
• A force is a push or pull exerted on an object.
• Energy is the ability to do work or cause
change.
• Potential energy is the stored energy that
results from the position or shape of an
object.
Key Concepts
• 1. Charges that are the same repel each
other. Charges that are different attract each
other.
• 2. There are 4 methods by which charges can
redistribute themselves to build up static
electricity: by friction, by conduction, by
induction, and by polarization.
How do charges interact?
Atoms contain charged particles called
electrons and protons. The charge on a
proton is positive (+). The charge on an
electron is negative (-).
If 2 electrons or 2 protons come closer
together, they push each other apart. If a
proton and an electron come close together,
they attract one another because they have
opposite electric charges.
* The interaction between electric charges is
called electricity.
* The force between charged objects is
called electric force.
* An electric field is a region around a
charged object where the object’s electric
force is exerted on other charged objects.
* Electric fields and forces get weaker the
farther away they are from the charge.
How does charge build up?
•The buildup of charges on an object is called
static electricity. In static electricity, charges
build up on an object, but they do not flow
continuously.
•Law of Conservation of Charge: Charges are
neither created nor destroyed. An object
cannot become charged by destroying or
creating its own electrons. If one object loses
electrons, another object must pick them up.
4 ways to build up static electricity:
1. By friction- the transfer of electrons from one
uncharged object to another by rubbing the
objects together.
2. By conduction- the transfer of electrons from
one object to another by direct contact.
3. By induction - electrons react to the electric
field of a charged object without touching the
object itself.
4. By polarization – electrons move within their
own atoms because of an external electric field.
Static discharge results in the loss of static
electricity as electric charges transfer from
one object to another. A spark is often
produced. Lightning bolts are examples of
static discharge.
Section 2: Electric Current
1. When electric charges are made to flow through a
material, they produce an electric current.
2. The unit for the rate of electric current is the
ampere (amp) or A. The number of amps
describes the amount of charge flowing past a
given point per second.
3. A complete, unbroken path that charges can flow
through is an electric circuit.
Conductors and Insulators
1. A conductor allows electrons to flow easily through it
(are loosely bound);metals are good conductors
2. Insulators do not allow electrons to flow easily;
electrons cannot move freely.
3. Current flow is affected by the energy of the charges
and the properties of the objects that the charges
flow through. Circuits convert electric potential energy
into light and heat.
Voltage (V) is the difference in electric potential energy
per charge between 2 points in a circuit.
Resistance measures how difficult it is for charges to
flow through the object. The greater the resistance,
the less current there is for a given voltage. The ohm
(Ω) is the unit of measure for resistance.
4 factors determining resistance: diameter, length,
material, and temperature.
Current will always take the path of least resistance.
Section 3: Electric Circuits
Ohm’s Law:
Resistance = Voltage
Current
Ohms (Ω) = volts (V) ÷ amps (A )
One ohm = one volt per amp
Voltage = Current · Resistance
All electric circuits have:
1) Devices that run on electrical energy
2) Sources of electrical energy
3) Conducting wires
Energy is always conserved in a circuit; it will be
transformed into heat, light, sound, or mechanical
energy.
Circuits usually have a switch to control the
current.
A series
circuit
has only
one path
for the
current
to take.
Disadvantages of series circuit:
1. If one light goes out, all the others do also.
2. Light bulbs become dimmer as more are
added to the series.
Parallel Circuit: There are several paths for the
current to take. Advantage: if one bulb burns
out, the others will stay lit. Overall resistance
decreases, do bulbs do not grow dim as more
are added to the circuit.
Section 4: Electric Power and Safety
Power: the rate at which energy is transformed from
one form to another; the unit of power is the WATT
Power = Voltage ∙ Current
Units: watts (W) = volts (V) ∙ amperes(A)
You can rearrange the equation do it reads:
Current = Power
Voltage
***See page 183 for problems***
Energy = Power ∙ Time
* Electric power is measured in kilowatts (kW);
time measured in hours, so electrical energy
often is measured in kilowatt-hours (kWh).
Shocks can be prevented by the third prong on
plugs (connects to house’s ground wire), circuit
breakers, and fuses. These things either
redirect current or break circuits.