# Electricity ```Electricity
CHAPTER 6
Structure of Atoms

Atoms are made of 3 particles

Protons-Positively charges


Neutrons-No Charge


Found in Nucleus
Electrons-Negatively Charged


Found in Nucleus
Found outside of Nucleus
Most of the time, Protons=Electrons

Electrically Neutral
Charged Atoms

When an atom gains or loses and electron, it becomes charged

Called an ion

Atoms cannot lose a proton and remain the same element



1 proton=Hydrogen

3 protons=Lithium

Etc. See Periodic table

The number of protons is called the atomic number
Charges can be confusing…

When an atom GAINS an electron, it becomes negatively charged


Electrons are negatively charged
If it loses an electron, it becomes positively charged


Protons are what determines what element an atom is.
More protons than electrons=more positive than negative
Charge is measured in Coulombs (C)
Static Electricity

Accumulation of excess charge on an object

Gained excess electrons

Shoes on carpet, hair on balloon, cloths in dryer

Because the object is negatively charged, it is attracted
to objects with a positive charge

Opposite charges attract
Law of Conservation of Charge

Yep, another one…

Charge can be transferred, but it cannot be created or destroyed

Typically, it is electrons transferred, not protons
Charges Exert Forces

Unlike charges attract, like charges repel

The force depends on the distance and charge

Called Coulomb’s Law
Charges also create a field

Electric Field-area around charged particles that create a force

Indicated by arrows

Towards negative

Away from Positive
Strength of Electric Force

Electric force is stronger than gravitational force

Why don’t we feel it?

Most objects are electrically neutral
Conductors and Insulators

Conductor-allows electrons to easily pass


Best conductors are metal
Insulator-does not allow electrons to easily pass through

Plastics are great insulators
Charging

Charging by contact

Charged by touching or rubbing

Charging by Induction

Charged by nearby charged
object

Does not need to touch object
Lightning

Storm clouds are arranged with negative charge on bottom

Becomes more negative than objects on Earth’s surface


Static discharges from cloud to surface
http://www.regentsprep.org/Regents/physics/phys03/alightnin/default.htm
Grounding

Connecting an object to Earth with a conductor

Reroutes lightning and electricity

Safety measure
Electric Current
6.2
Current and Voltage Difference

Electric Current-The net movement of electric charge in a single
direction.

Measured in Amperes (A)


If there is no current, there is no NET movement


One Ampere is equal to 1 coulomb per second
Movement forward=movement backward=movement side-to-side
When an electric current is applied, there is still backward and
forward movement, but the electrons drift in the direction of the
current.

Net movement
Before Current is Applied
After Current is Applied
Current and Voltage Difference


Related to the force that causes electric charges to flow.

From area of high voltage to low voltage

Measured in volts (V)
Electric Circuits

A closed path that electric current follows


Battery, wire, lightbulb
Current and electron flow

For historical reasons, we think of current as flow of positive charges

Positive charges do not flow

Due to this, current is in the opposite direction of electron flow

Electrons flow from lower to higher voltage

Current is from higher to lower voltage
Batteries

2 Main Types:

Dry-cell

Wet-cell
Dry-Cell Batteries

Carbon Rod (positive)

Zinc Container (negative)

Moist paste (electrolyte)

Allows electrons to flow

Batteries in flashlights

Metals can be different

Lithium, carbon, and lithium
solution

Cell phone battery
Wet-cell Battery


different metals in an electrolyte

Unlike the paste in dry-cells, the
wet-cell has a liquid

Has many cells connected
together.

acid solution
Electrical Outlets

The 2 holes of an outlet have a voltage difference

In the U.S. usually 120 V
Resistance

Tendency of object to resist flow of electrons


Measured in ohms (Ω)


Takes some of the flowing electrons from the current
This symbol is the capital form of the Greek letter “Omega”
This is why batteries charging get warm

The resistor is taking some of the electrons, and converts the chemical
energy to thermal energy
Ohm’s Law

Current(A)=Voltage difference(V)/resistance(Ω)


𝐼=

Current is measured in Amps (A)
𝑉
𝑅
Where I is current
Example Problem

The voltage difference in a graphing calculator is 6V, and the resistance is
1,200 Ω. What is the current through the batteries of the graphing
calculator?

Knowns: V=6V, R=1200 Ω

Unknown: I=?

Equation: 𝐼 = 𝑅

Solve: 𝐼 = 𝑅 = 1200Ω

=0.005 A
𝑉
𝑉
6𝑉
Equations

Solve for V

Solve for R
Guided Practice

An object has a resistance of 60 Ω as a current
of 2 A goes through it. What is the voltage
difference across the object?
You Try It!

The voltage in a device is 50 V, and the resistance is 5 Ω. What is the current
in the device?
Types of Current



Alternating Current (AC)

Type found in household electrical outlets

Changes direction
Direct Current (DC)

Found in battery-powered devices

Does not change direction
Converters change types (ACDC)
Circuits
6.3
Series Circuits

Electric circuit with only one branch.

Used in things such as flashlights and lamps

Amount of current is the same in all parts

If a part is disconnected, the circuit is broken


Light doesn’t light up
Open circuits

If part of the circuit is removed, the circuit is open

Current does not flow, and object does not work
Parallel Circuits

Circuits that have 2 or more branches

Current can go through any number of the branches

You can turn lights off in one room, and not kill power for whole house


Circuit breakers protect against overheating wires


Used in homes for this reason
Flips open if the wire gets too hot, stopping the circuit
Fuses do a similar thing

Fuses contain a metal that melts if too much current passes through
Electrical Power and Energy

Electrical Power=Rate at which electrical energy is converted to
another form

P=IV

Electrical Power (W)=current(A) x voltage difference (V)

Measured in kilowatts (kW)

1kW=1000W
Example Problem

The current in a cloths dryer is 15 A when it is plugged into a 240 V
outlet. What is the power of the cloths dryer? Answer in kW.

K: I=15A
V=240V

U: P=?

E: P=IV

P=IV=(15A)(240V)

=3600W

=3.6kW
Guided Practice

If a blender is plugged into a 120 V outlet that supplies 2 A of
current, what amount of power is used by the blender?
You Try It!

If a clock expends 3 W of power from a 1.5 V battery, what amount
of current is supplying the clock?
Calculating Electrical Energy

E=Pt


Electrical energy (kWh)=electrical power (kW) x time (h)
To figure out cost for electricity, Power Companies, such as Xcel,
multiply kWh by cost per kWh.

Currently the average in the U.S. is \$0.10 per kWh.

Mine was \$0.07 per kWh last month.
Example Problem

A microwave with a power rating of 1200 W is used for 15 minutes.
How much electrical energy did the power company provide for
the microwave?

K: P=1200W
t=15 minutes

U: E=?

Need to convert!

P=1200W (1kW/1000W)=1.2kW

T=15 m (1hr/60min)=0.25h

E=

(1.2kW)(.25h)=0.3kWh
Guided Practice

A TV plugged into a standard U.S, outlet has a current of 10 A
through it. If a football game took 3 hours, how much did the game
cost to watch assuming the electric company charges \$0.10 per
kWh?
You Try it!

A current of 15 A runs through an appliance with resistance of 3Ω.
The appliance runs 24 hours a day. If the cost per kWh is \$0.10, what
is the daily cost to run the appliance?
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