Transcript Electric Charge and Static Electricity

Electric Charge and
Static Electricity
20.1
Electric Charge

Electric charge is a property that causes
subatomic particles (protons and electrons) to
attract or repel each other.

There are two types of electric charge:
 Positive (proton)
 Negative (electron)
Electric Charge

An atom is neutral with a positive nucleus and is
surrounded by a negatively charged cloud of
electrons.

An excess or shortage of electrons produces a
net electric charge (ion).

The SI unit of electric charge is the coulomb (C)
Recap of the Atom
Electric Forces

Like charges repel, and opposite charges attract.

The attraction or repulsion between electrically
charged objects is electric force.

EX: balloon and hair
Electric Forces

The electric force between two objects is directly
proportional to the net charge on each object
and inversely proportional to the square of the
distance between them.

aka the larger the charge, the larger the electric
force. The larger the distance, the smaller the
electric force.
Electric Forces

Inside an atom, electric forces are much stronger
than gravitational forces.
Electric Fields

The effect an electric charge has on other
charges in the space around it is the charge’s
electric field.

The strength of an electric field depends on the
amount of charge that produces the field and on
the distance from the charge.
Electric Field

The lines representing the field are closer
together near the charge, where the field is
stronger.
Field of a Positive and Negative
Charge
Static Electricity and Charging

Static electricity is the study of the behavior of
electric charges, including how charge is
transferred between objects.

Charge can be transferred by friction, contact
(conduction), and induction.
Static Electricity and Charging

The law of conservation of charge states that the
total charge is the same before and after the
transfer occurs.
Charging by Friction

Rubbing two objects together causes friction,
which causes a transfer of electrons.
Charging by Contact

Whenever two objects touch (not rubbed
together) and charge is transferred.
Charging by Induction

A transfer of charge without contact between
materials.

EX: walking across carpet and then touching a
door knob.
Static Discharge

Static discharge occurs when a pathway through
which charges can move forms suddenly.

Charges will not travel through air from your
hand to the doorknob. The air becomes charges
suddenly when the gap between your finger and
the doorknob is small. This air provides a path
for electrons to flow from your hand to the
doorknob.
Electric Current and
Ohm’s Law
20.2
Electric Current

The continuous flow of electric charge is an
electric current.

The SI unit of electric current is the ampere (A),
or amp, which equals 1 coulomb per second.

The two types of current are direct current and
alternating current.
Electric Current
Direct current (DC) is where charge only flows in
one direction.

Alternating current (AC) is a flow of electric
charge that regularly reverses its direction.

Current is the direction in which positive
charges flow.
Direct Current
Conductors and Insulators

An electrical conductor is a material through
which charge can flow easily.
 EX: copper and silver

A material through which charge cannot flow
easily is called an electrical insulator.
 EX: wood, plastic, rubber, and air
Resistance

Resistance (R) is opposition to the flow of
charges in a material.

The SI unit of resistance is the ohm.
Resistance

A material’s thickness, length, and temperature
affect its resistance.

A superconductor is a material that has almost
zero resistance when it is cooled to low
temperatures.
Voltage

In order for charge to flow in a conducting wire,
the wire must be connected in a complete loop
that includes a source of electrical energy.

Potential difference is the difference in electrical
potential energy between two places in an
electric field.
Voltage

Potential difference is also called voltage (V).

Three common voltage sources are batteries,
solar cells, and generators.

A battery is a device that converts chemical
energy to electrical energy.
Ohm’s Law

Ohm’s Law states that the voltage (V) in a
circuit equals the product of the current (I) and
the resistance (R):

V=IxR

Increasing the voltage increases the current.
Keeping the same voltage and increasing the
resistance decreases the current.
Ohm’s Law Practice

What is the voltage if the resistance is 3 ohms
and the current is 3 amps?

V=IxR