Transcript Electricity & Magetism

Electricity & Magnetism
Ch 9
6th grade
How do charges interact?
• Atoms contain charged particles called
electrons (-) and protons (+).
• If two electrons come close together, they
repel each other. Protons act the same
way.
• If a proton and an electron come together,
they attract one another because the two
have opposite electric charges.
• The interaction between electric charges is
called electricity.
• The force between charged objects is
called electric force.
• An electrical field is a region around a
charged object where the object’s electric
force is exerted on other charged objects.
Electric Fields
• Electrical fields and forces get weaker the
farther away from the charge.
• An electrical field is invisible.
• Field lines point away from positive
charges and toward negative charges.
• Single charges have straight field lines,
but if multiple charges are present, these
forces combine to make more complicated
field lines.
How does charge build up?
• Most objects have no charge because
each atom’s positive charge is balanced
by a negative charge.
• An uncharged object can become charged
by gaining or losing electrons
– If it looses electrons, it will have an overall
negative charge.
– If it gains electrons, it will have an overall
positive charge.
Static electricity
• This build up is called static electricity.
• Charges build up on an object, but they do
not flow continuously.
• Charges are neither created nor
destroyed. This is known as the law of
conservation of charge.
• If one object loses electrons, another
object must pick them up.
Methods
• Friction: uncharged objects are rubbed
together and moves electrons from one to the
other
• Conduction: charged object touches another
object and transfers electrons
• Induction: reaction to the electric field of a
charged object without touching the object*
• Polarization: electrons react to electric fields
resulting in individual atoms having charged
ends that are attracted to charged objects*
• *parts of objects end up charged
Static discharge
• Positively charged objects gradually gain
electrons and negatively charged
gradually loose electrons and the objects
eventually become neutral.
• Objects hold on to charge better in dry air.
• Lightening bolts are also discharge from
the charge that builds up within the clouds.
Electric current
• Static electric charges do not flow
continuously, but when electric charges
are made to flow through a material, they
produce an electric current.
• The amount of charges that passes
through a wire in a given period of time is
the rate of electric current, called an
ampere, or amp (A).
Circuit
• In order to maintain an electric current,
charges must be able to flow continuously
in a loop, called an electric circuit.
How do conductors differ from
insulators?
• The atoms in conductors have loosely
bound electrons that can move freely.
• Electrons in insulators cannot move freely
among atoms.
What affects current flow?
• Current flow is affected by the energy of the
charges and the properties of the objects that
the charges flow through.
• Electric currents flow through wires like water
through pipes and changes into different
forms of energy.
• Voltage is the difference in electric potential
energy per charge between two points in a
circuit.
• The amount of current in a circuit also
depends on the resistance of the circuit.
• The greater the resistance, the less
current there is for a given voltage.
• The unit of measure of resistance is the
ohm (Ω)
Factors that determine resistance
• Diameter: Current flows more easily through
a wide wire than through a narrow wire.
• Length: Short wires have less resistance than
long wires.
• Material: Electrons loosely held to their atoms
have a low resistance.
• Temperature: The electrical resistance of
most materials increases as temperature
increases.