Electrity Flashcards
Electricity
- form of energy
- results from interaction
of charged particles
(e.g. –ve electrons or
+ve protons)
STATIC CHARGE (STATIC ELECTICITY)
- tends to stay on the surface of an object
rather than flowing away quickly. - ‘static’ = stationary
Clothes in a dryer build up a static charge when
they rub together and are charged by friction.
CHARGING BY FRICTION
- objects made from different materials rub
against each other, producing a net charge
(+ve or –ve) on each object. - e.g. rubbing a rubber balloon against a sweater
– e.g. combing your hair with a plastic comb
Causes of Electric Charges
In the image below, electrons are transferred from the hair
to the comb. The hair is left with an excess of protons (or a
shortage of electrons) resulting in a positive charge, and
the comb is left with an excess of electrons, resulting in a
negative charge.
Only electrons are transferred between the hair and comb.
Protons and neutrons cannot leave the nucleus of the atom.
(Page 404)
- e.g.
– hair is combed (charging by friction)
– comb has a stronger attraction for electrons than hair
– comb pulls electrons off the hair – i.e. electrons are
transferred from hair to comb
– both materials become charged due to an excess or
deficit of electrons - hair ends up with a positive charge
- comb ends up with a negative charge
Causes of Electric Charge
- movement of
electrons! - why electrons?
– because they have a
small mass and are
further from the
nucleus.
Electrostatic series
- is a list of materials arranged
according to their ability to hold
onto electrons. - when a material higher on the list
is rubbed with a material lower
on the list, it loses electrons and
becomes positively charged. - the material that gained the
electrons becomes negatively
charged.
INSULATOR
- a material in which electrons cannot move
easily from one atom to another - nonmetal
- e.g. wood, rubber, plastic – covering for wires,
wall socket protectors, screwdriver handles
CONDUCTOR
- material in which electrons can move easily
between atoms - metals
- e.g. copper and aluminum – wires
SEMICONDUCTOR
- material in which electrons can move fairly
well between atoms - nonmetals - e.g. silicon
- foundation of modern
electronics - e.g. radio, computers,
telephones,
transistors, solar cells,
digital and analog
circuits
Water: Insulator and Conductor
- pure water (no dissolved substances) = insulator
- tap water (dissolved substances) = conductor
- dry air = insulator
- moist air = conductor
Shocking Results
You feel a shock when a relatively large number of electrons flow
rapidly through your hand. People receive a small shock when they
walk in stocking feet on carpet and then touch a metal doorknob. The
excess electrons in the person’s body are discharged into the
conducting metal doorknob. If the person’s body has a positive charge,
electrons will move from the doorknob into the person’s hand.
If some of the excess
electrons are
removed by touching
the wooden door
first, then the charge
is slowly reduced
and a shock is not
felt.
* when a large number of electrons flow rapidly
through your hand you feel a shock
Grounding: Removing Static Charges
- to remove net static charge, put the object in
contact with a ground
GROUND
- has a very large number of charges
and can supply electrons to a
positively charged object and
remove electrons from a negatively
charged object so that the object
becomes neutral - the ground remains neutral
- e.g. Earth
Material Strength of Hold on Electrons
Glass
Human hair
Nylon
Wool
Fur
Silk
Cotton
Lucite (a clear plastic)
Rubber balloon
Polyester
Foam
Grocery bags (low density polyethylene)
Ebonite (a hard form of rubber)
strength of hold
weak
strong
ELECTROSCOPE
- device for detecting the presence of an
electric charge - e.g. pith ball electroscope, metal leaf
electroscope
