Electrity

Question 1

Electricity

Answer 1

• form of energy
• results from interaction
  of charged particles
  (e.g. –ve electrons or
  +ve protons)

Question 2

STATIC CHARGE (STATIC ELECTICITY)

Answer 2

• 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.

Question 3

CHARGING BY FRICTION

Answer 3

• 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

Question 4

Causes of Electric Charges

Answer 4

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

Question 5

Causes of Electric Charge

Answer 5

• movement of
  electrons!
• why electrons?
  – because they have a
  small mass and are
  further from the
  nucleus.

Question 6

Electrostatic series

Answer 6

• 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.

Question 7

INSULATOR

Answer 7

• 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

Question 8

CONDUCTOR

Answer 8

• material in which electrons can move easily
  between atoms
• metals
• e.g. copper and aluminum – wires

Question 9

SEMICONDUCTOR

Answer 9

• 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

Question 10

Water: Insulator and Conductor

Answer 10

• pure water (no dissolved substances) = insulator
• tap water (dissolved substances) = conductor
• dry air = insulator
• moist air = conductor

Question 11

Shocking Results

Answer 11

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

Question 12

Grounding: Removing Static Charges

Answer 12

• to remove net static charge, put the object in
  contact with a ground

Question 13

GROUND

Answer 13

• 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

Question 14

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)

Answer 14

strength of hold

weak

strong

Question 15

ELECTROSCOPE

Answer 15

• device for detecting the presence of an
  electric charge
• e.g. pith ball electroscope, metal leaf
  electroscope