Page 318 - (DK) The Ultimate Visual Dictionary 2nd Ed.

PHYSICS AND CHEMISTR Y
Electricity VAN DE GRAAFF (ELECTROSTATIC) GENERATOR

Positive charges Metal
dome
at many thousands
and magnetism of volts

ELECTRICAL EFFECTS result from an imbalance of electric charge. Rotation
There are two types of electric charge, named positive (carried by of belt
protons) and negative (carried by electrons). If charges are opposite
(unlike), they attract one another, while like charges repel. Forces
of attraction and repulsion (electrostatic forces) exist between Positively charged Pulley
belt strips negative wheel
any two charged particles. Matter is normally uncharged, but if charges (electrons)
electrons are gained, an object will gain an from dome via metal
overall negative charge; if they are removed, comb, giving dome a
positive charge
it becomes positive. Objects with an overall
negative or positive charge are said to have Moving rubber Insulating
belt gains a column
an imbalance of charge, and exert the same positive charge prevents
forces as individual negative and positive charges
charges. On this larger scale, the forces will Positive metal leaking
comb strips away
always act to regain the balance of charge.
negative charges Negatively
This causes static electricity. Lightning, for (electrons) from belt charged
example, is produced by clouds discharging a metal plate
huge excess of negative electrons. If charges Connection
LIGHTNING
are “free”—in a wire or material that allows to positive Pulley
electrons to pass through it—the forces cause a flow of charge electrical wheel
supply
called an electric current. Some substances exhibit the strange
Rotation
phenomenon of magnetism—which also produces attractive and Connection of belt
repulsive forces. Magnetic substances consist of small regions to negative
electrical supply
called domains. Normally unmagnetized, they can be magnetized
by being placed in a magnetic field. Magnetism and electricity
are inextricably linked, a fact put to use in motors and generators.
CURRENT
ELECTRICITY Junction Metal wire
(conductor)
Crocodile clip Direction of Four 1.5 volt cells VOLTAGE coated with
connector current, opposite (total of 6 volts) The higher the voltage, plastic (insulator)
to electron flow the greater the energy of
Bulb receives by convention electrical charges. One
3 volts volt is one joule (unit of Bulb holder
Electrons energy) per coulomb
Bulb holder flow from (unit of charge). Bulb receives
negative 6 volts
terminal Negative terminal
Metal wire to positive Bulb has high
(conductor) terminal Positive terminal resistance
coated with
plastic (insulator) CURRENT RESISTANCE
The greater the number of For a given voltage,
Switch electrons moving around the the flow of current
Bulb receives completes circuit, the higher the current. depends upon the
3 volts or breaks Current is measured in amps (A). resistance of a circuit.
circuit One amp equals one coulomb Resistance is the
Bulb holder (unit of charge) per second. degree to which a
substance resists
electrical current.
It is measured in
ohms (Ω).
SERIES ELECTRICAL CIRCUIT SIMPLE ELECTRICAL CIRCUIT

316