10.2 Flashcards
ELECTROSCOPE
- device for detecting the presence of an
electric charge - e.g. pith ball electroscope, metal leaf
electroscope
Charging by Contact and Induction
The presence of electric charges can be detected using a simple device
called an electroscope.
Most electroscopes indicate that a
charge is present by having either a
component that moves to one side or the
other or components that move apart.
In the example in the large photo on the
left, the two metal leaves move apart
when the charged object is touched to
the electroscope. In the small image, a
small ball (pith ball) is moving away
from a charged object.
CHARGING BY CONTACT
- generating a charge on a neutral object by
touching it with a charged object - charge can be positive or negative, or none
(neutral) - electrons move on or off the object
- protons do NOT move
- an object that becomes charged by contact
always gets the same type of charge that is on
the object that charges it
Charging by Contact
The image below illustrates how charges are transferred through contact. (Pages 412-3)
LAWS OF ELECTRIC CHARGES
- describe how two objects interact electrically
when one or both are charged
The Amount and Type of Charge
- amount of net charge depends on difference
between the number of protons (p+
) and
electrons (e-
)it contains.
- to determine whether an object is charged you
must observe repulsion between it and another
object (use the laws of electric charges)
– e.g. if a positive object is attracted to an object of
unknown charge then the unknown charge must be
negative
– if object is attracted to both + and – charges, you
know it is neutral
ELECTRIC FIELD
- space around a charged object
- produce an electric force on any other objects
in the field - electric forces between two objects are
transmitted through an electric field at the
speed of light - includes repulsions and attraction
- increase strength of electric field by:
– decreasing distance between objects
– increasing net charge
A A positively charged object repels positive objects in its field.
B A negatively charged object attracts positive objects in its field.
CHARGING BY INDUCTION
- = induced charge separation
- when a charged substance is brought close
(but does not touch) a neutral object, its
electric field causes (induces) electrons to
move in the neutral object
Charging By induction
➢ When a charged object is close to a neutral object, its
electric field produces a force on the neutral object.
➢ The charged object causes the electrons in the neutral
object to move.
➢ This movement of charges can result in portions of the
neutral object developing a negative charge, and other
areas developing a positive charge.
Summary (3 methods)
3 methods of charging:
1. Charging by FRICTION
➢ Rubbing two objects together.
➢ Objects have opposite charges depending on their placement in
the electrostatic series; both objects will be charged.
➢ Strong hold on electrons gain e-(negatively charged) and weak
hold on electrons lose e- (positively charged).
- Charging by CONTACT
➢ Touching two objects, one that is charged, together.
➢ Neutral object gains the same charge as the charged object.
➢ Both objects will be charged.
3. Charging by INDUCTION
➢ Bringing two objects, one that is charged, close to each other
without touching.
➢ Charged object remains charged (+ve or –ve) while the other
object remains neutral.
➢ Electrons move in the neutral object depending on the charge on
the charged object.
10.3 charges at work
➢ A lightning bolt is an
example of a
gigantic electrical
discharge.
➢ Moderate
thunderstorms
generate as much
energy as a small
nuclear generating
plant.
Lightning
➢ Storm clouds contain
a complicated mix of
raindrops, ice
particles and air.
➢ As these materials
swirl around within
the cloud, charges
are transferred and
ions (charged atoms
or groups of atoms)
are formed.
(Page 418)
Lightning 3
➢ Lightning bolts
represent the
**instantaneous
discharge **of the
charges that have
built up within a
cloud.
➢ The lightning bolt
generally hits the
highest object in an
area.
Lightning Rods and Safety
Lightning rods are
metal spheres that are
connected to the
ground with a thick
insulated metal cable.
Lightning rods reduce
the likelihood of a
lightning strike and
safely conduct the
charge to the ground if
a strike does occur.
Lightning Rods and Safety
In Canada, most lightning
storms occur in June,
July, and August.
The Van de Graaff Generator
Van de Graaff
generators are devices
that accumulate very
large charges.
The Van de Graaff Generator
A rubber belt inside the
generator is charged by
friction as it moves around
two rollers. The charge is
transferred to a metal
comb attached to the
sphere, where it builds up.
The charge is
then transferred
to anyone who
touches the
sphere, with hair-
raising results.
