PSC 4011: Static Electricity & Magnetism Electricity
describes all of the phenomena caused by positive charges (protons)
and negative charges (electrons) If a body (atom/molecule or
object) has MORE PROTONS than electrons, it will be positively
charged. If a body has MORE ELECTRONS than protons, it will be
negatively charged.
Slide 3
PSC 4011: Static Electricity & Magnetism Electrically
charged objects, which have gained or lost ELECTRONS, tend to exert
a force on other objects nearby. Like charges (+ + or - - ) will
tend to REPEL each other. Opposite charges (+ - ) will tend to
ATTRACT each other. Charges, are conserved.
Slide 4
PSC 4011: Static Electricity & Magnetism When an object has
the exact same number of protons and electrons it is called
NEUTRAL. Charging an object consists in creating an imbalance in
the electrical charge of that object. Materials can be divided in
three groups, according to their reaction to the process of
charging: Conductors Semiconductors Insulators
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PSC 4011: Static Electricity & Magnetism Every object fits
somewhere along this conducting continuum Where do you think the
human body would fit in the above diagram?
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PSC 4011: Static Electricity & Magnetism Conductors :
permit the free flow of electrical charges. When charged, its
electrons move in one general direction, pushing one another and
making the charge move along the circuit. Metals and electrolytic
solutions are conductors (ions).
Slide 7
PSC 4011: Static Electricity & Magnetism Insulators: impede
the free flow of electrical charges. When charged, its electrons
are strongly held by the atomic nuclei, so charges do not move.
Wood, glass, plastic, ceramics, paper, rubber, silk and air are
also insulators.
Slide 8
PSC 4011: Static Electricity & Magnetism Static electricity
(electrostatics) describes all the phenomena related to electrical
charges at rest. Charges are at rest when they are INSULATED.
Static charge is often detected by a device known as an
electroscope. There are three methods for charging objects.
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PSC 4011: Static Electricity & Magnetism DateEvent 6 th
century BC_Thales discovers the electrical attraction of rubbed
amber 1600_Gilbert discovers that many materials can be electrified
_Bodies are divided into 2 categories: conductors & insulators
_The human body is discovered to be a conductor 1746_Musschenbroek
makes the first Leyden jar 1760_Franklin invents the lightning rod
1785_Coulomb establishes his law (Coulombs law) ~ 1790_Galvani
believes to have demonstrated that animals body is an organic
Leyden jar 1800_Volta invents the first cell (birth of
electrodynamics)
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PSC 4011: Static Electricity & Magnetism Charging by
friction: Two neutral bodies rubbed against each other. Some
electrons are pulled from one of them. Resulting: two opposite
charged bodies (attraction!)
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PSC 4011: Static Electricity & Magnetism Charging by
friction:
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PSC 4011: Static Electricity & Magnetism Charging by
conduction: Two solid bodies in contact with each other. The charge
is transferred from the charged object to the second object.
Resulting: two equally charged bodies, each with less charge than
initially
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PSC 4011: Static Electricity & Magnetism
Slide 14
Charging by induction:
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PSC 4011: Static Electricity & Magnetism Charging by
induction:
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PSC 4011: Static Electricity & Magnetism Charging by
induction:
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PSC 4011: Static Electricity & Magnetism Precautions
(Static Electricity): Objects must be grounded in order to
eliminate static charge built on them
Slide 18
PSC 4011: Static Electricity & Magnetism Applications
(Static Electricity): Objects are previously electrified, so their
charge is kept, and attraction is guaranteed when in use
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PSC 4011: Static Electricity & Magnetism
Slide 20
Example 1: For two positively charged particles, each with a
charge of 5x10 -8 C and placed 1cm apart. Calculate the electrical
force between the two particles:
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PSC 4011: Static Electricity & Magnetism F e = k(q 1 )(q 2
)/r 2 F e = (9 x 10 9 Nm 2 /C 2 )(5 x 10 -8 C)(5 x 10 -8 C)/(0.01m)
2 F e = (9 x 5 x 5) x 10 [9+(-8)+(-8)] / (0.0001) (Nm 2 /C 2
)(C)(C) / (m 2 ) F e = (225) x 10 -7 / 1 x 10 -4 N F e = [(225)/1]
x 10 [(-7)-(-4)] N F e = 225x 10 -3 N F e = 0.225 N
Slide 22
PSC 4011: Static Electricity & Magnetism Magnetism:
Physical phenomenon produced by the motion of charge, resulting in
attractive and repulsive forces between objects
Slide 23
PSC 4011: Static Electricity & Magnetism DateEvent
BC_Scientists observed an attraction between magnetite and iron 11
th century_Chinese and Arab sailors used compasses ~1270_Compass
appears in Western Europe _Maricourt distinguishes North and South
poles 1600_Gilbert fails to relate electricity and magnetism
Slide 24
PSC 4011: Static Electricity & Magnetism Magnets: Objects
upon which magnetism is observed. Magnets ALWAYS have two poles:
North and South (if you break a magnet, you create two smaller
magnets, each with its north and south poles)
Slide 25
PSC 4011: Static Electricity & Magnetism Magnetic field:
Magnetic influence of a magnet on its surroundings. Magnetic field
lines: Representation of the magnetic field of a magnet. Lines exit
North pole Lines enter South pole
PSC 4011: Static Electricity & Magnetism Earth is a
gigantic magnet
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PSC 4011: Static Electricity & Magnetism Electric
forceMagnetic force _It acts on two types of charges (positive and
negative) _Magnets have two types of poles (North and South) _Like
charges: repulsion _Different charges: attraction _Like poles:
repulsion _Different poles: attraction _Objects CAN have ONE type
of charge (positively or negatively charged) _Magnets CANNOT have
ONE type of pole (North or South) _It is inversely proportional to
the square of the distance between the charges _It is inversely
proportional to the square of the distance between the objects