Download electricity and magnetism

ELECTRICITY AND
MAGNETISM
ELECTRICITY
 Is a basic feature of matter that makes up
everything in the universe. When most people
hear electricity, they think of lights,
television, microwave ovens, computers, air
conditioners, and other electrically powered
devices. Electricity makes these and many
other useful things possible. But electricity is
much more important than that.
 Electricity and magnetism together make up
a force called electromagnetism, one of the
fundamental force of the universe. Electrical
force is responsible or holding together the
atoms and molecules from which matter is
composed. In this way, electricity determines
the structure of every object that exists.
 Electricity is also associated with many
biological processes. In the human body,
electrical signals travel along the nerves,
carrying information to and from the brain.
Electrical signals tell the brain what the eyes
see, what the ears hear and what the fingers
feel. Electrical signals from the brain tell
muscles to move. Electrical signals even tell
the heart when to beat.
 Electricity and electron comes from the greek
word “elektron” (the former greek work for
amber).
 Lodestone or magnetite- black rock (also
attract things).
Kinds of Electricity
•Static Electricity
Static Electricity
is caused when particles
of opposite charge get
separated. The two
kinds of particles are
attracted to each other.
When the attraction
becomes strong enough,
the particles quickly
stream back together.
Kinds of Electricity
• Electric Current
An electric current is the flow of electrons through a
material. Materials that carry a current are called
conductors. Metals are the conductors, so electrical wires
are made of metal. Most wires that are used to carry electric
current are made of copper.
Materials that do not conduct electricity are called
insulators. Rubber and plastic are both good insulators.
Most electrical wires are rapped in rubber. The rubber
prevents shocks.
An electric current needs a complete path in which to
move. This path is called a circuit. If a circuit is broken, the
current also stops flowing.
Kinds Of Electric Current
 Direct Current / DC
- the electrons always move in the same
direction
 Alternating Current / AC (wall
outlets)
- the electrons in the circuit
move rapidly back and forth
Magnetism
 Magnetism comes from the
electron in atoms.
Electrons spin like little
tops. And every electron
has an invisible area of
magnetism around it. This
area is called the magnetic
field. In some metals, the
spinning electrons turn
each atom into a tiny
magnet. Those atoms can
be made into line up in the
same direction. Then the
entire piece of the metal
becomes magnetic. Most
magnets are made of iron.
STATIC ELECTRICITY
Static Electricity
 Electrons are displaced
WITHOUT moving through
a conductor
e- displaced & builds charge (not moving through a
conductor)
Eventually electrons “jump” to a positively charged
object
Examples
• Plastic sheet & hair
• Walking on carpet &
• Touching a metal doorknob
•
Moving magnet can generate electricity.
•
Electric currents cause magnetism.
Law of Charges
 All like charges repel ( push away from ) each
other
 All unlike charges attract ( pull towards ) each
other
 Static electricity is an imbalance of electric
charges within or on the surface of a material.
The charge remains until it is able to move
away by means of an electric current or
electrical discharge. Static electricity is named
in contrast with current electricity, which
flows through wires or other conductors and
transmits energy
Coulomb’s Law
Fe = k q 1 q 2
r2
Where:
Fe = is the electric force in Newtons (N)
k = is a constant equal to 8.99 x 109 Nm2/C2
q1 and q2 = are charges in Coulombs ( C )
r = is the center-to-center distance
between the charges in meters
Example
 A positive charge of 6.0 x 10 -6C is 0.030m from a second
positive charge of 3.0 x 10 -6C. Calculate the force
between the charges.
Fe = k q1 q2
r2
= (8.99 x 109 N m2/C2 ) (6.0 x 10 -6C) (3.0 x 10 -6C)
( 0.030m )2
= (8.99 x 109 N m2/C2 ) (18.0 x 10
(9.0 x 10
= + 1.8 x 10
-8
N
-4
-12C)
m2)
MAGNETIC FIELDS
An area where the force exists; area where force is felt
Magnetic field lines
1. Leaves north pole & enters
south pole
2. Lines closer together =
stronger field
NOTICE
1. Strongest at the poles
2. Field lines start at the NORTH
pole and travel towards the
SOUTH pole
 We used g= force/mass to measure the gravitational
field and E= force/charge to measure the
electrostatic field.
 Finding the strength of magnetic field
Eqn:
 Where:
B= F/p
F = is the force in newtons
p = is the pole strength in amperemeters
B = is the magnetic induction in
newtons/ampere-meter
Example
At a certain point in a magnetic field, a 2-ampere-meter test pole has a
maximum force of 10 newtons south exerted upon it. What is the
strength and the direction of the magnetic field at this point?
B= F/p
= 10 N south/ 2 ampere-meters
= 5 N/ ampere-meter, south
Flux lines (called webers)
 Finding the magnitude of magnetic field
Eqn:
B= Φ
A
 Where: B and A are perpendicular
Φ = flux in webers
A = area in meters2
B = is the magnetic induction in
webers/meters2 and is the
magnitude of the field-meter
Example
At a certain point in a magnetic field, there are
100 webers per 5 meters2 of area. What is the
magnitude of the field?
B= Φ
A
= 100 Wb/ 5m2
= 20 Wb/m2
= 20 N/ampere-meter
Electromagnetism
If you take a soft iron nail, wrap a several turns of
insulated wire on it, connect it on a battery, you
will find that the iron nail exhibits the properties
of a permanent magnet as long as charge flows
in the wire. What most people do not realize is
that if the nail is withdrawn from the coil, the
coil still behaves in every way like permanent
magnet, but with weaker magnetic properties.
The Magnetic Force on a
Moving Charge
 Whenever a moving electric charge enters an
external magnetic field, the magnetic field
associated with the charge interacts with the
external field. This results in a magnetic force
that tends to push the charge in sideways.
 Using a Right Hand Screw Rule, point your
thumb in the direction of the velocity of the
moving charge. Since velocity and magnetic field
are perpendicular with each other, the thumb
points to the direction of the charge, and the
direction of the magnetic field is through your
fingers.
 F= Bqv
 Where: F is the magnitude of the force in newtons
B is the magnetic induction in webers/meters2
Q
v