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 througha 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 q1q2

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 -12C)

(9.0 x 10 -4 m2)

= + 1.8 x 10 -8 N

MAGNETIC FIELDS

Magnetic field lines

1. Leaves north pole & enters south pole

2. Lines closer together = stronger field

NOTICE

3. Strongest at the poles

4. Field lines start at the NORTH pole and travel towards the SOUTH pole

An area where the force exists; area where force is felt

We used g= force/mass to measure the gravitational field and E= force/charge to measure the electrostatic field.

Finding the strength of magnetic fieldEqn: B= F/p

Where: F = is the force in newtonsp = is the pole strength in

ampere- metersB = is the magnetic induction in

newtons/ampere-meter

ExampleAt 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 fieldEqn: B= Φ

A

Where: B and A are perpendicular Φ = flux in webersA = 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

Qv