Electricity and Magnetism

Atom Review Electrons have a negative charge (-) Protons have a positive charge (+)

Like charges repel each other Unlike charges attract each other

electric field: the field around charged particles that exert force on other charged particles

A charged particle in the electric field of another particle will either be pushed or pulled, depending on the charge.

Static Charge Protons are bound tightly in the nucleus of an atom, but electrons can sometimes leave the atom

Insulator: a material through which charges of an electrical current are not able to move Ex. wood, rubber, glass

Conductor: A material through which electrons can move freely Ex. copper, gold, aluminum

If an object loses electrons, then it has an overall positive charge. If an object gains electrons, then it has an overall negative charge.

static electricity: the buildup of charges on an object Van de Graaf generator: produces static electricity

Charges can be transferred to one another in three ways: 1. friction 2. conduction 3. induction

Friction: transfer of electrons by rubbing

Conduction: transfer of electrons from one object to another by direct contact

Induction: movement of electrons to one part of an object caused by the electric field of another object

Law of Conservation of Charge: Charges cannot be created or destroyed. Electrons can only be transferred from one object to another.

Examples of static electricity: Static cling in the dryer Plastic wrap

When a negatively charged object and a positively charged object come together, the electrons move until the charges balance out

static discharge: the loss of static electricity as electrons move off an object - this can also be called GROUNDING

Examples of static discharge: shock from walking across a carpet and touching something made of metal lightning

- It is always better to err on the side of caution – if you see lightning and you are outside – GET INSIDE - Always turn off electricity at the circuit breaker before attempting home repairs Electrical Safety

- the 3 rd prong found in most electrical outlets is for the “ground” wire; it provides a path for electricity to reach the ground in case of a surge (it helps to protect both the equipment and helps to prevent electrical fires within the walls of your home) - Under NO circumstances should you EVER remove the 3 rd prong of a cord to fit a plug into a 2 prong outlet

Electrical Circuits

electrical potential: the potential energy per unit of electrical charge

voltage: the difference in the amount of electrical potential between 2 objects

- measured in volts (V) voltmeter: device used to measure voltage

Electrons will flow as long there is a difference in the electrical potential Voltage causes current to flow through an electrical circuit

electrical circuit: a complete path through which electrical charges can flow

voltage source: creates a potential energy difference in an electrical circuit ex. batteries and generators

current (I): the flow of electric charges through a material measured in Amperes (A) ammeter: device used to measure current

resistance: the opposition to the movement of electric charges through a material measured in Ohms (  )

- depends on the thickness and length of a wire, as well as how well the material conducts electricity

resistor: a device in electrical circuits that uses electrical energy as it interferes with the flow of electric charge

The greater the resistance, the less current there is for a given voltage

If an electrical current can travel through one of two paths, it will choose the “path of least resistance”

Inside an XBox 360

Ohm’s Law Resistance = Voltage Current

OR V IR

Types of Circuits: Series & Parallel

Series Circuit: a circuit where there is only one path for the current to take - all parts of the circuit are connected one after another

A series circuit

ex. Xmas tree lights - if one bulb burns out, the whole strand goes out because there is no other path for the current to take

When more resistors, (ex. light bulbs) are added to the circuit, the light becomes dimmer.

Remember! If resistance increases, then current decreases. Therefore, the bulbs will burn less brightly.

Parallel Circuit: a circuit that has several paths for the current to take - different parts of the circuit are on separate branches

A parallel circuit

If one bulb burns out, the rest of the lights stay on because the current can move through the other branches.

As additional resistors are added, the brightness of the light does not change

Electromagnetism

magnetism: the attraction of a magnet for another object magnetic pole: the area of a magnet where the magnetic effect is the strongest

Poles that are alike repel each other, poles that are unlike attract each other.

magnetic field: region of magnetic force around a magnet

magnetic domain: a cluster of billions of atoms that all have magnetic fields that are lined up in the same way

In a magnetized material, all or most of the domains are arranged in the same direction That means that all the domains are aligned!

Magnets can lose their magnetic properties by being dropped, struck hard or heated. (the domains are knocked out of alignment)

When a magnet is broken in half, it does NOT lose its magnetism, it simply becomes 2 magnets!

An electric current produces a magnetic field.

solenoid: a current carrying coil of wire with many loops - creates a magnetic field that can be turned on and off

electromagnet: a strong magnet that can be turned on and off

Examples of electromagnets: - solenoid - junkyard crane - tape recorder

Generating Electricity An electric current will be produced in a conductor when the conductor moves across the lines of a magnetic field.

electromagnetic induction: the process of generating an electric current from the motion of a conductor through a magnetic field

The flow of an induced current may be constant or may change direction

alternating current (AC): a current consisting of charges that move back and forth in a circuit ex. the circuits in your home

direct current (DC): current consisting of charges that flow in one direction ex. battery