ELECTRICITY: ELECTRICAL FIELDS #4

Field Basics

Scientists understood why forces acted the way they did when objects touched. The idea that confused them was forces that acted at a distance without touching. 
Think of examples such as gravitational force, electric force, and magnetic force. To help them explain what was happening, they used the idea of "field". They imagined that there was an area around the object, and anything that entered would feel a force. We say, for example, that the Moon has a gravitational field around it, and if you get close to the Moon, it will pull you down to its surface.

Electric Fields
An electric field describes the funky area near any electrically-charged object. Scientists don’t use the word "funky", but it works. It could also be called an electrostatic field. Any other charge that enters that area will feel a force, and the original object will also feel that force (Newton's Third Law). It's kind of like a spider sitting at the center of a web.

A normal field is a vector, and is represented by arrows. The Earth's (or any planet's) gravitational field would be drawn as arrows pointing toward the ground. A field vector shows the direction of the effect on an object entering the field. Gravity acts downward.

For an electric field, things are a little more complicated, since there are two kinds of charges, and some combinations attract while others repel. In order to be in agreement with each other, physicists decided that they would always use positive charges to determine the direction of the effect of a field. So, if the central charge was positive, and you put another positive charge near it, that second charge would be repelled outward. So the field vectors for a central positive charge point outward. If the central charge is negative, a positive charge placed nearby would be attracted toward the center charge, so the field vectors for a central negative charge point inward.

Since fields are directly related to the forces they exert, their strength decreases with distance, and increases with the size of the charge producing the field. When you put charges near one another, their fields interact and change shape. This results in changes in the PE of the objects, and generates forces of repulsion or attraction.

Electric fields can also be created by magnetic fields. Magnetism and electricity are always connected. 

ELECTRICITY - POWERPOINT - GO to - 

• ELECTRICAL CHARGES & CURRENTS, CHAPTER 12

ELECTRICITY: CONDUCTORS & CONDUCTIVITY #3

Conductors and Conductivity

There are many materials that allow charges to move easily. They are called conductors. Conductors have the quality of conductivity. I guess that's not a lot of help for you. The reality is that you just need to understand the difference between those two words. The conductor is the object that allows charge to flow. Conductivity is a quality related to the conductor. A material that is a good conductor gives very little resistance to the flow of charge. This flow of charge is called an electric current. A good conductor has high conductivity.

Different Types of ELECTRICAL Conductors

Electrical conductors are materials that allow electricity to flow through them easily. Most metals are good conductors.

Electrical insulators are materials that do not allow electricity to flow through them. Most plastic and ceramic materials are insulators.

In the diagram of an electrical insulator, the insulating material (plastic) surrounds the conducting material (copper wires).

(1) Metals are traditional conducting materials. You see them around the house all of the time. It's a metal wire or one of the metal prongs in an electric plug. There are a lot of free electrons in metallic conductors. Free electrons are electrons that are not being held in atoms, and so, can move easily. 

• Some of the best metallic conductors are copper (Cu), silver (Ag), and gold (Au). 

(2) There are some conductors that are not metals. Carbon is the best example.

(3) You've probably seen ionic conductors in a lab or in an experiment. When you think about ionic conductors, think about solutions and molten conductors. 

• A solution such as saltwater has a lot of free ions floating around. Those ions (charged atoms) can flow easily, and ionic solutions are very good conductors. 
• One of the reasons you need to get out of the water if there is lightning around, is that water normally contains dissolved ions, and if lightning hits the liquid (solution), it might conduct electricity long distances and electrocute you. 

(4) Semi-conductors are the conductors that make your computer possible. If it weren't for semi-conductors, most electronic doodads couldn't be made. Semiconductors have free electrons, but not as many as conductors, and they are not as easy to get moving. Semiconductors have low conductivities. 

• SEMI CONDUCTORS have both conducting and insulating properties and they are used to make electronic components. The way in which a semi-conducting material is connected to a power supply determines whether it will conduct an electrical current or prevent it from flowing.
• Examples are elements like silicon (Si) and germanium (Ge). 

Conductors and Insulators

Conductors are made of materials that electricity can flow through easily.
These materials are made up of atoms whose electrons can move away freely.

Some examples of conductors are: Copper Aluminum Platinum Gold Silver Water People and Animals Trees

Insulators are materials opposite of conductors. The atoms are not easily freed and are stable, preventing or blocking the flow of electricity.

Some examples of insulators are:

• Glass
• Porcelain
• Plastic
• Rubber

Electricity will always take the shortest path to the ground. Your body is 60% water and that makes you a good conductor of electricity. If a power line has fallen on a tree and you touch the tree you become the path or conductor to the ground and could get electrocuted.

The rubber or plastic on an electrical cord provides an insulator for the wires. By covering the wires, the electricity cannot go through the rubber and is forced to follow the path on the aluminum or copper wires.

Let Them Move

So what happens if you have separated charges and you connect them with conducting material? Providing a path for charges to move, and making that path out of materials that allow easy movement, results in a flow of charge (electrons) called a current. The electrons will flow from a location that is negative to one that is positive. This can happen quickly and then stop, as with a spark. Or, in the case of a battery connected to a conducting loop (called a circuit. ), it continues to happen until the battery runs out of energy. 

•  If the current goes in one direction all the time, it is called DC, or direct current. 
•  In your home, however, the same charges move back and forth, so this is called AC, or alternating current. 

Force of Charges

Scientists discovered that opposite charges attract, and like charges repel. So positive-positive and negative-negative would repel, while positive-negative would attract. Physicists use the term electric force to describe these attractions and repulsions. The electric forces are much stronger when negative charges are closer to positive charges. The further apart two charges are, the weaker the electric force. Also, the greater the charges, the greater the electric force will be.

ELECTRICITY: SEPARATING CHARGES #2

Separating Charges

Atoms start out with the same number of negative charges (electrons), and positive charges (protons). Under certain conditions, electrons can be removed from, or added to atoms. Removing electrons would leave the atom with more positives than negatives, and we call this a positive ion (An ion is a charged atom). Conversely, adding electrons to an atom would result in a negative ion. If you do this enough times, you can make an object positive or negative.

Friction is one of the ways to separate charge. Have you ever had a science lab where you rub fur on glass rods, or try to make static cling? When you do that rubbing, you are actually rubbing electrons off one object and onto another. When you scuff your feet on the rug, especially in the winter, you can often charge yourself. Clothes tumbling in the dryer often cling together and crackle when you separate them. Lightning is produced, in part, because of air blowing over land. You can also use batteries to separate charge.

Static Charges

Electrons can move more easily in some objects than in others. If you put a charge on things like glass, plastic, rubber, and wood, that charge stays where you put it. We say the charges are static, and we call this static electricity. 

Materials like glass and plastic are called insulators, or nonconductors. Static electricity can happen on a dry winter day when you walk across a carpet. You are actually building up loads of electrons on your skin. Charges don't "want" to stay separated, however. There is always a tendency for charges to return to their original locations, and all that is needed is a pathway for charges (electrons) to use. 

• When you touch a metal doorknob, for example, electrons can jump and give you a shock. Static charges build up on clouds until they can hold no more. At that point, lightning can occur. The study of electricity where the charges are not moving is called electrostatics.

Beware of Conductors!

If you scuff your feet on your living room rug, you pick up extra electrons and have a negative charge. Electrons move moreeasily through certain materials like metal, which scientists call conductors. When you touch a doorknob (or something else made of metal), which has a positive charge with few electrons,the extra electrons want to jump from you to t  the knob.

ELECTRICITY - MOVING ELECTRONS & CHARGES #1 ....

Moving Electrons and Charges

Electricity is related to charges, and both electrons and protons carry a charge. The amount of the charge is the same for each particle, but opposite in sign. 
Electrons carry a negative charge while protons carry positive charge. The objects around us contain billions and billions of atoms, and each atom contains many protons and electrons. 

The protons are located in the center of the atom, concentrated in a small area called the nucleus. 

The electrons are in motion outside of the nucleus in orbitals. 

The protons are basically trapped inside the nucleus and can't escape the nucleus. As a result, it is moving electrons that are primarily responsible for electricity.

There aren't a lot of places that you can see electricity. The most commonly- observed form of electricity is probably lightning. 

•  Lightning is a big spark that occurs when lots of electrons move from one place to another very quickly. 
• There are three basic forms of lightning:
•  cloud to cloud
• cloud to surface
• surface to cloud. 
• All are created when there is an unequal distribution of electrons. You can also see smaller sparks of electricity in science labs that contain Van de Graff generators, and can see even smaller arcs of electrons at home when you scuff your feet and then touch something like a metal doorknob (static electricity). 

Electricity Around You
It's easy to see the uses of electricity around you. In fact, there are charges around your computer, your house, and your city. 

• Electricity is constantly flowing through all of the wires in your town. There is also electricity in your flash light. That kind of electricity created by batteries is called direct current. The other major type is found in the outlets of your house. That household form of electricity is called alternating current.