An Introduction to Electricity

Shocking fish tales…. electric eel Freshwater fish found in Central and South America Can produce up to 600V of electricity from muscle tissue (that’s 5 times the volts from an electrical outlet) Electricity is used for stunning prey, self-defense, and communication What is it? electric eel

Electric Charge and Static Electricity All matter is composed of very small particles called Atoms are made up of __________, _________, and ________

Electric Charge and Static Electricity All matter is composed of very small particles called Atoms are made up of protons, neutrons, and atoms electrons

Charges and their forces Two types of charges Positive and negative Atoms become charged by gaining or losing electrons Law of electric charge Like charges … repel one another Opposite charges … attract one another (electrostatic attraction) + - + +

Electric Force electric force The force between two charged objects is called the The strength of the force is determined by two factors: Size of the charge Distance between the two charges electric force

Trivia Who was the first person to realize that lightning is a huge electric discharge? Ben Franklin

Atoms are normally neutral…so how do they become charged? Friction Rubbing two objects together Conduction Electrons are transferred from one object to the next by direct contact Induction Uncharged object charges are rearranged without direct contact with charged object

Moving Charges Conductors Insulators Material in which charges can move easily Metal (copper, silver, aluminum, etc) Water (with electrolytes) Insulators Materials in which charges cannot move easily Plastics, rubber, glass, wood, etc…

Electrical energy What is an “electrolyte”? A cell or battery converts chemical energy to electrical energy Wet cell – electrolyte is contained in a solution Dry cell – electrolyte is solid or paste-like What is an “electrolyte”? An electrolyte is a liquid or gel that contains ions electrode electrolyte

Electrical Current The electricity flows because the chemical reaction causes a change in charge between the two (positive and negative) electrodes potential difference the electrical force driving the charge through the conductor expressed in volts (V) (average household batteries are one cell with 1.5V of potential difference) Current: the rate which a charge passes a given point is expressed in Amperes (A) or amps

Electrical Current Consider a waterfall The height of the fall is like the voltage The rate at which water is coming over the fall is like current Human body

Stun gun vs. electrical outlet Stun guns generate a high-voltage, low-amperage (3 milliamps) electrical charge. This means that the charge has a lot of pressure behind it, but not that much intensity. demonstation a typical household circuit can deliver 15 to 20 amps (15,000 – 20,000 milliamps) Human body

types of electrical current Two types of electrical current DC – direct current Electrical charges always travel in the one direction Electrical current produced by batteries is DC AC – alternating current Electrical charges flow in two directions (forwards and backwards along a wire) Electrical current produced by electrical generators is AC

Questions Two protons will _______ each other Repel Atoms become charged by gaining or losing… Electrons A material in which charges can move easily is a… Conductor A material in which charges can’t move easily is an… Insulator Electrical charges flow in two directions (forwards and backwards along a wire) Alternating current

Electric fields An electric field surrounds electrically charged particles The electric field exerts a force on other electrically charged objects The concept of an electric field was introduced by Michael Faraday. It is a force similar to gravity

Electric fields Electric fields can be mapped and illustrated using field lines Lines are drawn going out from positive particles and going into negative particles Lines are drawn close together to show where the field is stronger and farther apart to show where the field is weaker field lines animation 1 field lines animation 2

Electric fields

Electric fields

Electric fields

Electromagnetic Induction the production of voltage across a conductor moving through a magnetic field. It underlies the operation of generators, all electric motors, transformers, induction motors, synchronous motors, solenoids, and most other electrical machines. Discovered by Michael Faraday The magnetic field and wire must move perpendicular to each other. Produces alternating current (AC)

Electromagnetic Induction Lenz's law states, An induced current is always opposite to the motion causing it

Transistors Semiconductors are materials in which only high energy electrons can “flow.” As the temperature rises, more electrons are free to move through these materials. Semiconductors have had a monumental impact on our society. You find semiconductors at the heart of microprocessor chips as well as transistors. Anything that's computerized or uses radio waves depends on semiconductors. Today, most semiconductor chips and transistors are created with silicon. You may have heard expressions like "Silicon Valley" and the "silicon economy," and that's why -- silicon is the heart of any electronic device.

Transistors You can change the behavior of silicon and turn it into a conductor by doping it. In doping, you mix a small amount of an impurity into the silicon crystal. A diode is the simplest possible semiconductor device. It allows current to flow in one direction but not the other. A transistor is created by using three layers rather than the two layers used in a diode. A transistor can act as a switch, amplifier or AC/DC converter. transistors have almost entirely replaced vacuum tubes that were widely used in early radios, television sets, and computers. 28

Plasma a mixture of positive ions and free electrons that is electrically neutral on the whole but that can conduct electricity. created by very high temperatures when molecules break up into positively charged ions and negatively charged electrons. Much of the matter in the universe is in stars in the form of plasma Plasma is considered a fourth state of matter, as fundamental as solid, liquid, and gas.

Questions

Quick Quiz If two charges repel each other, the two charges must be A. the same B. opposite A device that can convert chemical energy to electrical energy is a A. generator B. Cell C. Electric motor A device that can convert mechanical energy to electrical energy is a A device that can convert electrical energy to mechanical energy is a generator B. Cell C. Electric motor Which type of current flows in only one direction? Which type of current flows in two directions (back and forwards) What component of a circuit can amplify an output? What is the 4th state of matter? A poor conductor of electricity is also referred to as a _______________.