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 electric eel

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

Potential Energy GPE GPE Example

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

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

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.

Plasma What are some examples of plasmas? Amazing Northern Lights Time Lapse Aurora Australis 1 Aurora Australis 2

Transistors Semiconductors 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 What type of element is silicon? Semimetal (metalloid) Would you expect silicon to be a conductor of electricity or an insulator? 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. 22

Transistors 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. For example, a device that uses batteries often contains a diode that protects the device if you insert the batteries backward. The diode simply blocks any current from leaving the battery if it is reversed -- this protects the sensitive electronics in the device. 23

Transistors How Transistors Work 25

Questions