Current

Vocabulary Current Electricity: flow of charged  particles in a complete circuit Current (I): Amount of charge passing a point in a conductor per second Ampere (A): unit for measuring current defined as: one coulomb/second Ammeter: device used to measure current

Electric Circuit Any complete pathway that allows electrons to leave a source and eventually return to that source An electric circuit consists of three things: A source of energy At least one battery Electrons flow through devices (loads) that convert electricity into other forms of energy Loads are things like: light bulb, motor, heater, etc. A closed path to carry energy from the source to the load (the wires)

Batteries Chemical E in the battery gives the e- on the negative terminal of the battery potential energy. e- are attracted to the positive terminal (+ and – are kept separated in a battery) The wire is the pathway they e- can travel through e- leave the negative terminal and are pushed by the E of the battery (voltage) Electrical E is converted into light energy in the light bulb (load) e- complete the circuit by travelling the rest of the way back to the positive terminal of the battery

Upon returning to the source, all of the Electric potential energy in the charge must be converted to other forms of energy

Conventional Current Ben Franklin originally named charges positive(+) and negative(-) when he was studying static electricity. Franklin assumed that an electric “fluid” flowed from a positive object into a negative object, and that became the “convention”. This was before electrons were discovered! For this reason, conventional current describes Franklin’s original ideas of positive flow...which is backwards!

Conventional Current The actual flow of electricity is from negative to positive (the flow of electrons). So, when we use the term current, we are describing electron flow, which is from negative to positive. When we use the term conventional current, we are describing reverse electron flow, which is from positive to negative.

Conventional Current It is confusing, but once a convention is made and other principles are based upon it, it is difficult to correct it! We know that electrons move through the wire toward the positive terminal, but this diagram shows positive flowing to negative! Called “Conventional Current” An unfortunate and confusing convention!

Basic Circuit Components and Diagrams Four basic components: Source: source of energy Conductor: wire where current flows Electric Load: turns electricity into other forms Switch: turns circuit on or off

Circuit Diagrams All circuit diagrams should be drawn using a ruler. All turns in the circuit should be drawn at 90° angles. Not all circuit diagrams will be identical the size & spacing of the components is not important, but the components should be in the same order as the initial illustration. The battery in a circuit may be symbolized as either a battery or a cell. Modern convention is to use the cell symbol to represent both cells and batteries

Electrons are so Pushy! As each e- moves through a conductor, it pushes on the one ahead of it  all the e- move together as a group The starting and stopping of e- flow is virtually instant Imagine a tube filled end-to-end with marbles: The tube is full of marbles just as a conductor is full of free e- ready to be moved by an outside influence If a single marble is suddenly inserted into this full tube on the left-hand side, another marble will immediately try to exit the tube on the right Even though each marble only traveled a short distance, the transfer of motion through a tube is instantaneous from the left end to the right end, no matter how long the tube is With electricity, the overall effect from one end of a conductor to the other happens at the speed of light (a speedy 299 792 458 m/s!)