* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Electric Current and Curcuits
Survey
Document related concepts
Electrical ballast wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Electrification wikipedia , lookup
Current source wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Power engineering wikipedia , lookup
Electric machine wikipedia , lookup
General Electric wikipedia , lookup
Buck converter wikipedia , lookup
History of electric power transmission wikipedia , lookup
Voltage optimisation wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Rectiverter wikipedia , lookup
Stray voltage wikipedia , lookup
Surge protector wikipedia , lookup
Mains electricity wikipedia , lookup
Transcript
Electric Current and Circuits 17-2 and 17-4 Q: What part of the newspaper do electricians read first? A: Current Events! Electrical Energy • Electrical energy is the energy found in electric charges (carried by electrons) – As you already know, charged objects exert a push or pull on other charged objects • Electrical charges mostly flow through wires • This flow of charges is called an electric current Electric Current • An electric current is the rate that the charges pass a given point – How many pass in a certain amount of time – The higher the current, the higher the number charges that pass that point each second • Measured in amperes (usually called amps) • The symbol for ampere is A and the symbol for current is I when writing equations Its electric (boogy woogy woogy) • When a light switch is turned on, the wires connect, creating an electric field that moves at the speed of light – Remember, an electric field is the place around a charged object where an electric force can act on another object • The electric field causes any free electron in the wire to move • The energy of each electron is transferred instantly to the next electron AC/DC (not the band) • Two kinds of current – Direct current (DC) • Charges always flow in the same direction • Usually found in electric objects that require a lower current • Ex: batteries, cameras, stereos, etc… – Alternating current (AC) • Charges reverse from flowing in one direction, to flowing in the other at certain intervals • Usually found in electric objects that require a higher current • Ex: outlets in your home Voltage • The potential difference between two points in a curcuit – Expressed in volts (V) – How much work is needed to move a charge between two points • It is the amount of energy released as a charge moves – The higher the voltage, the more work is needed to move the charges, and the more energy is released by each charge • Voltage is like the hill you ride down on your bike because the higher the hill, the faster the bike – the higher the voltage, the more energy is released Voltage and Current • As long as there is voltage between two points, charges will flow in the wire • The size of the current depends on the voltage – The greater the voltage, the greater the current • A greater current means that more charges move in the wire each second Voltage and you • Most US outlets supply a voltage of 120V, so your appliances and electronics run on 120V – An electric eel can create a voltage of more than 600V – That’s enough to power 5 appliance/electronics at the same time!!!! Resistance – “Electric Friction” • The opposition to the flow of electric charge – Expressed in ohms • The symbol in equations is R – Stops charges from moving – The higher the resistance, the lower the current • So if voltage doesn’t change, as resistance goes up, current goes down – Depends on the object’s material, thickness, length, and temperature Resistance… • And material – Good conductors have low resistance • Used to make wires – Poor conductors (insulators) have high resistance • The high resistance of the filament in a light bulb causes the light bulb to heat up and give off light • And thickness – Thicker wire has lower resistance than a thin pipe because there is more room for the charges to flow Resistance… • And length – Shorter wire has lower resistance than a long pipe because less work is needed to make the charges travel • And temperature – Resistance of metals increases as temperature increases • Higher temperatures mean atoms move faster and they get in the way of the flowing charges – Materials that are cooled to very low temperatures so that the resistance drops to 0 ohms are called superconductors • Very little energy is wasted in them because there is no resistance Generating Electrical Energy • You already know that energy cannot be created or destroyed – It can only be changed into other kinds of energy • Generators convert mechanical energy (kinetic and potential energy) into electrical energy (light and heat) • Cells change chemical or radiant (sun’s) energy into electrical energy – Batteries are made up of one or two cells • End of section 14-2 Electrical Circuits • Roller coasters and electric circuits are similar in that they both start and end at the same place – they form a loop • Electric circuits – complete, closed paths through which electric charges flow Parts of a circuit • Energy source – IE: battery • Wires – Usually copper surrounded by some type of insulation • Load – Ie: light bulbs, radios – Connected to the energy source by wires – Change electrical energy in other forms of energy (thermal, light, mechanical, etc…) One more part • Circuits may also contain a switch – Used to open or close the circuit – When the switch is in the off position, the circuit is open, so charges can not flow through it – When the switch is in the on position, the circuit is closed, so charges can flow Series circuits • Circuit in which all parts are connected in a single loop – Ie: christmas lights – Only one path for charges to flow • If there is any break in the circuit, all charges will stop flowing, none of the loads will work – All of the loads (lightbulbs) share the same current so they shine with the same brightness – If you add more lightbulbs, more resistance is added, so the light will dim Parallel circuits • A circuit in which loads are connected side by side – Ie: your house • If your home were wired in series circuits, turning on the light in your room, would turn on everything in your house – Charges in parallel circuits have more than one path that they can travel through – Loads all use the same voltage