ELECTRICITY Now that s shocking!
Electricity & Circuits Quantity Chart Quantity Variable in Formula Unit Unit s Symbol Charge q Coulombs C Potential Difference V Volts V Voltage V Volts V Current I Amps or Amperes A Resistance R Ohms Ω Power P Watts W
What is electricity? Electricity is a physics phenomenon associated with stationary or moving electrons Say what?!? Electricity is a measurement of moving or stationary electrons on or through a substance
Electricity What is Charge? Charge is a measurement of electrons or charged particles that are grouped together Charge is measured in Coulombs (C) An electron is equal to 1.60x10-19 Coulombs of charge Or 0.000 000 000 000 000 000 160 C That s super small!
Electricity What is Voltage? Voltage is a difference in electrical energy between two points inside a circuit Symbol: V Unit: Volts (V) Also known as Potential Difference Think of a battery It has a positive and negative end The difference in electrical potential energies between these two points gives us the battery s voltage rating
Electricity What is a circuit? A circuit is a path through which electrons are able to move Typically, a circuit s beginning and ending are the voltage source A.K.A the battery
Voltage Voltage is measured in volts (V) 1 V = 1 W/A This unit is named for Alessandro Volta, an Italian scientist who was able to re-animate frog legs using a crude battery
Alessandro Volta The Frog Experiments Luigi Galvani (1737-1798), a professor at the University of Bologna, showed how frog legs could be induced to twitch when connected to an electric machine, laid out on a metal table during a thunderstorm or hung from a line by brass hooks outdoors. Therefore, electricity is a substance stored and/or produced in the muscles Volta argued that the body produces this electricity to stimulate muscles into motion instead and that Galvani s experiment s results came from outside sources
Alessandro Volta The Frog Experiments Volta recreated Galvani s electrical interaction by placing two different metals (silver and zinc) on top of one another They were soaked in a brine solution first To measure how much currents was produced, Volta used his tongue as his measuring device
Electrical Systems What is Current? Current is the speed at which charge is moving past a point in a circuit. Charge per unit of time Symbol: I Current is measured in Amperes or Amps (A) 1 Amp = 1 Coulomb per second 1 A = 1 C/s 1 A = 6.20x10 19 e - /s That s electrons per second The French mathematician Andre-Marie Ampere is credited with this discovery due to all his work connecting electricity and magnetism
Resistance Resistance the measure of a material s ability to block the flow of electricity What is the flow of electricity called? Current Materials with high resistances do not allow much current to flow
Resistance George Ohm A teacher who was a pioneer in the new science of electricity (1827) He was mocked and ridiculed for his ideas It was roughly ten years before his ideas where finally accepted and he was given a professorship in Munich The unit for resistance is the Ohm (Ω) 1 Ω = 1 V/A
Resistance How is resistance measured? Resistance is measured by the formula: Where V is the voltage of the circuit Where I is the current of the circuit Where R is the resistance of the circuit This is known as Ohm s Law
Example #1 What is the resistance of a circuit when the power source supplies 25 V of voltages and has a current of 5 A?
CURRENT EVENTS Tesla vs. Edison
Current Current is the rate of moving electric charge (q) over a given period of time (t) how fast electrons are moving through a circuit e -
Current Direct Current (DC): The electrons only flow in one direction through the circuit First explored by Thomas Edison Common sources: Batteries Alternating Current (AC): The electrons flow backwards and forwards through the circuit First explored by Nikola Tesla Common Sources: Generators
Current The Great Debate: vs.
Current The Great Debate of Electricity: Edison and Tesla were both very famous scientists. Tesla was more of a mad scientist by the standards or the day (or even today). Edison (famous for his new electric light bulb) thought that Alternating Current was weak and was only good for one thing: electrocutions. To show that Tesla s idea of electric current has only one use, Edison electrocuted an elephant in front of a large crowd Today we use a mix of AC and DC. Most household items run on DC, but we transfer the electricity by means of AC.
Common Electrical Facts Alternating Current (AC) is amazing at traveling long distances Transformers step down the voltage to useable amounts for our homes Direct Current (DC) is great at powering most electrical devices Light bulbs are rated in units of watts (W) The electric voltage running through the wires in American households is 120 V Electric companies base their rates on kilowatt-hours Why? A kilowatt is a unit of power, where hours is a unit of time. A kilowatthour is therefore a unit of power x time, which is also work or energy! So what does the Power Company really sell?
Electric Power
Example 1 A 1050 W electric toaster operates on a household circuit of 120 V. What is the resistance of the wire that makes up the heating element of the toaster?
Example 2 A small electronic device (ipod?) is rated at 0.25 W when connected to 120 V. What is the resistance of this device?
ELECTRICAL CIRCUITS Flip the switch Igor!
How does Electricity Flow? Electricity moves through systems in circuits Circuits come in two styles: Series Parallel
How does electricity flow? Series Circuits In a series circuit, a direct path can be drawn from the power source through the circuit and back to the power source There is only ONE path for the electricity to flow
Circuits Series Circuit If any part of the series circuit is broken or not connected, electricity will not flow In other words, for the light to turn on, all parts must be connected and wired back to the battery
Circuits Parallel Circuits In a parallel circuit, two or more direct paths can be drawn from the power source through the circuit and back to the power source There is more than one path for the electricity to flow
Circuits Parallel Circuits If any part of the parallel circuit is broke or not connected, electricity will still be able to flow through other paths In other words, for the light to turn on, there only needs to be one path even if the others fail
Drawing Circuit Diagrams Use the table below to help draw circuit diagrams Symbol Name Symbol Name Battery Resistor Light Bulb Switch (Open) Wires Ammeter Light Bulb Switch (Closed)
Typical Capacitor
How to draw a circuit diagram Step 1: Determine what components are a part of the circuit Step 2: Start with the power source, generally on the far left of the diagram Step 3: Using straight lines to represent wires, draw wires to connect each piece of the circuit and connect back to the power source
Series Circuit
Series Circuit
Draw the circuit
Parallel Circuit
Parallel Circuit
Draw the circuit
Calculating Resistance in a Circuit Resistance in circuits is based upon the type of circuits Series Circuits 350 Ω To calculate total resistance in a series circuit, simply add all the resistors together R TOT = R 1 + R 2 + R 3 + 1260 Ω 260 Ω 175 Ω
Calculating Resistance in a Circuit Resistance in circuits is based upon the type of circuits Parallel 250 Ω 650 Ω 150 Ω To calculate total resistance in a parallel circuit, add the inverse value of all resistors together and then take the inverse of your final value