Chapter 8 slideshow.notebook
Chapter 8 slideshow.notebook March 07, 2015 Unit 3 Electricity Chapter 8:Ohm’s law describes the relationship of current, voltage, and resistance. • Electric Current • Circuit Diagrams • Challenge • Homework Sep 89:31 AM Current Electricity Current electricity: is when the electrons are controlled by moving along a path together. What is voltage? Electric Potential Energy: Stored electrical energy Ex. A battery its electrons can do work after they leave the battery. Electric Potential Difference (Voltage): The change in potential energy per charge. Electrochemical cell: produces a supply of electric charge by using chemicals (a reaction occurs). 3 Parts: 2 electrodes: of different materials: often metals, an electrical conductor 1 electrolyte: often a salt, acid or base in solution, the electrolyte will conduct electricity Lets make some! Mar 48:12 AM Chapter 8 slideshow.notebook March 07, 2015 Coulomb Coulomb: the unit of electric charge. 1 coulomb = 6.25 x 1018 electrons. (added or subtracted) This is about the number of electrons that pass into a 100 W light bulb per second. Is this the true number of electrons and protons? Top of school desk Mar 148:44 AM Electric current Electric current (A):a flow of electric charge through an electrical conductor. The ampere (A) is the unit used for current This is like: two rivers of equal size and volume The river that flows faster has more water molecules flowing past a given point such as a bridge. This is a higher current. higher current Mar 148:56 AM Chapter 8 slideshow.notebook March 07, 2015 Electric circuit Electric circuit: A complete pathway that allows electrons to flow. Will transform electrical energy into other forms of energy. Mar 148:57 AM Electric circuit Parts of an electric circuit: 1) source: Where a form of energy is converted to electrical energy 2) Electrical load: Takes Electric energy and converts it into other forms of energy e.g: heat, light and sound Mar 1810:11 AM Chapter 8 slideshow.notebook March 07, 2015 Electric circuit 3) Control/switch : Opens and closes the circuit Turns circuit on and off 4) Conductor : Wires made of good conductors conducts electrons around the circuit Electric potential is provided at the source (batteries) and “used” by the circuit elements (lightbulb) (a potential or voltage drop occurs) Mar 1810:17 AM Activity Set up a working circuit Make the light bulb shine! Mar 1810:25 AM Chapter 8 slideshow.notebook March 07, 2015 Circuit Diagram Symbols • Electricians often have to draw out a circuit • Instead of drawing each part in detail, they use simple symbols Mar 149:00 AM Corrupt??? Chapter 8 slideshow.notebook March 07, 2015 Circuit Diagram Symbols Circuit diagram symbols: • bulb • cell • battery • wires • resistors • ammeter • voltmeter • open switch closed switch http://www.andythelwell.com/blobz/guide.html http://phet.colorado.edu/en/simulation/circuitconstructionkitdc http://articl319.com/shockwave/oz.htm Mar 1810:28 AM Questions 1. Label the following: 2. When the switch is opened, what happens to the electrons in the circuit? 3. Using the proper circuit symbols, draw and label a circuit that contains a single cell, a lamp, and a switch. Use arrows to indicate the flow of electrons. 4. Draw a circuit diagram for the circuit shown. Mar 1811:49 AM Chapter 8 slideshow.notebook March 07, 2015 Resistance Resistance: Slows down the flow of electrons and transforms electrical energy. Measured in ohm’s (Ω) Example: lightbulb, resistor etc Resistors: Used to control current or potential difference in a circuit. What is more difficult? • • • • Walking on sand Walking on gravel Walking on Snow Walking through water Why? This is the same for resistors. Some objects are more difficult for electrons to pass through Activity: Battery and resistance http://phet.colorado.edu/en/simulation/batteryresistorcircuit Apr 85:07 PM Resistance Factors affecting resistance: • Length: Electrons will take a longer time to pass through along wire (A long hallway will take longer to walk through) • Diameter: The thicker the wire the more electrons can pass (the wider the hallway the more students can pass) • Temperature: It is harder for electrons to move through a warm wire, easier through a cold wire (the more excited and crazy running students in a hall (warm) the harder it will be to go to class) • Type of material: Some material are good conductors of electrons, other are poor (If the hallway was made of crazy carpet or lava it would be hard to travel) Question • If you double the length of a wire, you will double the resistance of the wire. • If you double the diameter of a wire, you will cut its resistance in half. Apr 85:09 PM Chapter 8 slideshow.notebook March 07, 2015 Relationship of Voltage Resistance and Current Ohms Law: The mathematical relationship comparing voltage (V), current (I) and resistance (R) Questions: 1. Find the size of the resistor which would allow a current of 0.02A, when connected to an 8V power supply. 400Ω 2. Calculate the voltage across a 300Ω resistor when a current of 0.004A flows through it. 1.2V Activity 2: Voltage resistance and current sim: after ohms law calculation http://www.glencoe.com/sites/common_assets/science/virtual_labs/E14/E14.html http://phet.colorado.edu/sims/ohmslaw/ohmslaw_en.html Apr 85:26 PM Apr 1010:16 AM Chapter 8 slideshow.notebook March 07, 2015 Apr 1010:17 AM Conclusions Homework: Ohm's Law worksheet Labs http://phet.colorado.edu/en/simulation/circuitconstructionkitdc Apr 84:17 PM Chapter 8 slideshow.notebook March 07, 2015 Using the proper circuit symbols, draw and label a circuit that contains: a three cell battery, a lamp, and a closed switch. Use arrows to indicate the flow of electrons. Sep 89:31 AM Attachments 1206Attendance.xlsx
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