Transcript File
Static Electricity Review 2 Types of Charge 1.(+) charge----proton 2.(-) charge----electron Basic Law of Electrostatics •Like charges repel •Opposite charges attract Electroscope • Used only to detect charge. Cannot tell type of charge. 3 Ways to charge an object: 1. Conduction--touching 2. Friction—rubbing together 3. Induction—rearrangement of charges on a neutral object, caused by a nearby charged object. Electric Field • Area surrounding a charge where the affects of the charge can be felt. • Strength depends on 2 things: 1. Size of the charge 2. Distance from the charge Conductors vs. Insulators • Conductors—allow electricity to flow through them. –Metals—copper, zinc, aluminum, etc. • Insulators—do not allow electricity to flow through them. –Non-metals—Plastic, rubber, etc. The ability to charge an object is one thing, the ability to move that charge is another. How do you “Shock” someone? Think about all of the steps!! Compare Gravitational Potential Energy to the flow of electricity: Will this ball roll down the hill without any help? WHY? Will this ball roll without any help? Why? Will this ball roll without any help? Why? In order to roll, a ball must be moving from “high ground” to “low ground”! Ball must move from high potential to low potential!!! Same with electricity. •Differences in the number of electrons will cause them to move “down the hill” •Charges move because of differences in the number of electrons. What will happen? Then what? Then what? Until when? Then what??? Electrons will continue to flow as long as there is a difference in the number of electrons!!! Potential Difference(V)—also known as Voltage ---difference in potential(# of electrons) between 2 places. ---Measured with a Voltmeter ---Measured in Volts(V) How do we keep an electric potential between 2 points?? By keeping the number of electrons higher !! By maintaining a potential difference! How though? Well what do you do when your CD Player won’t work? Or when your IPod quits? Right on!!! You change the batteries, or you charge it back up!! You force there to be a potential difference! 2 Types of batteries: 1.Dry Cell Battery—they are dry 2.Wet Cell Battery—they are wet Dry Cell Battery Wet Cell Battery Current(I) • Rate of flow of electrons –How much electricity is flowing • Measured in Amperes(A) Resistance(R) • Tendency for a material to oppose the flow of electrons – Typically, converting electric energy to thermal energy • Measured in Ohms(W) • The resistance of a material(a wire) depends on 2 things: 1. Length 2. Thickness • “Resistance controls the amount of current that flows through a circuit!!” Ohm’s Law • Current is directly proportional to the potential difference and is inversely proportional to the resistance. V=I*R What voltage is required to have a 3 A current flowing through a 5 W resistor? Given: V=I*R I = 3A V = 3 A(5 W) R=5W V = ???? V = 15 V Ex. A 9V battery is connected to a circuit. A current of 2.5 A flows through the circuit. What is the resistance of the circuit? Given: V = 9V I = 2.5A R = ???? V=I*R Ex. A hairdryer with a resistance of 400 W is connected to a common household outlet with 110 V of potential difference. How much current flows through the hairdryer? Given: R = 400 W V = 110 V I = ???? V=I*R A 3 A current flows through a circuit that has a resistance of 9 W. What voltage is required? A) B) C) D) 3V .33 V 12 V 27 V A CD player draws 5 A of current when connected to a 9 V battery. What is the resistance of the CD player? A) B) C) D) 45 W 14 W 1.8 W .56 W A 1.5 V battery is required to maintain the correct current through a 2 W circuit. What is the current through the circuit? A) 3.5 A B) 3 A C) 1.33 A D) .75 A What determines whether electricity will or will not flow? A. Current B. Potential Difference(Voltage) C. Resistance What determines how much electricity will flow? A. Current B. Potential Difference(Voltage) C. Resistance