Properties of Electric Charge

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2 Goals 2

3 Properties of Electric Charge 2 Atomic Structure: Composed of three main particles: 1. Proton 2. Neutron 3. Electron

4 Things to Remember: 3 Everything is made of atoms. Electrons can move from one atom to another atom.

5 Static Electricity The temporary building up of charge on an object. Some atoms hold e - more tightly than others. Ex. Your shoes and Carpet 4

6 If you walk across a carpet, electrons move from the rug to you (because of friction). Now you have extra electrons. Touch a door knob and ZAP! The electrons move from you to the knob. You get a shock. 5

7 6 Static electricity is actually an imbalance in the amounts of positive and negative charges in the surface of an object.

8 Three ways to induce a 7 charge in an object 1. Friction 2. Induction 3. Conduction (Contact)

9 Charging by Induction 89 Involves the charging of one object by another without direct contact.

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11 Charging by Conduction 10 involves the direct contact of a charged object to a neutral object.

12 Detecting an Electric Charge 11 An uncharged Electroscope A charged electroscope.

13 Electroscope helps detect electric charge 13

14 Electrostatics Lab

15 Electric Current 14 The constant flow of electrons.

16 Transfer of Electric Charge 15 Some materials allow electric charge to move freely: Conductors Ex: copper, aluminum Semiconductors: In their natural state they are insulators: Material can the be added material to the material to increase its conductivity Ex: Silicon and Germanium Some materials do not allow electric charge to move freely: Insulators Ex: glass, rubber Has to do with the molecular structure of

17 16 Conductors : Gold, Silver, Copper, Iron, Lead, Salt Water. Insulators : Plastics, Glass, Dry Air, Wood.

18 Voltage 17 For electrons to flow there must be a potential difference between to places. This is called voltage, which is the Push that causes electrons to flow. It s electrical Pressure. Charges flow from high voltage to low voltage. Measured in Volts (V).

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21 Current 20 The measure of how many electrons per second are flowing through the wire is the amperage (A).

22 Electrical current 21 The # of e - is called current (unit = Ampere or Amp. ) Electrical current is like the amount or volume of water flowing through the hose. Water in a Hose DC in a Wire Electrical Units pressure potential (V) Volts volume current (I) Amps friction resistance (R) Ohms

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24 Resistance 23 The tendency for a material to oppose the flow of electrons. Different material have different amounts of resistance to the flow of electrons. The unit of resistance is ohm.

25 Resistance 24 Ex: gold, silver, and copper have low resistance, which means that current can flow easily through these materials. Glass, plastics, and wood have very high resistance, which means that current cannot pass through these materials easily.

26 Resistance in Wires Thick wire Vs. Thin Wire Thin wires provide more resistance than do thick wires Resistance also depends on temperature, usually increasing as the temperature increases resistance Resistance in wires produces a loss of energy (usually in the form of heat), so materials with no resistance produce no energy loss when currents pass through them.

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28 Electric Circuits A pathway for electrons to flow. 26 Electrons follow the path of least resistance.

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30 Open Circuits 28 Electrons follow the path of least resistance

31 Electrons follow the path of least resistance Closed Circuits 28

32 Series Circuit 30 The current has only one path to follow. Electrons follow the path of least resistance

33 Parallel Circuits 31 Two or more branches for the current to flow. Electrons follow the path of least resistance

34 Lab Goals: Investigate the properties of electricity and magnetism. b) Understand the relationship among voltage, resistance & current. c) Understand how to build simple series and parallel circuits.

35 32.2 From Lab: In a series circuit the current through each of the components is the same, and the total voltage in the circuit is the sum of the voltages across each component. In a parallel circuit.. the voltage across each of the components is the same, and the total current is the sum of the currents through each component.

36 25 In a material, the current (I) is directly proportional to the voltage (V) and inversely proportional to the resistance (R). I= V OR V=IR R

37 a. What is the total voltage across the bulbs? b. What is the total resistance of the circuit? c. What is the current in the circuit? d. What is the voltage drop across each light bulb? 2A e. What happens to the brightness of each bulb in a series circuit as additional bulbs are added? Why? 2V 6V 3Ω

38 a. What is the voltage across each resistor? b. What is the current in each branch? 6 A and 4 A 12V c. What is the total current provided by the battery? 10 A The voltage is equal across all components in a parallel circuit. (Therefore, the voltage across R1 is equal to the voltage across R2 which is equal to the voltage across the battery.) The total current in the circuit is equal the sum of all individual branch currents.

39 Four identical light bulbs are connected in a circuit as shown below. The current is greatest through which of the light bulbs? A 1 B 2 C 3 D 4

40 How do batteries work? Dry Cell Batteries have three parts, an anode (-), a cathode (+), and the electrolyte. The cathode and anode (the positive and negative sides at either end of a traditional battery) are hooked up to an electrical circuit. The chemical reactions in the battery causes a build up of electrons at the anode. This results in an electrical difference between the anode and the cathode. You can think of this difference as an unstable build-up of the electrons. The electrons wants to rearrange themselves to get rid of this difference. But they do this in a certain way. Electrons repel each other and try to go to a place with fewer electrons. 33

41 34 Wet Cell -uses liquids for the electrolytes, as opposed to the dry cell

42 37 Electric Power The rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt Joule's Law

43 What is a kilowatt hour? 38 How long you run an appliance. How much energy is used? Energy used = Power (kw) x Time (hrs) E= P x t To find cost: Ex: 10 per kilowatt hour E x $

44 V are used to power an appliance that needs 15.0 amps. What is the power used? 1575 W =1.575kW How much energy is used when this appliance is used for 30.0 days- 24hrs a day? 1134 kw -hr If the power company charges 8 /Kw-h, what is the cost of the energy above. $90.72 An electric refrigerator rated 400 W operates 8 hour/day. What is the cost of energy to operate it for 30 days at 8 /Kw-h?

45 How a Lightbulb Works 35

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