1. Pearson Prentice Hall Physical Science: Concepts in Action Chapter 20 Electricity

2. What Produces Electric Charge Def: electric charge is a property that causes subatomic particles such as protons and electrons to attract or repel each other Recall that protons are positively charges while electrons are negatively charged An excess or shortage of electrons produces a net electric charge

3. 20.1 Electric Charge & Static Electricity Objectives: 1. Explain what produces a net electric charge 2. Analyze whether an electric force is attractive or repulsive 3. Describe how to determine the strength of an electric field 4. Determine three ways in which charge is transferred 5. Explain how static discharge occurs

4. Attractive and Repulsive Like charges repel while opposite charges attract Electrons repel each other & protons repel each other Def: electric force is the force of attraction or repulsion between electrically charged objects The strength of the electric force depends on how far apart the objects are from each other The farther apart the objects are, the less strength the force has

5. How to Determine the Strength of an Electric Field Def: an electric field is the effect an electric charge has on other charges in the space around it Put another way, an electric field is the area around an object where the EF can be felt Field lines are used to show the effect due to a charge + lines go out, - lines point inward The strength of an electric field depends on the amount of charge that produces the field and on the distance from the charge EF ≈ 1/d 2 ≈ means proportional to This means if the distance is doubled, the strength decreases by ¼

6. Three Ways to Transfer Charge Charge can be transferred by friction, by contact and by induction The Law of Conservation of Charge states that the total charge in an isolated system is constant Friction: electrons are rubbed from one item to another (ex: from hair to balloon) Contact: a neutral item touches a charged item (ex: Van de Graaf) Induction: charge is transferred without direct contact between oppositely charged materials (ex: negatively charged fingers approach a positively charged doorknob)

7. Static Discharge Static discharge occurs when a pathway through which charges can move forms suddenly Lightning is an example

8. Two Types of Current Def: electric current is the continuous flow of electric charge The two types of electric current are direct current and alternating current Charge flows in only one direction in direct current (DC) Alternating current (AC) is a flow of electric charge that regularly reverses direction

9. Conductors and Insulators Def: an electrical conductor is a material through which charge can flow easily Def: an electrical insulator is a material through which charge cannot flow easily Metals such as copper and silver are good electrical conductors Materials such as wood, plastic, rubber and good electrical insulators

10. 20.2 Electric Current Objectives: 1. Name two types of current 2. Give examples of conductors and insulators 3. Describe factors that affect electrical resistance 4. Explain what causes and electric current 5. Explain how voltage, current and resistance are related

11. Electrical Resistance & Factors that affect Resistance Def: resistance is opposition to the flow of charges in a material A material’s thickness, length and temperature affect resistance Def: a superconductor is a material that has almost zero resistance when it is cooled to low temperatures

12. What Causes Electric Current In order for charge to flow in a conducting wire, the wire must be connected in a complete loop that includes a source of electrical energy Recall that potential energy is the energy of position (energy waiting to happen) Def: potential difference is the difference in electrical PE between two places in an electric field Def: voltage is electrical potential difference

13. Voltage, Current and Resistance Def: a battery is a device that converts chemical energy to electrical energy The unit of resistance is called the ohm Increasing the voltage increases the current Keeping the same voltage and increasing the resistance decreases the current