1. Current Electricity

2. How is current produced? When a high potential is connected by a conductive material to a low potential. When a high potential is connected by a conductive material to a low potential. –Flow of electrons is called electric current. –Units: C/s = Amperes (Amps) High Potential Low Potential Equal Potential

3. When the potentials are equal, the current stops flowing When the potentials are equal, the current stops flowing –To increase the potential of the electrons an electron pump must convert (do work) another form of energy into electrical potential energy. Electron pump examples: Electron pump examples: – Voltaic or galvanic cell (dry cell) –Several cells connected (Battery) –Photovoltaic cell (solar cell) –Generator High Potential Low Potential Electron Pump

4. Two types of current Direct Current – (D.C.) Flow of electrons in only one direction Direct Current – (D.C.) Flow of electrons in only one direction –Battery Alternating Current – (A.C.) Flow of electrons at first in one direction and then the other direction. Alternating Current – (A.C.) Flow of electrons at first in one direction and then the other direction. –Generator –In your House –60 Hertz

5. What affects current flow? Potential Difference – Voltage Potential Difference – Voltage Resistance - slowing or reduction of the flow of current Resistance - slowing or reduction of the flow of current –Resistance depends on the material, length of material, and the cross sectional area of the material through which the current is moving. R is resistance,  is resistivity, L is length, A is the cross sectional area

6. Ohm’s Law Ohm’s Law stated – The ratio of V/I is a constant, where V is the voltage applied across a piece of material (such as wire) and I is the current through the material. R is the resistance of the piece of material. Ohm’s Law stated – The ratio of V/I is a constant, where V is the voltage applied across a piece of material (such as wire) and I is the current through the material. R is the resistance of the piece of material. –Units: Ohms (  ) = Volt/amp

7. Electric Power When there is current (I) in a circuit as a result of a voltage (V), the electric power (P) delivered to the circuit is: When there is current (I) in a circuit as a result of a voltage (V), the electric power (P) delivered to the circuit is:– –Units: watts = amp x volt = J/s

8. Electric Power Many electrical devices become hot when provided with sufficient electric power. Toasters, irons, space heaters, heating elements in electric stoves, and incandescent light bulbs. In such cases it is possible to obtain two equivalent power equations Many electrical devices become hot when provided with sufficient electric power. Toasters, irons, space heaters, heating elements in electric stoves, and incandescent light bulbs. In such cases it is possible to obtain two equivalent power equations When electric energy is transferred into thermal energy in a resistor, the increase in thermal energy is: When electric energy is transferred into thermal energy in a resistor, the increase in thermal energy is: –units: Kilowatt hour or Joules

9. Current in electric Circuits An electric Circuit is a closed loop. An electric Circuit is a closed loop. Basic Circuits consist of three things: Basic Circuits consist of three things: –Electron pump (Battery) –Device that reduces potential. (User) –Conducting connections (Wires)

10. Direct Current Circuits: Circuit – closed loop in which current can flow Circuit – closed loop in which current can flow Basic simple circuit Basic simple circuit –Voltage source –Voltage uses –conducting connections (wire) Diagrams for electric circuits Diagrams for electric circuits –Describe in words –use photographs/drawings –Use symbols (schematics)

11. Schematic Symbols

12. Drawing Schematic Circuits Draw symbol for battery and indicate “+” and “-“ terminals Draw symbol for battery and indicate “+” and “-“ terminals Draw wire from “+” to the voltage user and draw its symbol. Draw wire from “+” to the voltage user and draw its symbol. If a point where there are two current paths, draw connection symbol and follow one path to the user. Return to the second path and draw to its user and continue until paths join. If a point where there are two current paths, draw connection symbol and follow one path to the user. Return to the second path and draw to its user and continue until paths join. Follow path to the “-“ terminal Follow path to the “-“ terminal Check work Check work Connect ammeter in series Connect ammeter in series Connect voltmeter in parallel Connect voltmeter in parallel

13. Objectives Describe the configuration of a working circuit Describe the configuration of a working circuit Interpret circuit diagrams Interpret circuit diagrams Describe the characteristics of series connections Describe the characteristics of series connections Determine equivalent resistance of circuits having two or more resistors. Determine equivalent resistance of circuits having two or more resistors. Explain the cause of short circuits Explain the cause of short circuits Homework: Homework: –Read Pages 531-541 –Pg 534 #1-3, Pg 537 # 6-9

14. Series Circuits Only one path for current to follow Only one path for current to follow User followed by another user (ie. Resistor followed by a light) User followed by another user (ie. Resistor followed by a light) …

15. Series Circuit Rules Current is the same for each user The effective resistance is the sum of all resistors in the series –– –– The sum of the voltage drop is equal to the total voltage drop –

16. Parallel Circuits Two or more paths for current to follow Two or more paths for current to follow

17. Parallel Circuit Rules Total current in the circuit is the sum of the current in all its paths (branches) Total current in the circuit is the sum of the current in all its paths (branches) – The equivalent resistance decreases with more parallel resistors The equivalent resistance decreases with more parallel resistors – Voltage is the same in each path. Voltage is the same in each path.

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19. Objectives Describe the configuration of a working circuit Describe the configuration of a working circuit Distinguish between series and parallel circuits Distinguish between series and parallel circuits Describe the characteristics of series connections and of parallel connections. Describe the characteristics of series connections and of parallel connections. Interpret circuit diagrams Interpret circuit diagrams Determine equivalent resistance of circuits having two or more resistors. Determine equivalent resistance of circuits having two or more resistors. Explain the cause and prevention of overloading household circuits. Explain the cause and prevention of overloading household circuits. Homework: Homework: –Read Pages 531-541 –Pg 534 #1-3, Pg 537 # 6-9