1. ELECTRIC CURRENT AND DC CIRCUITS AP PHYSICS 1

2. ELECTRIC CURRENT

3. EXAMPLE #1 The disk drive in a CD player is connected to a battery that supplies it with a current of 0.22 A. a.How much charge passes through the drive in 4.5 s? b.How many electrons is this?

4. ELECTRIC CIRCUIT When a charge flows through a closed path and returns to its starting point. Direct Current Circuits – the flow always moves in the same direction Alternate Current Circuits - the flow of charge periodically reverses its direction

5. BATTERIES A battery provides electric potential difference to a circuit using chemical reactions to produce a difference in electric potential between its terminals. The + refers to the terminal with high electric potential The - refers to the terminal with low electric potential When the battery is connected to a circuit, electrons move from the negative terminal to the positive terminal.

6. OPEN VS CLOSED CIRCUITS Open Circuit – there is no complete loop/path through which the electrons can flow & therefore no current. Closed Circuit – there is a closed loop/complete path through which the electrons can flow.

7. ELECTROMOTIVE FORCE, EMF EXAMPLE #2 A battery with an emf of 1.5V delivers a current of 0.44A to a flashlight bulb for 64s. Find the charge that passes through the circuit and the work done by the battery.

8. OHM’S LAW EXAMPLE #3 A potential difference of 24 V is applied to a 150Ω resistor. How much current flows through the resistor?

9. RESISTIVITY Different materials provide more or less resistance than each other. Even two wires may provide different amounts of resistance based on their attributes, such as area, length, diameter or temperature. More resistanceLess resistance Higher temperatureLower temperature Smaller areaHigher area Longer lengthShorter length Smaller diameterBigger diameter

10. RESISTIVITY

11. EXAMPLE #4

12. EXAMPLE #5 A current of 1.82 A flows through a copper wire 1.75m long and 1.10mm in diameter. Find the potential difference between the ends of the wire. (ρ of copper = 1.68 x 10 -8 Ω m)

13. ELECTRICAL ENERGY & POWER

14. EXAMPLE #6 & 7 Example 6: A handheld electric fan operates on a 3.00V battery. If the power generated by the fan is 2.24W, what is the current supplied to the battery? Example 7: A battery with an emf of 12V is connected to a 545Ω resistor. How much energy is dissipated in the resistor in 65s?

15. SCHEMATIC DIAGRAMS AND CIRCUITS Schematic Diagram or Circuit Diagram: diagram which depicts the construction of an electrical circuit.

16. Since bulbs have internal resistance, sometimes bulbs are drawn as resistors in circuit diagrams and treated as resistors in calculations. Electric circuit- a set of electrical components connected so that they provide one or more complete paths for the movement of charges. Load- energy user of a circuit All complete circuits must contain a source of potential difference and a load.

17. RESISTORS IN SERIES Series- describes a circuit or portion of a circuit that provides a single conduction path without junctions. If any one bulb burns out, all of the bulbs go out because the broken filament becomes a break in the circuit. When connected in series, the current is the same in all bulbs (or resistors). The equivalent resistance (R eq ) in a series circuit is the sum of all resistances. V = I/R can be used to find current and potential difference in a series circuit.

18. SERIES PRACTICE abc a b c R:R:abc Ω:Ω: 158.04.0 1. Find the equivalent resistance of this circuit 2. A 9V battery is connected to four light bulbs. Find the equivalent resistance for the circuit & the current in the circuit.

19. EXAMPLE #8

20. RESISTORS IN PARALLEL Parallel- describes two or more components in a circuit that are connected across common points or junctions, providing separate conduction paths for the current Because of this, a bulb can burn out and will not effect any other bulbs. When connected in parallel, the potential difference is the same across all bulbs (or resistors). The equivalent resistance (R eq ) in a parallel circuit is the reciprocal sum of all resistances. V = I/R can be used to find current and potential difference in a series circuit.

21. ELEMENTS IN PARALLEL Equivalent resistance of elements connected in parallel uses inverse of each resistance R1R1 R2R2 R1R1 R2R2 R3R3 R1R1 R2R2 R3R3 R4R4

22. A 9V BATTERY IS CONNECTED TO FOUR RESISTORS. FIND THE EQUIVALENT RESISTANCE FOR THE CIRCUIT AND THE TOTAL CURRENT IN THE CIRCUIT.

23. EXAMPLE #9

24. RESISTORS IN SERIES VS. PARALLEL CircuitSeriesParallel CurrentI = I 1 = I 2 = I 3 … Current is the same for each resistor and the same as total For Total Current: I = V/R eq I = I 1 + I 2 + I 3 … Sum of currents = total current Current across a resistor: I 1 =V/R 1 and I 2 =V/R 2, etc. Potential Difference V = V 1 + V 2 + V 3 … Sum of potential differences = total potential difference. Potential difference across a resistor: V 1 = IR 1 and V 2 = IR 2,etc. V = V 1 = V 2 = V 3 … Same for each resistor and same as total Equivalent resistance R eq = R 1 + R 2 + R 3 … Sum for each resistor 1/R eq = 1/R 1 + 1/R 2 + 1/R 3 … Reciprocal sum of resistances

25. COMPLEX CIRCUITS comprised of multiple circuits Equivalent resistance can be found by decomposing a circuit a b c d e f g h

26. EXAMPLE #10 In a circuit the emf of the battery is 12V and each resistor has a resistance of 200Ω. Find: a)The current supplied by the battery b)The current through the lower two resistors

27. FIRST FIND THE RESISTANCE OF R F, R G, AND R H R:R:abcdefgh Ω:Ω: 158.09.0132.05.01214 a b c d e f g h a b c d e fgh

28. ADD R E TO R FGH R e and R fgh are set in series, so just add them up. a b c d e fgh a b c d efgh R:R:abcdefgh Ω:Ω: 158.09.0132.02.8

29. ADD R C AND R D Rc and Rd are also set up in series a b c d efgh a b cdefgh R:R:abcd Ω:Ω: 158.09.0134.8

30. ADD THE FINAL PARALLEL CIRCUIT a b cdefgh a b cdefgh R:R:abcdefgh Ω:Ω: 158.0224.8