1. AP PHYSICS Circuits

2. CAUTION! Do not leave any circuit connected longer than necessary to observe bulb brightness. Leaving a circuit connected for too long can ruin the battery (and is not environmentally friendly).

3. Stuff to do Make a bulb light with 1 bulb, 1 battery, and 1 wire What do we need to make the bulb light? What doesn’t work? Complete Circuits

4. Stuff 2 do Conductors and Insulators Look inside a bulb – what is connected to which other parts? How is this similar to a complete circuit idea from before?

5. Stuff 3 do Flashlights Switches

6. What does it all mean? Electrons are travelling through the conductors The more electrons pass by every second, the more brightness we see in the bulb. We call this CURRENT = rate of charge past a point How can we tell how much current there is?

7. Series and Parallel Put 2 bulbs in a row connected to the same # of batteries. How does the brightness change? What will happen with 3 in a row? Why do you think this happens? Bulbs in a row are called SERIES

8. Parallel Put two bulbs in PARALLEL (as shown on the board). What happens to their brightness compared to before? What about the total current? Can we tell for sure? How do we test this? The splits in the wires before parallel bulbs are called JUNCTIONS

9. Total Current See section 3… Models of electric circuits!

10. Circuit Parts Battery – Voltage – Potential Difference Wire – just a connection, path of conductors Bulb – Resistance and Brightness (current) Other Resistors

11. Diagrams Circuit Diagrams: Battery Wire Bulb Capacitor Resistor (other than a bulb) Diode/LED

12. More Stuff Fuses AC/DC Current - Drift velocity vs. velocity of an electron http://www.stmary.ws/highschool/physics/home/animations3/electricity/electrons_conductivity.html

13. meters Charge is said to flow THROUGH a circuit Current is said to be THROUGH a bulb Voltage is said to be placed ACROSS a circuit Voltage can be calculated ACROSS a battery Why? (hint: what are the definitions of the two words) How do we measure current and voltage?

14. Meters What are we measuring? Ammeter- # electrons passing by per second Voltmeter – potential difference between 2 points

15. Ohm’s Law George Simon Ohm – 1789 – 1854 Taught math Most physicists did not use math, just observed He combined observations and math Ohm’s Law V = IR

16. Questions How much current is drawn by a lamp that has a resistance of 60 Ω when a voltage of 12 V is impressed across it? What is the resistance of an electric frying pan that draws 12 A when connected to a 120 V circuit?

17. Kirchhoff’s First Rule Kirchhoff’s First Rule:  The total current out of a node is equal to the total current into the node.  (current in = current out)  i 1 + i 2 = i 3 + i 4 +i 5  The algebraic sum of the currents at a node is zero.  i 1 + i 2 – i 3 –i 4 –i 5 = 0

18. Resistances Resistors in parallel add together like this:  1/R T = 1/R1 + 1/R2 + 1/R3 + …. Resistors in a row (series) add together  R T = R1 + R2 + R3 +…

19. Rules for Circuit Analysis Redraw the circuit – resistors in series and parallel Simplify – combine each set of series and parallel Find Req for the entire circuit Find I total – current though the battery Use Kirchoff’s Law to find other I values