Electric Hazards Lethal current 100 m A Larger

Electric Hazards • Lethal current - 100 m. A • • Larger current - 1 A • • • causes ventricular fibrillation does not stop heart causes burns Resistance of human body • • 104 - 106 when dry 103 when wet General Physics 2 Circuits 1

The Electric Battery • • Source of voltage or potential difference can make charges move! General Physics 2 Current & Resistance 2

Battery Model • • • Energy per unit charge delivered by a battery to the charge carriers it transports against the field ξ is the battery’s characteristic emf ξth is the energy per unit charge lost to thermal energy General Physics 2 Current & Resistance 3

Battery Model – con’t A chemical battery a chemical reaction to transport charge carriers to the positive electrode General Physics 2 Current & Resistance 4

Batteries in Series • The emf, ξ, of batteries connected in series, adds General Physics 2 Current & Resistance 5

Electrostatic Potential and the Roller Coaster Analogy • The potential is decreasing as it gets closer to the negative plate. General Physics 2 Current & Resistance 6

Loop Rule General Physics 2 Circuits 7

DC Circuits – Circuit Symbols Battery Capacitor Resistor Wire Switch Ground General Physics 2 Circuits 8

Symbol for battery resistor battery General Physics 2 Current & Resistance 9

Resistors circuit symbol what is the resistance of this resistor? General Physics 2 Try some others. Current & Resistance 10

Adding Resistors • In series: • In parallel: General Physics 2 Circuits 11

Resistance • Rank the configurations in order of increasing resistance. Series General Physics 2 Parallel Circuits 12

Circuit Elements in Series • General Physics 2 Circuits 13

Calculate Resistance, Current • A 12 -V battery causes a current of 0. 60 A through a resistor. (a) What is its resistance? (b) How many joules of energy does the battery lose in a minute? General Physics 2 Current & Resistance 14

Loop Rule General Physics 2 Circuits 15

Resistance, Current, Voltage • Determine (a) the equivalent resistance of the circuit, (b) the current through each resistor, and (c) the voltage across each resistor. General Physics 2 Circuits 16

Circuit Elements in Parallel General Physics 2 Circuits 17

Consider these two circuits. . . Series How does Req compare between two circuits? Parallel General Physics 2 Circuits 18

Junction Rule General Physics 2 Circuits 19

Resistance, Voltage • Determine (a) the equivalent resistance of the circuit and (b) the voltage across each resistor. General Physics 2 Circuits 20

Rank in order of brightness • • Rank bulbs 1 through 6 in order of descending brightness. • Brightness is proportional to power Now assume the filament in B 6 breaks. Again rank the bulbs in order of descending brightness. General Physics 2 Circuits 21

Practice Problems • Determine the equivalent resistance and the current through R 1 for the circuits shown. Assume R 1 = 10 , R 2 = 20 , and R 1 = 30 , and the battery is 12 V. General Physics 2 Circuits 22

E 6 - Activity • Exploration of Physics • • • E&M Resistive circuits Do each of the 5 circuits – set all to 50 ohms Calculate I, V, and P for each resistor and then check answers in the program Group Problems • E 6 B. 3, E 6 B. 4, E 6 S. 3, E 6 S. 6 General Physics 2 Current & Resistance 23