PHY 2049: Physics II Tutoring Center is open in room NPB 1215, M-F 12:00AM -4:00PM. It is free. Homework set for Chapter 28 has been posted.

Circuits, networks and all that Spread of information By Foot Spread of Christianity, St. Paul and his travels Buddhist missionaries By Electromagnetic waves. Connections (degrees of) Telegraph, Radio, TV, cell phones By Internet Connections

hitt A portion of a circuit is shown, with the values of the currents given for some branches. What is the direction and value of the current i? A. ↓, 6AB. ↑, 6AC. ↓, 4A D. ↑, 4AE. ↓, 2A

Electrical circuits Branches and junctions Kirchhoff's Rules All current coming to a junction equals the total current leaving the junction. (charge conservation) Around any closed loop, the total voltage drop vanishes. (work around a closed loop)

Kirchhoff’s rules Identify a branch, assign a current. All currents obey the junction rule. Identify a loop, assign a direction: A battery, V from – to + is >0 A resistor R, along the current is V = -IR Each loop gives an equation, solve for the unknowns

Circuits, Junctions Charge can not be created, nor destroyed Total Current in = Total current out i = 8A -  i

Loop calculations R 2 and R 3 are parallel. The net is in series

Not so fast 5 resistances and 3 batteries. Neither parallel nor in series. 3 braches, 2 junctions and 3 loops. i 1 + i 2 = i 3 E 1 +i 1 R 1 -i 2 R 2 - E 2 +i 1 R 1 = 0 E 1 + i 1 R 1 +i 3 R 1 - E 2 +i 3 R 1 +i 1 R 1 = 0

What is i? All V = 10 Volts and all R = 4 Ohms

What is i? All V = 10 Volts and all R = 4 Ohms? What is j? What is k? j k

What is i? All V = 10 Volts and all R = 4 Ohms j k

R = 4 Ω, V = 4 V, what is the current through R?

8 = 4I => I = 2A

Figure shows five 5.00 Ω resistors. Find the equivalent resistance between points (a) F and H and (b) F and G. (Hint: For each pair of points, imagine that a battery is connected across the pair.)