2. Phy2005 Applied Physics II Spring 2016 Announcements: Practice Test 1 posted on Tests page. Answers to chapter 20 problems posted on HW page Solutions to Jan. 27 problems posted Starting Today, one HITT quiz problem will be “directly” from HW

3. Science news page http://qz.com/602155/video-a- physicist-puts-his-life-on-the-line-for- the-love-of-science/ Crazy physicist Andreas Wahl – Stunt # 1

4. Last time: Capacitors Q = CV Unit of capacitance:[C] = [Q/V] = C/V= F (farad) A d C =  o A/d for a parallel plate capacitor Capacitance: measure of charge stored per unit potential difference  o : permittivity of free space 8.85 x 10 -12 F/m C = A/d oo K K: dielectric constant (material property) A d Dielectric material (insulator)

5. Today: Resistance, resistors, Ohm’s & Kichoff’s laws Reduction to equivalent capacitance C1C1 C2C2 C3C3 C eq = C 1 + C 2 + C 3 parallel series C1C1 C2C2 C3C3 1/C eq = 1/C 1 +1/C 2 +1/C 3

6. ACADEMIC HONESTY Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions.UF academic honesty policy

7. Q1: What must be the capacitance of a device that is to hold a Charge of 2  C when 1000V is connected across it? 1.5 x10 8 F 2.2 F 3.5 F 4.2 x 10 6 F 5.2 x 10 -9 F

8. - Count how many electrons are passing through this point per second. I = Ne/t [C/s = Ampere] I N electrons in t seconds

9. Current (I): amount of charge flowing through a point per unit time [I] = C/s = A (ampere) Current flows from higher potential to lower potential.  I    = R I Ohm’s law R resistor perfect wire

10. R eq Know how to reduce resistor network to “equivalent resistance”

11. Parallel connection Series connection R1R1 R2R2 R3R3 R1R1 R2R2 R3R3 R eq = R 1 + R 2 + R 3 1/R eq = 1/R 1 +1/R 2 +1/R 3 Rules are “opposite” to those for capacitors!

12. Ex. 10-1. What is the ratio of the current flowing through each resistor (I 1 :I 2 ) in the circuit? 1. 1:1 2. 3:1 3. 1:4 4. Need more info. 6 V R 1 = 10 R 2 = 30

13. ACADEMIC HONESTY Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions.UF academic honesty policy

14. Ex. 10-2. What is the ratio of the current flowing through each resistor (I 1 :I 2 )? R 1 = 10 R 2 = 30 6 V 1. 1:1 2. 3:1 3. 1:4 4. None of above

15. No potential difference along the electrical wire (assume R = 0). Electrical wires can be bent and/or stretched. A Node point (branching point) can be moved arbitrarily along the wire (but cannot cross circuit elements).