1. Ohm’s law is obeyed since the current still increases when V increases 1) Ohm’s law is obeyed since the current still increases when V increases Ohm’s law is not obeyed 2) Ohm’s law is not obeyed This has nothing to do with Ohm’s law 3) This has nothing to do with Ohm’s law V = I R linear Ohm’s law, V = I R, states that the relationship between voltage and current is linear. Thus for a conductor that obeys Ohm’s Law, the current must double when you double the voltage. ConcepTest 18.1Ohm’s Law You double the voltage across a certain conductor and you observe the current increases three times. What can you conclude? Follow-up: Where could this situation occur?

2. area is less arearadiussquared diameter of A must be two times less than B The resistance of wire A is greater because its area is less than wire B. Since area is related to radius (or diameter) squared, the diameter of A must be two times less than B. ConcepTest 18.2Wires I Two wires, A and B, are made of the same metal and have equal length, but the resistance of wire A is four times the resistance of wire B. How do their diameters compare? d A = 4 d B 1) d A = 4 d B d A = 2 d B 2) d A = 2 d B d A = d B 3) d A = d B 4) d A = 1/2 d B 5) d A = 1/4 d B

3. increases the resistancedecreases the current The voltage is provided at 120 V from the outside. The light dimmer increases the resistance and therefore decreases the current that flows through the lightbulb. ConcepTest 18.3 Dimmer When you rotate the knob of a light dimmer, what is being changed in the electric circuit? 1) the power 2) the current 3) the voltage 4) both (1) and (2) 5) both (2) and (3) Follow-up: Why does the voltage not change?

4. P = V 2 / R lower power ratinghigher resistance Since P = V 2 / R the bulb with the lower power rating has to have the higher resistance. ConcepTest 18.4 Lightbulbs Two lightbulbs operate at 120 V, but one has a power rating of 25 W while the other has a power rating of 100 W. Which one has the greater resistance? 1) the 25 W bulb 2) the 100 W bulb 3) both have the same 4) this has nothing to do with resistance Follow-up: Which one carries the greater current?

5. APHY201 11/17/2015 5 19.1 emf and Terminal Voltage   Increases the PE of charges in circuits When I = 0 then V ab = E When I > 0 then V ab = E - Ir

6. APHY201 11/17/2015 6 19.2 Resistors in Series and Parallel I = I 1 = I 2 = I 3 V = V 1 + V 2 + V 3 R eq = R 1 + R 2 + R 3   Problems with this circuit?

7. APHY201 11/17/2015 7 19.2 Resistors in Series and Parallel I = I 1 + I 2 + I 3 V = V 1 = V 2 = V 3   Advantages of this circuit? The need for fuses/circuit breakers

8. APHY201 11/17/2015 8 19.5 Capacitors in Series and Parallel SeriesParallel Q = Q 1 + Q 2 + Q 3 V = V 1 = V 2 = V 3 C eq = C 1 + C 2 + C 3 Q = Q 1 = Q 2 = Q 3 V = V 1 + V 2 + V 3

9. APHY201 11/17/2015 9 19.6 RC Circuits

10. APHY201 11/17/2015 10 19.6 RC Circuits

11. APHY201 11/17/2015 11 19.6 RC Circuits Large resistanceSmall resistance

12. APHY201 11/17/2015 12 19.8 Ammeters and Voltmeters R sh is small → I R >> I G R ser is large

13. APHY201 11/17/2015 13 19.8 Ammeters and Voltmeters Ohmmeter