Announcements EXAM 2 on Tuesday, March 17! Homework for tomorrow…

Ch. 31: CQ 11, Probs. 17, 20, & 22CQ3: 3V31.2: see whiteboard31.3: 1A, to the left31.10: 2.4 x 10-5 m

Office hours…MW 12:30-1:30 pm TR 9-10 am F 1-2 pm

Tutorial Learning Center (TLC) hours:MW 8-10 am, 12-6 pm R 8-12 pm, 2-6 pm T 8-1 pm, 2-6 pm F 8-10 am, 2-5 pm

Chapter 31

Fundamentals of Circuits(Real Batteries & Parallel Resistors)

Power dissipated by a resistor…

Resistors in series….

Terminal voltage across a real battery…

Review…

The battery current I is

1. 3 A.2. 1.5 A.3. 1 A.4. 2/3 A.5. 1/3 A.

Quiz Question 1

A real battery has an emf, E, and a terminal voltage, ΔVbat, where ΔVbat< E.

The voltage drop across the resistor R is equal to

1. E.2. ΔVbat.

3. both.4. neither.

Quiz Question 2

Notice:

ΔVR = ΔVbat , ΔVR ≠ E

31.5:Real Batteries

A 6.0Ω flashlight bulb is powered by a 3.0V battery with an internal resistance of 1.0Ω.

What are the power dissipation of the bulb and the terminal voltage of the battery?

i.e. 31.6:Lighting up a flashlight

What is the current in this circuit?

A Short Circuit…

What is the current in this circuit?

Notice:

This is the maximum possible current that this battery can produce!

A Short Circuit…

What is the short-circuit current of a 12V car battery with an internal resistance of 0.020Ω?

What happens to the power supplied by the battery?

i.e. 31.7:A short-circuited battery

Consider the circuit below, where the switch is open. The current is the same through bulbs A and B, and they are equally bright. Bulb C is not glowing.

The switch is now closed, what happens to the brightness of A?

1. It increases.2. It decreases.3. It stays the same.

Quiz Question 3

Consider two resistors in parallel… Can we find an equivalent resistor, Req, to the two

resistors, R1 & R2?

31.6:Parallel Resistors

+

-

R1 R2

+

-

Req

Consider two resistors in parallel… Can we find an equivalent resistor, Req, to the two

resistors, R1 & R2?

YES!

31.6:Parallel Resistors

Req

+

-

R1 R2

+

-

What about several resistors in parallel… Can we find an equivalent resistor, Req, to the the

resistors, R1, R2,…(all in parallel)?

31.6:Parallel Resistors

+

-

R1 R2

+

-

R3 Req

What about several resistors in parallel… Can we find an equivalent resistor, Req, to the the

resistors, R1, R2,…(all in parallel)?

YES!

31.6:Parallel Resistors

+

-

R1 R2

+

-

R3 Req

Consider the circuit below, where the switch is open. The current is the same through bulbs A and B, and they are equally bright. Bulb C is not glowing.

The switch is now closed, what happens to the brightness of A?

1. It increases.2. It decreases.3. It stays the same.ADD ADDITIONAL SLIDES! (5 MINS LEFT)

Quiz Question 3