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# Announcements - PowerPoint PPT Presentation

Announcements. Homework for tomorrow… (Ch . 31, CQ8, Probs. 10, 17, & 42) 30.29: Tungsten 30.32: 2.3 x 10 -3 A 30.54: (4.0 μ s )(1 – e - t /2.0 μ s ) Office hours… MW 12:30-1:30 pm TR 9-10 am F 10-11 am Tutorial Learning Center (TLC) hours:

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Presentation Transcript
Announcements
• Homework for tomorrow…

(Ch. 31, CQ8, Probs. 10, 17, & 42)

30.29: Tungsten

30.32: 2.3 x 10-3 A

30.54: (4.0 μs)(1 – e -t/2.0μs)

• Office hours…

MW 12:30-1:30 pm

TR 9-10 am

F 10-11 am

• Tutorial Learning Center (TLC) hours:

M 8-1 pm, 3-6 pm, W 8-1 pm, 2-6 pm

TR 8-6 pm, F 8-2 pm

### Chapter 31

Fundamentals of Circuits

(Series Resistors & Real Batteries)

Review…

Rate at which the battery supplies energy to the charges is..

31.3:Energy and Power

Power dissipated by a resistor..

31.3:Energy and Power

Power dissipated by a resistor..

Notice:

For resistors in series, the resistor with the largest resistance dissipates the most power.

Quiz Question 1

Which resistor dissipates more power?

• The 9  resistor.
• The 1  resistor.
• They dissipate the same power.
i.e. 31.4:The Power of Sound

Most loudspeakers are designed to have a resistance of 8Ω.

If an 8Ω loudspeaker is connected to a stereo amplifier with a rating of 100W, what is the maximum possible current to the loudspeaker?

Kilowatt Hours

The energy dissipated by a resistor during time interval Δtis

1 kWh is equivalent to how many J’s?

Quiz Question 2

How does the brightness of bulb B compare to that of bulb A?

• Bulb B is brighter.
• Bulb A is brighter.
• Both bulbs have the same brightness.
31.4:Series Resistors

Consider two resistors in series…

• Can we find an equivalent resistor, Req, to the two resistors, R1 & R2?

R1

+

+

Req

-

-

R2

31.4:Series Resistors

Consider two resistors in series…

• Can we find an equivalent resistor, Req, to the two resistors, R1 & R2?
• YES!

R1

+

+

Req

-

-

R2

31.4:Series Resistors

What about several resistors in series…

• Can we find an equivalent resistor, Req, to the resistors, R1, R2,…(all in series)?

R1

+

+

R2

Req

-

-

R3

31.4:Series Resistors

What about several resistors in series…

• Can we find an equivalent resistor, Req, to the resistors, R1, R2,…(all in series)?
• YES!

R1

+

+

R2

Req

-

-

R3

Series Resistors
• A battery provides a fixed emf(potential difference), NOT a fixed current.
• The amount of current depends on…
• the battery’s emf
• the resistance of the circuit attached to the battery.
i.e. 31.5:A series resistor circuit
• What is the current in the circuit below?
• Draw a graph of potential versus position in the circuit, going cw from V = 0V at the battery’s negative terminal.
Ammeters…
• are used to measure currents.
• Must be wired in series with the circuit element whose current is to be measured.
• Rammeter~0 Ω
31.5:Real Batteries
• have an internal resistance, r
• The terminal voltage is…

Notice:

• only when I = 0, is .