Today – Continue with AC Problems Some new material from the chapter

Quiz on Friday; Exams will be returned and reviewed.

There is a new Mastering Physics Assignment that finishes the chapter.

Continue with chapter. Monday – Electromagnetic Waves – Putting it

all together.

An AC source with ΔVmax = 125 V and f = 25.0 Hz is connected between points a and d in the figure.

Calculate the maximum voltages between the following points: (a) a and b 62.8 V(b) b and c 45.6 V(c) c and d 154 V(d) b and d 108 V

What is the time average of this sine (AC) signal?

ALWAYS POSITIVE

)(cos

ry?TrigonometRemember 222 tIi

2

2

2

2

1cos

))2cos(1(2

1cos

2

22

2

2

VV

IiI

Ii

A

AA

rms

rms

What is the AMPLITUDE of the voltage that comes into your home??

120V is the ‘rms’ value. (Did you know that??)

VoltsV

VV

VV

rms

rms

170

41.11202

2

timePowerEnergytime

EnergyivPower

$$

0Power

0Power

0Power

)cos()sin()sin()cos()cos(

)cos()cos(

tIttVP

tItVP

}

Average = ZERO

)cos()sin()sin()cos()cos(

)cos()cos(

tIttVP

tItVP

)cos()cos(

22

)cos(2

1)cos()(cos2

rmsrmsVIIV

P

VItVIP

The power of a certain CD player operating at 120 V rms is 20.0W. Assuming that the CD player behaves like a pure resistance, find

(a)the maximum instantaneous power.(b)the rms current.(c)the resistance of this player.

WVI

IV

I

WattsVI

V

peakpeak

peakrms

rms

rmsrms

peak

4021202120

20

2120

20 0.167A

20

20

2120

720)167.0(

202

2

R

RIP rmsrms

A series R-L-C circuit is connected to a 120 Hz ac source that has Vrms  = 80.0 V. The circuit has a resistance of 80.0  and an impedance of 106  at this frequency.

What average power is delivered to the circuit by the source?

106

80.0 

?

754.0)cos(106

80)cos(

careswho

)cos(rmsrmsIVP

WRZ

VP

Z

R

Z

VVIP

Z

VVI

Z

VI

rms

rmsrmsrms

rmsrmsrms

rmsrms

6.45106

8080)(

)()cos(

)(

2

2

2

2

2

2