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Reminder: Exam I coming up Feb 24 th !. HW3 due on Friday 21 th . “review” thing next time. I made a mistake …. The Exam: 5 Multi-choice questions ( 10 pts / ec ) 50 pts 1 or 2 Bonus M.C. questions (5pts/ ec ) 2 Written-out problems 50 pts Total 100 pts.
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Reminder:Exam Icoming up Feb 24th! HW3 due on Friday 21th . “review” thing next time I made a mistake ….
The Exam: 5 Multi-choice questions (10pts/ec) 50 pts 1 or 2 Bonus M.C. questions (5pts/ec) 2 Written-out problems 50 pts Total 100 pts
Example: 18.30 A 115-V fish-tank heater is rated at 110 W. Calculate a) the current through the heater when it’s operating, and b) its resistance.
V V
Mystery box V(t) V t
V(t) V V t
The point: Voltage sources can vary with time! Special case is sinusoidal sources: AC sources
AC current! STOP!
Measuring the average of AC values: +V0 0 -V0
+1 0 Ave = 0 -1 +1 Ave = ½ 0 -1
Measuring the average of AC values: RMS averaging 0 likewise
Ohm’s Law Peak sense Averaged sense
Example: House voltage is nominally 110 VRMS. What‘s the peak voltage?
Example: Suppose I stick an 100 resistor into a wall outlet. What peak and RMS currents will flow?
Peak power Average power
Example: What’s the average power my 100 resistor of previous example must be able to dissipate so as to not burn up? What’s the peak power?
Example: A current of 2.20 ARMS flows through a 100 W resistor. What is the average power the resistor must dissipate?
Review problem: A What’s the electric field here? (figure on next page)
Review problem: B What’s the electric potential here? (figure on next page)