الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

Current & Resistance
Example 7.11
Two light bulbs both operate from 110v, but one has power rating 25W
and the other of 100W. Which bulb has the higher resistance? Which
bulb carries the greater current?
Solution
Since P=V 2 /R, and V is the same for each bulb, the 25W bulb would have
the higher resistance. Since P=IV, then the 100W bulb carries the greater
current.
Example 7.12
The current I in a conductor depends on time as I=2t 2 -3t+7, where t is in
sec. What quantity of charge moves across a section through the
conductor during time interval t=2sec to t=4sec?
Solution
dQ
I = ; dQ=I dt
dt
Q =
4
2
∫ Idt = ∫ 2t
− 3t
+
2
( 7) dt
4
3 2
[ 2t
− 3t
+ 7t] = 33. C
Q =
3
2
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