Download Slide 1

Two identical resistors are wired in series.
An electrical current runs through the
combination. If the current through the
first resistor is I1, then the current through
the second is?
1) also I1
2)
1
I1
2
1
3) smaller than I1, but not necessarily I1
2
As more identical
resistors R are added
to the parallel circuit
shown, the total
resistance between
points P and Q
1) increases.
2) stays the same.
3) decreases.
The circuit below consists of
identical light bulbs burning
with equal brightness, and a
single 12V battery. When the
switch is closed, the
brightness of bulb A
1) increases.
2) stays the same.
3) decreases.
The four bulbs are identical.
Which circuit puts out
more total light?
1) I.
2) Both circuits emit the
same amount of light.
3) II.
The three bulbs in the circuit all have the same
resistance. Their brightness indicates the power
being dissipated by each.
1. B shines brighter than C.
2. B and C are equally bright,
each twice as bright as A.
3. B and C are equally bright,
each half as bright as A.
4. B and C are equally bright,
each ¼ as bright as A.
5. All three bulbs burn with
equal intensity.
3
6
2
+
-
12v
Total effective resistance of this circuit?
Total current drawn?
At what rate is the (entire) circuit
dissipating energy?
Answers to slides
1)also I1
3)decreases.
1)Increases
3)II.
4. B and C are equally bright,
each ¼ as bright as A.
one more slide
The bottom branch
draws half as much
current Ibottom=V/(2R)
compared to Itop=V/R.
Lets call Ibottom= I and
then Itop= 2I. Bulb A
burns with P=(2I)2R
while B or C burns
Individually with
P=I2R. The bottom
branch as a whole
has two bulbs burning
2I2R, but we are asked
to compare each bulb.
3
6
2
+
-
12v
Total effective resistance of this circuit?
1/Rpair= 1/3 + 1/6
Rtotal = Rpair+2  = 4 
Total current drawn? 12v/4 = 3 A
At what rate is the (entire) circuit
dissipating energy? P=IV=(3 A)(12v) = 36 watts