Two identical resistors are wired in series. An electrical current runs through the combination. If

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) I1 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.
R
R
R
P
Q
R
R
3
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.
B
A
4

• The four bulbs are identical. Which circuit puts
  out more total light?
• 1) I.
• Both circuits emit the
• same amount of light.
• 3) II.

Circuit II
Circuit I
12v
12v
5
The three bulbs in the circuit all have the same
resistance. Their brightness indicates the
power being dissipated by each.
A

• 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.

B
C
32v
6
3?
6?
2?

-
12v
Total effective resistance of this circuit? Total
current drawn? At what rate is the (entire)
circuit dissipating energy?
7
Answers to slides

• also I1
• decreases.
• Increases
• II.
• 4. B and C are equally bright,
• each ¼ as bright as A.

The bottom branch draws half as much current
IbottomV/(2R) compared to ItopV/R. Lets call
Ibottom I and then Itop 2I. Bulb A burns with
P(2I)2R while B or C burns Individually with
PI2R. The bottom branch as a whole has two
bulbs burning 2I2R, but we are asked to compare
each bulb.
one more slide
8
3?
6?
2?

-
12v
Total effective resistance of this
circuit? Total current drawn? At what rate is
the (entire) circuit dissipating energy?
1/Rpair 1/3? 1/6? Rtotal Rpair2 ? 4 ?
12v/4? 3 A
PIV(3 A)(12v) 36 watts