Two Two identicalidentical resistors are wired in resistors are wired in seriesseries. An . An electrical current runs through the combination. If the electrical current runs through the combination. If the current through the first resistor is current through the first resistor is II11, then the current , then the current

through the second is?through the second is?

1) also 1) also II11

2) 2) II11

3) smaller than 3) smaller than II11, but not necessarily , but not necessarily II11

2

1

2

1

As more As more identicalidentical

resistors resistors RR are added are added

to the parallel circuit to the parallel circuit

shown, the total shown, the total

resistance between resistance between

points points PP and and QQ

1) increases.1) increases.

2) stays the same.2) stays the same.

3) decreases.3) decreases.

The circuit below consists of The circuit below consists of identical light bulbs burning with identical light bulbs burning with equal brightness, and a single equal brightness, and a single 1212VV battery. When the switch is battery. When the switch is closed, the brightness of bulb closed, the brightness of bulb AA

11) increases.) increases.

22) stays the same.) stays the same.

33) decreases.) decreases.

The four bulbs are identical. The four bulbs are identical. Which circuit puts out more Which circuit puts out more total light?total light?

11) ) II..

2)2) Both circuits emit the Both circuits emit the

same amount of light.same amount of light.

33) ) IIII..

The three bulbs in the circuit all have the same The three bulbs in the circuit all have the same resistance. Their brightness indicates the resistance. Their brightness indicates the powerpowerbeing dissipated by each.being dissipated by each.

1. 1. BB shines brighter than shines brighter than CC..

2. 2. BB and and CC are equally bright, are equally bright, each twice as bright as each twice as bright as AA..

3. 3. BB and and CC are equally bright, are equally bright, each half as bright as each half as bright as AA..

4. 4. BB and and CC are equally bright, are equally bright, each each ¼¼ as bright as as bright as AA..

5. All three bulbs burn with 5. All three bulbs burn with equal intensity.equal intensity.

- +

3

6 2

12v

Total effective resistance of this circuit?Total current drawn?

At what rate is the (entire) circuit dissipating energy?

1)1)also also II11

3)3)decreases.decreases.

1)1)IncreasesIncreases

3)3)IIII..

4. 4. BB and and CC are equally bright, are equally bright, each each ¼¼ as bright as as bright as AA..

Answers to slides

The bottom branch draws half as much current Ibottom=V/(2R)compared to Itop=V/R.Lets call Ibottom= I andthen Itop= 2I. Bulb Aburns with P=(2I)2Rwhile B or C burnsIndividually with P=I2R. The bottombranch as a wholehas two bulbs burning2I2R, but we are askedto compare each bulb.

one more slide

- +

3

6 2

12v

Total effective resistance of this circuit?

Total current drawn?

At what rate is the (entire) circuit dissipating energy?

12v/4 = 3 A

1/Rpair= 1/3 + 1/6Rtotal = Rpair+2 = 4

P=IV=(3 A)(12v) = 36 watts