Download Lecture28 - Purdue Physics

Reading Quiz
• Which will draw more current, connecting a 9
volt battery in a circuit with a 1 Ohm
resistance or with a 100 Ohm resistance?
• 1 Ohm
• 100 Ohms
• Same current for both
Physics Help Center
Room 237 Physics Building: 8am to 5:30pm
Ask for help from graduate students on
homework and exams
Can enter solutions on the computers in the room
to check your solution.
NEXT EXAM
Wednesday April 7th @7pm to 9pm
Chapters 10,11,12,13,14,15
Summary of electric circuits:
1.
The amount of current is the same at every place in a series circuit; I=q/t.
2.
The power provided by the battery (P=IDV) is exactly equal to the power
dissipated in the resistors (P=I2R).
3.
Ohm’s Law applies to resistors: DV=IR
4.
Series circuit: effective R = R1 + R2 + R3
5.
Parallel circuit: effective R is
1
1 1
1
 

Reff R1 R2 R3
6.
Charge is conserved
7.
Current is conserved
8.
The voltage drops around a circuit is zero
Question 1
How much current I runs through this circuit?
A. 0.333 Amps
1W
1.5 V
2W
B. 0.500 A
C. 1.000 A
D. 2.250 A
E. 3.000 A
Choose the answer closest to your result.
Question 2
How much current I is generated by the battery?
A. 0.333 Amps
B. 0.500 A
1.5 V
1W
2W
C. 1.000 A
D. 2.250 A
E. 3.000 A
Choose the answer closest to your result.
Question 3
What is the voltage drop across the 2 Ohm resistor?
A. Zero
1.5 V
1W
2W
B. The same as the drop
across the other resistor.
C. More than across the
other resistor.
D. Less than across the
other resistor.
switch
Question 4:
This circuit has 2 identical light
bulbs. After the switch is closed,
+
VV
A
A. A is brighter than B.
B. A is dimmer than B.
C. A & B are equally bright, but dimmer than A was before.
D. A & B are equally bright, but brighter than A was before.
E. A & B are equally bright, and the same as A was before.
B
Question 5:
Light bulbs A, B, & C are
identical. After the switch is
closed,
switch
+
A
VV
C
A. A & C both get brighter.
B. A & C both get dimmer.
C. A is brighter, and C is dimmer.
D. A is dimmer, and C is brighter.
E. A & C stay the same.
B
Question 6
For three resistors in parallel, choose the correct statement:
A. The current and the voltage
across all three are the same.
EMF
volts
1
2
3
B. The voltage drop and the
power dissipated across all
three are the same.
C. The energy given up per
electron is the same for all
three.
D. The current through one
resistor is the same as the
current through the battery.
By placing all electric items in parallel
they receive the same voltage
By placing electrical items in series
they receive the same current
A volt meter has a high resistance so take very little current
Fig. 13.13
An Amp meter has very little resistance so take
very little voltage
Question 14
If R1=10 ohms, R2=5 ohms and R3=10 ohms
what is the total resistance of the circuit?
Energy source => Potential Energy => Kinetic Energy => Heat
Power = Energy/unit time
P=V * I
P= (I*R) *I= I2 R
Units of Power
WATTS = Joules/second
Note: Energy = power * time
We purchase electrical energy by the Kilowatt-hr
If the resistance of the light is 20 ohms what is the power given
off by the light?
If the light were to be on for 24 hours how much energy would be
used up?
Summary 5
Fig. 13.18
B
What is the current that
flows in this circuit at
point B?
1.)288 amps
2.) 1.5 amp
3.) 0.1 amp
4.) 0.5 amp
5.) 0.03 amps
.
By placing all electric items in parallel
they receive the same voltage
By placing electrical items in series
they receive the same current