The document provides information about electrical energy, potential difference, capacitance, current, resistance, and power. It defines key concepts such as volts, capacitance, resistance, Ohm's Law, electric current, direct current, alternating current, and electric power. It also includes examples of calculating charge, energy, current, resistance, and power using given values and equations.

1. +
Electrical Energy and Currents
Chapter 17
Pg. 592-625

2. +
17.1 Electric Potential
Pg. 594-601

3. +
What do you think?
• You may have purchased batteries for
radios, watches, CD players, and other electronic
devices. Batteries come in a variety of different
sizes and voltages. You probably have 1.5 volt, 3
volt, and 12 volt batteries in your home.
• What do volts measure?
• Is the number of volts related to the size of the
battery?
• How is a 3 volt battery different from a 1.5 volt
battery?

4. +
Electric Potential Energy
 Potentialenergy associated with a charge
due to its position in an electric field
 Electrical
potential energy is a component of
mechanical energy
 M. E. is conserved so long as friction and
radiation are not present
 Electrical
potential energy can be associated
with a charge in a uniform field

5. +
Electrical Potential Energy
 A uniform
electric field exerts a force on a
charged particle moving it from A to B.
 Will
the particle shown gain or lose
PEelectricas it moves to the right?
 Lose energy (because it is moving with the
force, not against it)
 Similar to a falling object losing PEg
 PEelectric = Wdone = Fd = -qED

6. +
Electrical Potential Energy
 PEelectric is positive if the charge is negative and
moves with the field.
 PEelectric is positive if the charge is positive and
moves against the field.

7. +
Classroom Practice Problem
 A uniformelectric field strength of 1.0 x 106
N/C exists between a cloud at a height of 1.5
km and the ground. A lightning bolt transfers
25 C of charge to the ground. What is the
change in PEelectric for this lightning bolt?
 d= 1,500m q= 25C
 E= 1.0 X 106 N/C PEelectric= ??

8. +
Classrom Practice Problem
 PEelectric = -qEd
 PEe= (-25)(1.0 X 106)(1500)
 Answer: -3.75 x 1010 J of energy

9. +
Potential Difference
 Potential difference( V) is the change in
electrical potential energy per coulomb of
charge between two points.
 Depends on the electric field and on the initial and
final positions
 Does not depend on the amount of charge
 SI unit: joules/coulomb (J/C) or Volts (V)

10. +
Potential Difference
 Thepotential difference is calculated
between two points, A and B.
 The field must be uniform.

11. +
Batteries
 A battery
maintains a constant potential difference
between the terminals.
 1.5 V (AAA, AA, C and D cell) or 9.0 V or 12 V (car)
 In1.5 V batteries, the electrons use chemical
energy to move from the positive to the negative
terminal.
 They gain 1.5 joules of energy per coulomb of charge
 When connected to a flashlight, the electrons move
through the bulb and lose 1.5 joules of energy per
coulomb of charge.
 Sort of like a concentration gradient.

12. +
Now what do you think?
 You may have purchased batteries for
radios, watches, CD players, and other electronic
devices. Batteries come in a variety of different
sizes and voltages. You probably have 1.5 volt, 3
volt, and 12 volt batteries in your home.
 What do volts measure?
 Is the number of volts related to the size of the
battery?
 How is a 3 volt battery different from a 1.5 volt
battery?

13. +
17.2 Capacitance
Pg 602- 607

14. +
What do you think?
• If a light bulb replaced the two metal plates and the
battery was connected, electrons would flow out of
the negative and into the positive terminal. Will this
also occur with the two metal plates?
• If not, why not?
• If so, is the flow similar or different from that with the light
bulb? Explain.
• The battery shown has a
potential difference of 6.0 volts. It
has just been connected to two
metal plates separated by an air
gap. There is no electrical
connection between the two
plates and air is a very poor
conductor.

15. +
Capacitors
 A device that is used to store PEelectric
 The two metal plates are electrically neutral
before the switch is closed. What will happen
when the switch is closed if the left plate is
connected to the negative terminal of the
battery?
 Electrons will flow toward lower PE.
 From the battery to the left plate
 From the right plate to the battery

16. +
Parallel Plate Capacitors
 Electrons build up on the left plate, giving it a
net negative charge. The right plate has a
net positive charge.
 Capacitors can store charge or electrical PE.

17. +
Capacitance
 Capacitance measures the ability to store charge.
 SI unit: coulombs/volt (C/V) or farads (F)
 In what way(s) is a capacitor like a battery?
 In what way(s) is it different?

18. +
Capacitance
 How would capacitance change if the metal
plates had more surface area?
 Capacitance would increase.
 How would it change if they were closer
together?
 Capacitance would increase.

19. +
Dielectrics
 The space between the plates is filled with a
dielectric.
 Rubber, waxed paper, air
 The dielectric increases the capacitance.
 Theinduced charge on the dielectric allows more
charge to build up on the plates.

20. + Capacitor Applications
 Connecting the two plates of a charged
capacitor will discharge it.
 Flash
attachments on cameras use a charged
capacitor to produce a rapid flow of charge.
 Some computer keyboards use capacitors
under the keys to sense the pressure.
 Pushingdown on the key changes the
capacitance, and circuits sense the change.

21. +
Energy and Capacitors
 Asthe charge builds, it requires more and more
work to add electrons to the plate due to the
electrical repulsion.
 The average work or PE stored in the capacitor is
(1/2)Q V.
 Derive equivalent equations for PEelectric by
substituting:Q= C V and V = Q/C

22. +
???? Classroom Practice Problem
 A 225 F is capacitor connected to a 6.00
V battery and charged. How much charge
is stored on the capacitor? How much
electrical potential energy is stored on the
capacitor?
 Answers: 1.35 x 10-3 C , 4.05 x 10-3 J

23. +
Now what do you think?
 Ifa light bulb replaced the two metal
plates and the battery was connected,
electrons would flow out of the negative
and into the positive terminal. Will this
also occur with the two metal plates?
 If not, why not?
 If so, is the flow similar or different from that
with the light bulb? Explain.

24. +
17.3 Current and Resistance
Pg 608-617

25. +
What do you think?
• The term resistance is often used when
describing components of electric
circuits.
• What behavior of the components
does this term describe?
• Do conductors have resistance?
• If so, are all conductors the same?
Explain.
• What effect would increasing or
decreasing the resistance in a circuit
have on the circuit?

26. +
Electric Current
 Electric
current (I) is rate at which charges flow
through an area.
 SI unit: coulombs/second (C/s) or amperes (A)
1A= 6.25 1018 electrons/second

27. +
Conventional Current
 Conventional current (I) is defined as the
flow of positive charge.
 The flow of negative charge as shown would be
equivalent to an equal amount of positive charge in
the opposite direction.
 In conducting wires, I is opposite the
direction of electron flow.

28. +
Resistance to Current
 Resistance is opposition to the flow of charge.
 SI unit: volts/ampere (V/A) or ohms ( )
 Ohm’s Law : V = IR
 Valid
only for certain materials whose resistance is
constant over a wide range of potential differences

29. +
Classroom Practice Problems
 A typical100 W light bulb has a current of
0.83 A. How much charge flows through the
bulb filament in 1.0 h? How many electrons
would flow through in the same time period?
 Given:
 I= 0.83A t= 1 hour= 3600 seconds
 Q= ?? C electrons= ??

30. +
Classroom Practice Problems
 I= Q/t or Q= It
 Q= (0.83)(3600)
 2988 C
 We know that 1 A = 6.25 1018 electrons/second
 2988 C x (6.25 x 1018 electrons/C)
 1.87 x 1022electrons

31. +
Classroom Practice Problems
 This same 100 watt bulb (from the previous
question) is connected across a 120 V potential
difference. Find the resistance of the bulb.
 Given:
 V= 120V I= 0.83A R= ?? Ω
R = V/I
 120 V / 0.83 A
 144.6

32. +
Resistance of a Wire
 On the next slide, predict the change
necessary to increase the resistance of a
piece of wire with respect to:
 Length of wire
 Cross sectional area or thickness of the
wire
 Type of wire
 Temperature of the wire

33. +

34. +
Applications
 Resistors in a circuit can change the current.
 Variableresistors (potentiometers) are used in
dimmer switches and volume controls.
 Resistors on circuit boards control the current
to components.
 Thehuman body’s resistance ranges from
500 000 (dry) to 100 (soaked with salt
water).
 Currents under 0.01 A cause tingling.
 Currents greater than 0.15 A disrupt the heart’s
electrical activity.

35. +
Now what do you think?
• The term resistance is often used when
describing components of electric circuits.
• What behavior of the components
does this term describe?
• Do conductors have resistance?
• If so, are all conductors the
same? Explain.
• What effect would increasing or
decreasing the resistance in a
circuit have on the circuit?

36. +
17.4 Electric Power
Pg. 618-623

37. +
What do you think?
• Hair dryers, microwaves, stereos, and other
appliances use electric power when plugged into
your outlets.
• What is electric power?
• Is electric power the same as the power discussed
in the chapter “Work and Energy?”
• Do the utility companies bill your household for
power, current, potential difference, energy, or
something else?
• What do you think is meant by the terms alternating
current (AC) and direct current (DC)?
• Which do you have in your home?

38. +
Types of Current - Direct
 Batteriesuse chemical energy to give electrons
potential energy.
 There is a potential difference across the terminals
 Chemical energy is eventually depleted.
 Electrons always flow in one direction.
 Called direct current (DC)

39. +
Types of Current - Alternating
 Generators change
mechanical energy into
electrical energy.
 Falling water or moving steam
 Electrons vibrate back and
forth.
 Terminals switch signs 60 times
per second (60 Hz).
 Called alternating current (AC)
 AC is better for transferring
electrical energy to your home.

40. +
Energy Transfer
 Is
the electrical potential energy
gained, lost, or unchanged as the
electrons flow through the following
portions of the circuit shown:
 A to B
 B to C
 C to D
 D to A
 Explain your answers.

41. +
Energy Transfer
 A to B (unchanged)
 B to C (lost in bulb)
 C to D (unchanged)
 D to A (gained in battery)

42. +
Electric Power
Click below to watch the Visual Concept.
Visual Concept

43. +
Electric Power
 Power is the rate of energy consumption ( PE/ t ). For
electric power, this is equivalent to the equation shown
below.
 SI unit: joules/second (J/S) or watts (W)
 Current (I) is measured in amperes (C/s).
 Potential difference ( V) is measured in volts (J/C).
 Substitute using Ohm’s law ( V = IR) to write two other
equations for electric power.

44. +
Classroom Practice Problems
 A toasteris connected across a 120 V kitchen
outlet. The power rating of the toaster is 925 W.
 What current flows through the toaster?
 Given:
 V= 120v P= 925W I= ??A
I = P/ V
 925 W / 120 V
 7.7 A

45. +
Classroom Practice Problems
 What is the resistance of the toaster?
 V= 120v I= 7.7A R= ??
R = V/I
 120 V/ 7.7 A
 16

46. +
Classroom Practice Problems
 How much energy is consumed in 75.0 s?
 Energy =P t
 P= 925 W t= 75 sec Energy=??
 (925 W)(75.0 s)
 6.94 104 J

47. +
Household Energy Consumption
 Power companies charge for energy, not
power.
 Energy consumption is measured in
kilowatt•hours
( kw•h).
 The joule is too small.
 A kw•h is one kilowatt of power for one hour.
 Examples of 1 kw•h:
 10 light bulbs of 100 W each on for 1 h
 1 light bulb of 100 W on for 10 h
1 kw•hr = 3 600 000 J or 3.6 x 106 J

48. +
Electrical Energy Transfer
 Transfer
of energy from power plants to your
neighborhood must be done at high voltage
and low current.
 Power lost in electrical lines is significant.
 P = I2R
 Power lines are good conductors but they are
very long.
 Since power companies can’t control the
resistance (R), they control the current (I) by
transferring at high voltage.

49. +
Now what do you think?
 Hair dryers, microwaves, stereos, and other
appliances use electric power when plugged
into your outlets.
 What is electric power?
 Is electric power the same as the power
discussed in the chapter “Work and Energy?”
 Do the utility companies bill your household for
power, current, potential difference, energy, or
something else?
 What do you think is meant by the terms
alternating current (AC) and direct current (DC)?
 Which do you have in your home?

50. +
NOT NEEDED??? Gravitational
Potential Difference
 Suppose a mass of 2.00 kg is moved from point A straight
up to point B a distance of 3.00 m. Find the PEg for the
mass if g = 9.81 m/s2. Repeat for a mass of 5.00 kg.
 Answer: 58.9 J and 147 J
 What is the PEg per kg for each?
 Answer: 29.4 J/kg for both
 The change per kg does not depend on the mass. It
depends only on points A and B and the field strength.
 There is an analogous concept for electrical potential
energy, as shown on the next slide.