preview objectives electrical potential energy potential difference sample problem chapter 17...

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• Objectives

• Electrical Potential Energy

• Potential Difference

• Sample Problem

Chapter 17 Section 1 Electric Potential

Section 1 Electric PotentialChapter 17

Objectives

• Distinguish between electrical potential energy, electric potential, and potential difference.

• Solve problems involving electrical energy and potential difference.

• Describe the energy conversions that occur in a battery.


Electrical Potential Energy

• Electrical potential energy is potential energy associated with a charge due to its position in an electric field.

• Electrical potential energy is a component of mechanical energy.

ME = KE + PEgrav + PEelastic + PEelectric


Electrical Potential Energy, continued

• Electrical potential energy can be associated with a charge in a uniform field.

• Electrical Potential Energy in a Uniform Electric Field

PEelectric = –qEdelectrical potential energy = –(charge) (electric field strength)

(displacement from the reference point in the direction of the field)

Click below to watch the Visual Concept.

Visual Concept


Electrical Potential Energy


Potential Difference

• Electric Potential equals the work that must be performed against electric forces to move a charge from a reference point to the point in question, divided by the charge.

• The electric potential associated with a charge is the electric energy divided by the charge:

V

PEelectric

q


Potential Difference, continued

• Potential Difference equals the work that must be performed against electric forces to move a charge between the two points in question, divided by the charge.

• Potential difference is a change in electric potential.

change in electric potential energy

potential differenceelectric charge

electricPEV

q


Visual Concept


Potential Difference

Preview

• Objectives

• Capacitors and Charge Storage

• Energy and Capacitors

• Sample Problem

Chapter 17 Section 2 Capacitance

Section 2 CapacitanceChapter 17

Objectives

• Relate capacitance to the storage of electrical potential energy in the form of separated charges.

• Calculate the capacitance of various devices.

• Calculate the energy stored in a capacitor.


Capacitors and Charge Storage

• A capacitor is a device that is used to store electrical potential energy.

• Capacitance is the ability of a conductor to store energy in the form of electrically separated charges.

• The SI units for capacitance is the farad, F, which equals a coulomb per volt (C/V)


Capacitors and Charge Storage, continued

• Capacitance is the ratio of charge to potential difference.

magnitude of charge on each platecapacitance =

potential difference

QC

V


Visual Concept

Chapter 17 Section 2 Capacitance

Capacitance

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• Objectives

• Current and Charge Movement

• Drift Velocity

• Resistance to Current

Chapter 17Section 3 Current and Resistance

Section 3 Current and ResistanceChapter 17

Objectives

• Describe the basic properties of electric current, and solve problems relating current, charge, and time.

• Distinguish between the drift speed of a charge carrier and the average speed of the charge carrier between collisions.

• Calculate resistance, current, and potential difference by using the definition of resistance.

• Distinguish between ohmic and non-ohmic materials, and learn what factors affect resistance.


Current and Charge Movement

• Electric current is the rate at which electric charges pass through a given area.

charge passing through a given area

electric current = time interval

QI

t


• Any flow of electric charge constitutes an electric current.

• Current itself is a measure of the rate of charge flow, and voltage measures the energy imparted to the charges. Charge flows more easily in some materials than in others.

• A net flow of electric charge constitutes an electric current.

• A current of one ampere (amp) corresponds to a flow of one coulomb per second or about 6 million trillion electrons per second


• Typical currents in household wiring range from under 1 ampere to 15 or 20 amps.

• Current moves or flows more easily in conductors, the most common being metals. In metals, the outer most electrons leave their atoms and roam freely throughout the material, creating a “sea” of electrons that can respond en masse to electric forces, and thus create electric current.


• Except in superconductors, electric charge flowing in a conductor undergoes collisions with the atoms of the material and gives up energy through heating of the material. Therefore, energy is required to force current through a conductor. This imperfect property of a conductor is described as resistance. The bigger the resistance, the more energy it will take to force charge through the conductor. This is stated mathematically in Ohm’s Law.

Ohm’s Law

V = IR

•V = voltage or potential difference•I = current (amperes)•R = resistance (measured in ohms)


Resistance to Current

• Resistance is the opposition presented to electric current by a material or device.

• The SI units for resistance is the ohm (Ω) and is equal to one volt per ampere.

• Resistance

potential difference

resistancecurrent

VR

I


Resistance to Current, continued

• For many materials resistance is constant over a range of potential differences. These materials obey Ohm’s Law and are called ohmic materials.

• Ohm’s low does not hold for all materials. Such materials are called non-ohmic.

• Resistance depends on length, cross-sectional area, temperature, and material.


Visual Concept

Chapter 17Section 3 Current and Resistance

Factors that Affect Resistance


Resistance to Current, continued

• Resistors can be used to control the amount of current in a conductor.

• Salt water and perspiration lower the body's resistance.

Resistance

• Voltage is a measure of the amount of energy imparted to charges as they move between two points. Voltage is energy in joules per coulomb of charge. For example, a 1.5 volt flashlight imparts 1.5 joules of energy to each coulomb of charge that flows from the battery through the flashlight bulb and back to the opposite terminal of the battery.

Preview

• Objectives

• Sources and Types of Current

• Energy Transfer

Chapter 17 Section 4 Electric Power

Section 4 Electric PowerChapter 17

Objectives

• Differentiate between direct current and alternating current.

• Relate electric power to the rate at which electrical energy is converted to other forms of energy.

• Calculate electric power and the cost of running electrical appliances.


Sources and Types of Current

• Batteries and generators supply energy to charge carriers.

• Current can be direct or alternating.– In direct current, charges move in a single

direction.– In alternating current, the direction of charge

movement continually alternates.


Energy Transfer

• Electric power is the rate of conversion of electrical energy.

• Electric power

P = I∆V

Electric power = current potential difference

Power and Voltage

• Power is energy per time.• Compare a 100 watt light bulb used in a 120 volt

home versus a 12 volt camper.• P = IV

• The camper must move 10 times as much charge as the house to achieve the same power.

• More power can be achieved either with a high current and low voltage or high voltage and low current.

Voltage

• Measures of voltage always involve two points such as two terminals of a battery.


Visual Concept


Energy Transfer


Energy Transfer, continued

• Power dissipated by a resistor

• Electric companies measure energy consumed in kilowatt-hours.

• Electrical energy is transferred at high potential differences to minimize energy loss.

22 ( )V

P I V I RR


Visual Concept


Relating Kilowatt-Hours to Joules

preview objectives electrical potential energy potential difference sample problem chapter 17...

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