preview objectives electrical potential energy potential difference sample problem chapter 17...
TRANSCRIPT
Preview
• 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.
Section 1 Electric PotentialChapter 17
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
Section 1 Electric PotentialChapter 17
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
Chapter 17 Section 1 Electric Potential
Electrical Potential Energy
Section 1 Electric PotentialChapter 17
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
Section 1 Electric PotentialChapter 17
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
Click below to watch the Visual Concept.
Visual Concept
Chapter 17 Section 1 Electric Potential
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.
Section 2 CapacitanceChapter 17
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)
Section 2 CapacitanceChapter 17
Capacitors and Charge Storage, continued
• Capacitance is the ratio of charge to potential difference.
magnitude of charge on each platecapacitance =
potential difference
QC
V
Click below to watch the Visual Concept.
Visual Concept
Chapter 17 Section 2 Capacitance
Capacitance
Preview
• 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.
Section 3 Current and ResistanceChapter 17
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
Current and Charge Movement
• 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
Current and Charge Movement
• 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.
Current and Charge Movement
• 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)
Section 3 Current and ResistanceChapter 17
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
Section 3 Current and ResistanceChapter 17
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.
Click below to watch the Visual Concept.
Visual Concept
Chapter 17Section 3 Current and Resistance
Factors that Affect Resistance
Section 3 Current and ResistanceChapter 17
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.
Section 4 Electric PowerChapter 17
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.
Section 4 Electric PowerChapter 17
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.
Click below to watch the Visual Concept.
Visual Concept
Chapter 17 Section 4 Electric Power
Energy Transfer
Section 4 Electric PowerChapter 17
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