Preview Objectives Electrical Potential Energy Potential Difference Sample Problem Chapter 17 Section 1 Electric Potential

Chapter 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 Potential Chapter 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 + PE grav + PE elastic + PE electric

Section 1 Electric Potential Chapter 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 PE electric = –qEd electrical 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 Potential Chapter 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:

Section 1 Electric Potential Chapter 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.

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

Chapter 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 Capacitance Chapter 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 Capacitance Chapter 17 Capacitors and Charge Storage, continued Capacitance is the ratio of charge to potential difference.

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Preview Objectives Current and Charge Movement Drift Velocity Resistance to Current Chapter 17 Section 3 Current and Resistance

Chapter 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 Resistance Chapter 17 Current and Charge Movement Electric current is the rate at which electric charges pass through a given area.

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 Resistance Chapter 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

Section 3 Current and Resistance Chapter 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 17 Section 3 Current and Resistance Factors that Affect Resistance

Section 3 Current and Resistance Chapter 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

Chapter 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 Power Chapter 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 Power Chapter 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.

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

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Section 4 Electric Power Chapter 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.

Click below to watch the Visual Concept. Visual Concept Chapter 17 Section 4 Electric Power Relating Kilowatt-Hours to Joules