Chapter 17 Section 1 Electric Potential 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 Chapter 17 Section 1 Electric Potential 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 Chapter 17 Section 1 Electric Potential 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 = –qEd electrical potential energy = –(charge)  (electric field strength)  (displacement from the reference point in the direction of the field)

Chapter 17 Potential Difference Section 1 Electric Potential 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:

Potential Difference, continued Chapter 17 Section 1 Electric Potential 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.

Potential Difference, continued Chapter 17 Section 1 Electric Potential Potential Difference, continued The potential difference in a uniform field varies with the displacement from a reference point. Potential Difference in a Uniform Electric Field ∆V = –Ed potential difference = –(magnitude of the electric field  displacement)

Chapter 17 Sample Problem Potential Energy and Potential Difference Section 1 Electric Potential Sample Problem Potential Energy and Potential Difference A charge moves a distance of 2.0 cm in the direction of a uniform electric field whose magnitude is 215 N/C.As the charge moves, its electrical potential energy decreases by 6.9  10-19 J. Find the charge on the moving particle. What is the potential difference between the two locations?

Sample Problem, continued Chapter 17 Section 1 Electric Potential Sample Problem, continued Potential Energy and Potential Difference Given: ∆PEelectric = –6.9  10–19 J d = 0.020 m E = 215 N/C Unknown: q = ? ∆V = ?

Sample Problem, continued Chapter 17 Section 1 Electric Potential Sample Problem, continued Potential Energy and Potential Difference Use the equation for the change in electrical potential energy. PEelectric = –qEd Rearrange to solve for q, and insert values.

Sample Problem, continued Chapter 17 Section 1 Electric Potential Sample Problem, continued Potential Energy and Potential Difference The potential difference is the magnitude of E times the displacement.

Potential Difference, continued Chapter 17 Section 1 Electric Potential Potential Difference, continued At right, the electric poten-tial at point A depends on the charge at point B and the distance r. An electric potential exists at some point in an electric field regardless of whether there is a charge at that point.

Potential Difference, continued Chapter 17 Section 1 Electric Potential Potential Difference, continued The reference point for potential difference near a point charge is often at infinity. Potential Difference Between a Point at Infinity and a Point Near a Point Charge The superposition principle can be used to calculate the electric potential for a group of charges.

Chapter 17 Section 2 Capacitance 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 Chapter 17 Section 2 Capacitance 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 Chapter 17 Section 2 Capacitance Capacitors and Charge Storage, continued Capacitance is the ratio of charge to potential difference.

Capacitors and Charge Storage, continued Chapter 17 Section 2 Capacitance Capacitors and Charge Storage, continued Capacitance depends on the size and shape of a capacitor. Capacitance for a Parallel-Plate Capacitor in a Vacuum

Capacitors and Charge Storage, continued Chapter 17 Section 2 Capacitance Capacitors and Charge Storage, continued The material between a capacitor’s plates can change its capacitance. The effect of a dielectric is to reduce the strength of the electric field in a capacitor.

Capacitors in Keyboards Chapter 17 Section 2 Capacitance Capacitors in Keyboards

Chapter 17 Energy and Capacitors Section 2 Capacitance Energy and Capacitors The potential energy stored in a charged capacitor depends on the charge and the potential difference between the capacitor’s two plates.

Chapter 17 Sample Problem Capacitance Section 2 Capacitance Sample Problem Capacitance A capacitor, connected to a 12 V battery, holds 36 µC of charge on each plate. What is the capacitance of the capacitor? How much electrical potential energy is stored in the capacitor? Given: Q = 36 µC = 3.6  10–5 C ∆V = 12 V Unknown: C = ? PEelectric = ?

Sample Problem, continued Chapter 17 Section 2 Capacitance Sample Problem, continued Capacitance To determine the capacitance, use the definition of capacitance.

Sample Problem, continued Chapter 17 Section 2 Capacitance Sample Problem, continued Capacitance To determine the potential energy, use the alternative form of the equation for the potential energy of a charged capacitor:

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.

Current and Charge Movement 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.

Chapter 17 Drift Velocity Section 3 Current and Resistance Chapter 17 Drift Velocity Drift velocity is the the net velocity of a charge carrier moving in an electric field. Drift speeds are relatively small because of the many collisions that occur when an electron moves through a conductor.

Chapter 17 Resistance to Current 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

Resistance to Current, continued 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.

Resistance to Current, continued 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. Potentiometers have variable resistance.

Chapter 17 Section 4 Electric Power 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 Chapter 17 Section 4 Electric Power 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.

Electric power = current  potential difference Chapter 17 Section 4 Electric Power Energy Transfer Electric power is the rate of conversion of electrical energy. Electric power P = I∆V Electric power = current  potential difference

Energy Transfer, continued Chapter 17 Section 4 Electric Power 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.