Electrical Potential Energy 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 + PEgrav + PEelastic + PEelectric

Electrical Potential Energy, continued 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 PEelectric = –qEd electrical potential energy = –(charge)  (electric field strength)  (displacement from the reference point in the direction of the field)

Electrical Potential Energy Section 1 Electric Potential Chapter 17 Electrical Potential Energy

Chapter 17 Potential Difference 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:

Potential Difference, continued 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.

Section 1 Electric Potential Chapter 17 Potential Difference

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

Potential Difference, continued Section 1 Electric Potential Chapter 17 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 Section 1 Electric Potential Chapter 17 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.

Superposition Principle and Electric Potential Section 1 Electric Potential Chapter 17 Superposition Principle and Electric Potential

Capacitors and Charge Storage 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)

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

Section 2 Capacitance Chapter 17 Capacitance

Capacitors and Charge Storage, continued Section 2 Capacitance Chapter 17 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 Section 2 Capacitance Chapter 17 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 Section 2 Capacitance Chapter 17 Capacitors in Keyboards

Parallel-Plate Capacitor Section 2 Capacitance Chapter 17 Parallel-Plate Capacitor

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

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

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.

Section 3 Current and Resistance Chapter 17 Conventional Current

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.

Section 3 Current and Resistance Chapter 17 Drift Velocity

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.

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

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.

Sources and Types of Current 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.

Electric power = current  potential difference 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

Section 4 Electric Power Chapter 17 Energy Transfer

Energy Transfer, continued 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.

Relating Kilowatt-Hours to Joules Section 4 Electric Power Chapter 17 Relating Kilowatt-Hours to Joules