Chapter 16

Electric Energy andCapacitance

1. Potential difference and Electric potential2. Point Charges3. Charge Conductors4. Equipotential Surface5. Capacitance and Capacitors

Work and Potential Energy How do I calculate

work? How do I calculate

electric potential energy?

How do I relate work with electric potential energy?

Potential Difference What is potential difference? What are its SI units? Potential difference vs. Potential

energy Potential difference for uniform

electric field

Example A proton moves a distance of 0.02m

parallel to the electric field of 200 N/C.

a) What is the work done by the proton?

b) What is the change in potential energy?

c) What is the change in potential?

Energy and Charge Movements

Basic fact For positive charge For negative charge Energy conservation

Electric Field and Electric Potential of a Point Charge

What is zero electric potential?

How do I calculate electric potential due to a point charge?

Observations

Electrical Potential Energy of Two Charges

What about Superposition principle?

How do I calculate it?

What if?

Examplesa) Find the electric potential 1.0 cm from

a proton.b) What is the potential difference

between two points that are 1 and 2 cm apart?

Examplesa) Two point charges are on the y axis,

one of magnitude 3x10-9 c at the origin and a second of magnitude 6.0 x 10-9 c at y=30 cm. Find the potential at y=60 cm.

Conductors in Equilibrium What happens to charge? What about electric field

and potential? Electric field Potential

The Electron Volt What is it? What are its units? Some comparisons

Electrons in normal atoms have energies of 10’s of eV

Excited electrons have energies of 1000’s of eV

High energy gamma rays have energies of millions of eV

Equipotentials and Electric Fields Lines – Positive Charge What is it? How about

work done? How about

electric field lines?

Dipole

Capacitance What is it? How do I find it? What are its SI units?

Parallel-Plate Capacitor Construction How does geometry

play its part? How does the charge

build up on the plates?

What does the electric field look like?

Applications of Capacitors – Computers

Computers use capacitors in many ways

Capacitors in Circuits What is a Circuit? How do you represent a circuit? How do I connect a capacitor in a

circuit? What happens when a capacitor is

connected in a circuit? What different ways can one

connect a capacitor in a circuit?

Capacitors in Parallel Total charge Potential

difference Equivalent

capacitance

Equivalent Capacitor How do I calculate

equivalent capacitance?

Capacitors in Series

How do I connect capacitors in series? What happens when capacitors are connected in series? The potential difference How do I calculate equivalent capacitance? How do I calculate the energy stored in a capacitor?

Medical Application Defibrillators

When fibrillation occurs, the heart produces a rapid, irregular pattern of beats

A fast discharge of electrical energy through the heart can return the organ to its normal beat pattern

Capacitors with Dielectrics What is a

dielectric? How does it affect

capacitance? What is dielectric

strength? Atomic view of

dielectrics

Examples

A capacitor of 4 micro farad is connected across the a 12 volt battery. What is the charge on each plate?

Examples

Two capacitors are connected in series across a 400 V power source. What is the charge on each capacitor?

Examples

Two capacitors are connected in parallel across a 400 V power source. What is the charge on each capacitor?