Concept Summary

Batesville High School Physics

Electric FieldsAn electric charge creates a

disturbance in the space around it - an electric field.

The electric field extends infinitely far but weakens with distance.

This electric field exerts a force on other charges within the field.

Electric FieldsElectric fields are vector fields.

Direction at any point is the direction that a positive charge would move if placed there.

Magnitude at any point, E = F/q Units of E are Newtons/Coulomb

Force a charge feels, F = qE

Electric Field LinesPoint in the direction a positive

charge would moveField is stronger where field lines are

closer together.Also called “lines of force”

Charged Conductors If a conductor has a static charge:

All of the charge resides on the surface of the conductor

The electric field everywhere inside the conductor is zero.

If the conductor is not spherical, the charge distribution will not be uniform.

Electric Potential EnergyYou have to do work to move a charge

in an electric field.The electric potential energy of a charge

at a point in an electric field = -(work done by the electric field when the charge is moved there).

Electric PotentialElectric potential = electric potential

energy per unit charge Electric potential, V = EPE/q Units: Joule/Coulomb

1 Volt = 1 Joule/Coulomb

Electric potential is commonly called voltage .

VoltageA location can have a voltage whether

or not a charge is located there.The voltage difference (potential

difference) between two points tells you: The energy available when a unit charge

is moved between the points, or The work that needs to be done to move

a unit charge between the two points.

VoltageThe voltage between two points

(potential difference) tells you the amount of energy 1 Coulomb of charge will lose when it moves between the two points.

Storing Electrical EnergySince unlike charges attract, it takes

work to separate unlike charges.This work is stored as electrical

potential energy

Capacitors A capacitor is a device that contains 2 parallel

conducting “plates” insulated from each other.

It is used to store electrical energy, by holding positive charges on one plate and negative charges on the other.

Capacitors can be charged to high voltages and store large amounts of energy.

Van de Graaff GeneratorThe Van de Graaff Generator is a

device for creating large voltages.Voltages of 150,000 V + are common

Voltage and DangerENERGY DOES WORK!The Van de Graaff gives each charge a

large amount of energy (high voltage), but there aren’t many charges - therefore the Van de Graaff delivers very little total energy.

Voltage and DangerAn electrical outlet (120 Volts) gives

comparatively little energy to a charge, but it can deliver LOTS of charge - at least 15 Coulombs of charge per second.

Therefore, the electrical outlet can deliver LOTS of energy - enough to kill you!

The End