Electric Fields and Potential Notes

CP Physics

Electric Fields Space around every electric charge

acts as a force field that will interact with other charges

Can only observe a field by watching the forces it produces on other charges

Are storehouses of energy

Electric Fields, Part 2 Lines of force = lines drawn around a

charge to represent the forces experienced in its electric field (are vectors)• Stronger fields – have more lines which are

close together• Weaker fields – have fewer lines which are

farther apart

Electric Fields, Part 3 Lines of force, continued

• Length of lines indicate amount of force (longer = more force)

• Direction lines point indicate type of charge Point toward negative charges Point away from positive charges

• Lines show interaction between charges Lines always drawn from positive charges to

negative charges

Electric Fields, Part 4

A – shows electric field around a positive chargeB – shows the electric field interactions between a positive charge and a negative chargeC – shows the electric field that exists between a positively charged plate and a negatively charged plate

Electric Shielding Charges spread out over a

conductor’s surface so that the electric field inside it is zero

True reason car is safest place in a thunderstorm: if hit by lightning, the charges spread out over the car’s surface and inside the car you experience zero electric force

Electrical Potential Energy Energy a charge possesses because

of its location (as compared to other charges)

Separating a positive charge from a negative charge – increases potential energy because you must do work against their attraction

Pushing like charges together – increases potential energy because you must do work against their repulsion

Electric Potential Electrical potential energy per charge Also known as potential difference (or

voltage) Unit = volt (V) (1 volt = 1 J/C) Can create large voltages, but if only a few

charges, then very low potential energy High voltages require great amount of

energy only if there is a great amount of charged involved (1 C = large amount of charge)

Capacitors Found in nearly all electronic circuits Store electrical energy Made of two metal plates that store

energy from the battery in an electric field between the two plates

Fully charged when voltage equals the battery voltage

Discharges when path provided between plates

Ex. Used in camera flashes

Van de Graff Generators Device to build up high voltages Charges move up insulator belt inside

generator and move to outside surface – field inside generator is always zero

Charges continuously move up to dome of generator

High electric potential can result