1 electric energy & potential AP

Electric vs. Gravitational

Potential Energy

• Work is needed to push an object against gravity and give it Potential Energy

Gravitational Potential Energy Increases

g

• Work is needed to push a charge against a field and give it Electric Potential Energy

Electric Potential Energy Increases

E

+-

Potential Energy & Potential Difference

Potential Difference

Voltage (scalar or vector)

What does voltage actually measure?– Measures how much

energy a charge will gain/lose

– Measures how much work that can be done by a charge

Divide both sides by qo and you get another physical quantity: Electric Potential! Otherwise known as voltage!

If the Electric Field is constant, it comes out of the integral and you get V = Ed

Uniform

Electric Fields

Allesandro Volta(Italian: 1745 – 1827)Parallel Plates

Point charge

Uniform electric field

Note the field lines

Analogy

12 V0 V

Battery gives the electron 12 J of Potential energy

e “loses” energy as it travels through the circuit.

Battery “gives” energy back to electron to repeat cycle

Potential Energy & Potential Difference

• Sample ProblemA 9 V battery is connected to two parallel plates that are separated by a distance of 0.30 cm. a. What is the electric field?b. How much energy would an electron have when placed next to the positive plate?

+ + +

–––

D = 0.04mp+

a) V = E d 9 = (E)(0.003m) E = 3000 V/m

b) Ue = q ∆V = (9 V)(1.6 x 10-19C) Ue = 1.44 x 10-18 J

Key Ideas

Flow C

hartcom

pliments of M

ike Gearon

times charge

per unit charge

times distance = Work

per unit distance

= Potential Gradient

Flow C

hartcom

pliments of M

ike Gearon

times charge

per unit charge

times distance = Work

per unit distance

= Potential Gradient