Date post: | 04-Jul-2015 |
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Education |
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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