Fields 3: Electric Potential Energy

How does electric potential energy compare to gravitational potential energy?

• A gravitational field acts between two masses– Work done against a gravitational field

• Increases PE

– Work done by a gravitational field• Decreases PE

How does electric potential energy compare to gravitational potential energy?

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• An electric field acts between two charges– Work done against an electric field

• Increases PE

– Work done by an electric field• Decreases PE

For each of the following: does PE increase or decrease?

• Opposite charges are brought together:

For each of the following: does PE increase or decrease?

• Opposite charges are brought together: Decrease• Like charges are moved apart:

For each of the following: does PE increase or decrease?

• Opposite charges are brought together: Decrease• Like charges are moved apart: Decrease• Like charges are brought together:

For each of the following: does PE increase or decrease?

• Opposite charges are brought together: Decrease• Like charges are moved apart: Decrease• Like charges are brought together: Increase• Opposite charges are moved apart:

For each of the following: does PE increase or decrease?

• Opposite charges are brought together: Decrease• Like charges are moved apart: Decrease• Like charges are brought together: Increase• Opposite charges are moved apart: Increase

What is electric potential difference?

• The change in PE per unit charge.– How can it be calculated?

What is a volt?

• Unit for electric potential energy (potential difference.)

• Joules of energy required to move 1c between two points in an electric field.

• Measured with a voltmeter

What is a volt?

Ex) 27J of work are required to move a charge of 3c, What is the voltage?

What is an electron-volt?

• Another unit for work

• The energy required to move 1 electron (or proton) through a potential difference of 1 volt.

1ev = 1.60x10-19J (in reference table)

Electron Volt

• Ex) What quantity is equivalent to 4.8x10-17 joules?

a) 4.8 ev

b) 4.8x10-17 ev

c) 300 ev

d) 480 ev

Electric Potential difference in a Uniform Field

The electric field intensity between two large, charged, parallel metal plates is 6000 N/c. The

plates are 0.05 m apart.

• What is the electric potential difference between them?

• The electric field intensity between two parallel plates is 4.0x104 N/c. If the plates are separated by 5.0x10-3 m, what is the potential difference of the plates?

a) 3.0x104 volts

b) 200 volts

c) 8.0x106 volts

d) 120 volts

Example

Which has the greater Electric Potential Difference

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Which has the greater Electric Potential Difference

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