Chapter 21

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# Chapter 21 - PowerPoint PPT Presentation

An electric force of 4.5 x 10 -5 N is measured between two particles. One particle has a charge of 2.0 x 10 -6 C & the other has a charge of 3.0 x 10 -8 C. Calculate the distance between them. Chapter 21. Electric Fields.

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## Chapter 21

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An electric force of4.5 x 10-5 N is measured between two particles. One particle has a charge of2.0 x 10-6 C & the other has a charge of 3.0 x 10-8 C. Calculate the distance between them.

### Chapter 21

Electric Fields

Electric force like gravitational force is inversely proportioned to the square of the distance between the two points of concern
Electric Field (E)
• A vector quantity that relates the force exerted on a charge to the amount of the charge
Typical Field Strengths

Field Value (N/C)

TV tube 1 x 105

Spark r 3 x 106

H orbital 5 x 1011

Electric Field Lines
• Lines representing the force vectors in an electric field

Electric Field Lines

• Always point from positive to negative

Electric Field Lines

• Do not exist , but provide a model of a field

+

-

Electric Potential

• The electric potential difference of charges measured in volts

Electric Potential

• As with heat, we can only measure potential difference (DV)

Electric Potential

Difference (DV)

• The change in potential energy per unit charge

Electric Potential

Difference (DV)

• The work done moving a charge thru a field charge

Electric Potential

Difference (DV)

• Measured in J/C
• J/C = volt (V)

Electric Potential

Difference (DV)

W on q

q

DV =

Electric Potential

Difference (DV)

DU = W

Electric Potential

Difference (DV)

DUq

q

DV =

Electric Potential

Difference (DV)

W on q

q

DV =

Electric Potential

Difference (DV)

W = Fd

Electric Potential

Difference (DV)

Fd on q

q

DV =

Electric Potential

Difference (DV)

F

q

DV = x d

Electric Potential

Difference (DV)

F

q

E =

Electric Potential

Difference (DV)

DV = Ed

Basic Equations
• V = Ed
• W = qV
• F = qE

Equipotential

• When the electric potential difference is 0

Equipotential

• Charge rearranges itself to reach equipotential

Equipotential

• When two spheres have the same charge, the larger one has lower electric potential

Equipotential

• When two spheres have the same electric potential, the larger one has the greater charge

Equipotential

• When a charged object comes in contact with a neutral one, the charge is
• equally distributed

Equipotential

• Because of the size of Earth, when objects touch Earth, their charge is passed to the Earth

Grounding

• When a charged object touches Earth, all its charge flows to Earth creating equipotential

Electric Fields

• All charges are on the outside of a conductor

Electric Fields

• In pointed object, the field strength is greatest at the point

Capacitor

• A device designed to store a charge

Capacitance

• The ratio of charge to electric potential difference

• Unit for capacitance measured in coulombs per volt: F = C/V

Basic Equations

• V = Ed
• W = qV
• F = qE
• q = CV
A charge of 1.6 x 10-6 C is stored to create a capacitance of 4.0 x 10-3 F acting over 2.0 mm. Calculate: V, E, F, & W

A charge of 1.5 x 10-6 C is stored to create a capacitance of 4.0 x 10-3 F acting over 2.0 mm. Calculate: V, E, F, & W

A charge of 3.2 x 10-4 C is stored to create a capacitance of 8.0 mF acting over 4.0 mm. Calculate: V, E, F, & W

Charge =1.6 x 10-6 C

Force = 3.2 x 10-3 N

Distance = 64 nm. Calculate: V, E, C, & W