Electric Field [Autosaved]

Electric

Force Electric

FieldElectric

Potentia

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Energy

Electric

Potentia

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Electric

Potential

Differenc

eElectric

Dipoles

• Is the energetic region of space surrounding a charged object.

• Exist at a point if a force of electrical origin is exerted on charged object place at the point

• A vector quantity

• Its direction is the same as the direction of the force on a positive test charge

Test Charge (qo )

• Serves as test charge for determining the extent to which the surrounding charges generates a force

• In using this, its value in terms of magnitude should be very small,

Symbol: E

E = Fe / qo = kqqo / r2 / qo

Unit: N/C or V/m

E = kq / r2

Characteristics:

*Always directed away from positive charges and directed toward negative charges

*Provides information on the magnitude or strength of the field

- near the charge, E is strongest, electric field lines are closer

- far from charge, E is weaker, electric field lines are spread out

Characteristics:

*Do not start and stop in midspace

*The number of electric field lines leaving the positive charge or entering the negative charge is proportional to the magnitude of the charge.

*Can never cross each other

*Consider the electric field (E) produced by two or more charged particles. From the Principle of Superposition, it states

The electric field due to two or more point charges is the vector sum of the individual contributions to the field produced by each charge separately.

E = kq ȓ

r2

E = k Σ qi ȓi

r2 i

• Two charges q1 =+2.0 x 10-8 C and q2 = 3.0 x 10-8 C are 50 mm apart. What is the electric field halfway between them?

• Of a system of point charges – defined on the work that has to be done by an external agent to assemble this system of charges by bringing them to their present positions from infinity.

EPE = W = Fr = kqqo r = kqqo

r2 r

• Defined as the ratio of the potential energy (EPE) of a small test charge qo situated at that point divided by the charge itself

V = EPE = kqqo = kq

qo r2qo r

Symbol: V Unit: J/C V (Volt)

Two protons in a nucleus of U248 are 6.0 x 10-10 m apart. What is their mutual potential energy?

• The potential difference VAB between two points A and B is defined as the ratio between the work that must be done to take a charge q from A and B and the value of q.

VA – V B = EPEB – EPEA = WAB

qo qo

VA – V B = Δ(EPE) = WAB

qo qo

VA – V B = = WAB

qo

WAB = qo (VA – V B )

Symbol: V

Unit: J/C =

V (Volt)

• One electron volt is the charge in potential energy of an electron (q 1.6 x 10 C) when the electron moves through a potential difference of one electron.

• One electron volt =

• (1.60 x 10-19 C)(1.00 V) = 1.60 x 10-19 Joule• 1 Volt (eV) = 1.6 x 10-19 Joule

Equipotential Surface• A surface in which the electric potential is

the same everywhere. The easiest equipotential surfaces to visualize are those that surround on the isolated point charge. Whenever r is the same, the potential is the same and the equipotential surfaces are spherical surfaces centered on the charge. No work is required to move a charge at constant speed on an equipotential surface.

• A pair of point charges with equal magnitude and opposite sign(a positive charge +q and a negative charge –q) separated by a distance d. Example: water

• Magnitude of the product of the charges q and the separation d

• Symbol: p

p=qd

The net force on an electric dipole in a uniform external field is zero.

τ=pEsinϕ

τ=qE (dsinϕ)

U=-pE

PE for a dipole in an electric field.

Magnitude of torque in an electric dipole

• Calculate the electric dipole moment of an electron and a proton 4.30 nm apart.