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ELECTRIC FIELDANAS MUQODDASMASLAHATUL UMMAH

Gravitational Fieldsurrounding any object with mass, or collection of objects with mass, is a gravitational field. Any mass placed in a gravitational field will experience a gravitational force. We defined the field strength as the gravitational force per unit mass on any test mass placed in the field: g = F / m. g is a vector that points in the direction of the net gravitational force.EarthmF2Electric FieldSurrounding any object with charge, or collection of objects with charge, is a electric field. Any charge placed in an electric field will experience a electrical force. We defined the field strength as the electric force per unit charge on any test charge placed in the field: E = F / q. E is a vector that points, , by definition, in the direction of the net electric force on a positive charge.-qF+Electric & Gravitational Fields ComparedField strengthForceIntrinsic PropertySI unitsg =W/mN / kgE=FE/qN / CGravity:Electric Force:4The Magnitude of E-FieldThe magnitude of the electric field intensity at a point in space is defined as the force per unit charge (N/C).Like the electric force, the electric field E is a vector. If the electric field at a particular point is known, the force a charge q experiences when it is placed at that point is given by : Electric Field Intensity E

Electric FieldConsider a test charge +q placed at P a distance r from Q.The outward force on +q is:

The electric field E is therefore:

+++++ +++Q.rPE

The Resultant Electric Field.The resultant field E in the vicinity of a number of point charges is equal to the vector sum of the fields due to each charge taken individually. Consider E for each charge.

Vector Sum:E = E1 + E2 + E3Directions are based on positive test charge.Magnitudes are from:

+-q1q2q3-AE3E2ERE1Electric Field Lines

Electric Field Lines are imaginary lines drawn in such a way that their direction at any point is the same as the direction of the field at that point.

Field lines go away from positive charges and toward negative charges.

Examples of E-Field Lines

Two equal but opposite charges.Two identical charges (both +).The field around a charged conductorA conductor is in electrostatic equilibrium when the charge distribution (the way the charge is distributed over the conductor) is fixed. At equilibrium, the charge and electric field follow these guidelines: the excess charge lies only at the surface of the conductor the electric field is zero within the solid part of the conductor the electric field at the surface of the conductor is perpendicular to the surface charge accumulates, and the field is strongest, on pointy parts of the conductor Charged ConductorGaussian Surface just inside conductorElectric fluxElectric flux is a measure of the number of electric field lines passing through an area. To calculate the flux through a particular surface, multiply the surface area by the component of the electric field perpendicular to the surface. If the electric field is parallel to the surface, no field lines pass through the surface and the flux will be zero. The maximum flux occurs when the field is perpendicular to the surface.The electric flux is equal to (E cos) A, where is the angle between the electric field and the normal (the perpendicular) to the surfaceA clever way to calculate the electric field from a charged conductor is to use Gauss' Law. Gauss' Law can be tricky to apply, though, so we won't get into that. What we will do is to look at some implications of Gauss' Law. It's also a good time to introduce the concept of flux. This is important for deriving electric fields with Gauss' Law, which you will NOT be responsible for; where it'll really help us out is when we get to magnetism, when we do magnetic flux.11Permittivity