Presentation on theme: "Definition of a Field Field Lines Electric Fields Superposition"— Presentation transcript:
1 Definition of a FieldField LinesElectric FieldsSuperpositionRelationship to Electric ForceField as a Physical Property
2 Field Examples of Fields: The influence of some agent, as electricity or gravitation, considered as existing at all points in space and defined by the force it would exert on an object placed at any point in space.Fields are things which change their value depending on what point in space or time you are measuring them.They may depend on direction (vector fields) or they may not (scalar fields).Examples of Fields:Temperature Profile (scalar)Wind Velocity Profile (vector)
3 DefinitionsMagnitude: The amount of a quantity represented by a vector or scalar.Direction: The angle of a vector measured from the positive x-axis going counterclockwise.Scalar: A physical quantity that has no dependence on direction.Vector: A physical quantity that depends on direction.Field: A set of an infinite number of related vectors or scalars found at every point in space and time.Units: A standard quantity used to determine the magnitude of a vector or value of a scalar.
4 Example of a Vector Change Wind Speed Wind Velocity is a vector Its magnitude is changed when it increases and decreases its speed.Its direction is changed when it changes the compass angle toward which it blows.Change WindDirectionGraphicalRepresentationNReal LifeMathematicalRepresentationMagnitude6181224weDirectionSouthwestSoutheastNortheastNorthwestUnitsmphs
5 Example of a Scalar Temperature is a scalar Its magnitude is changed when it heat is added or taken away.It has no direction.ChangeTemperatureReal LifeGraphicalRepresentationDegrees CMathematicalRepresentationMagnitude502575100DirectionnoneUnitsdegrees F
6 Example of a Vector Field Wind Velocity is a function of position.This position is given by the latitude and longitude of the vector’s tail.GraphicalRepresentationNMathematicalRepresentationPositionMagnitude1110201214411556Latitude40°28°30°41°38°47°32°47°40°29°NDirection*44°43°2°45°225°315°0°2°85°85°Longitude95°81°123°118°100°106°91°83°86°73°WUnitsmph* Angles for direction are taken counterclockwise from East.
7 Example of a Scalar Field 657482Example of a Scalar Field5862Temperature is a function of position.This position is given by the latitude and longitude of the point where the temperature is taken.7548518287GraphicalRepresentationNMathematicalRepresentationPositionMagnitude74658287628251487558Latitude47°30°29°41°47°32°40°28°38°40°NDirectionnoneLongitude86°106°123°118°100°91°81°73°83°95°WUnitsdegrees F
8 Wind velocity can be represented by placing arrows at many locations. Each arrow represents the value of the velocity at the location of the tail of the arrow.The direction of the arrow gives the direction of the wind velocity.The length of the arrow gives the magnitude of the wind velocity.
9 The wind velocity can also be represented by lines. The lines do NOT connect the arrows!The lines are closer together where the magnitude of the wind velocity is greater.The direction of the wind velocity at a point on any line is tangent to the line.
10 Electric Fields q1 q0 Consider two positive charges, q0 and q1. The force from q1 on q0 is given by Coulomb’s Law.This last equation is true regardless of the value of q0.q1q0
11 Electric FieldsWe could now divide by q0 and this is what we call the electric field at the point where q0 used to be.Notice that it no longer depends on the value of q0. It depends only on a position.q1q0
12 Electric FieldsFor a point charge, the electric field changes only with its distance from the charge.It gets smaller as you move away from the charge.q1
13 Electric FieldsIf we draw the filed lines, we can see that they get less dense with distanceThe number of lines is proportional to the amount of charge.q1
14 Electric Fields are fields which add as vectors Electric fields add the same way electric forces do, as vectors.The electric field is different at different locations.The magnitude of the electric field for a point charge iswhere 0 tells us the position at which the measurement is being taken.
15 Finding Electric Force To find the force exerted by q1 on another charge q0, use the equationwhere E1,0 is the electric field at the point where the charge is found.
16 Electric Field is a physical property of a particle with charge Electric field is something we can measure independent of other charges.For a given particle, the electric field around it never changes unless we physically change the particle.Electric fields have their own energy and momentum.We can talk about the electric field even when the charge that causes the field is unknown.
17 Definition of a FieldField LinesElectric FieldsSuperpositionRelationship to Electric ForceField as a Physical Property