Ch – 26 Electric Field

Electric Field Model

• One or more charges (source charges) alter the space around them by creating an electric field, E.

• A separate charge (test charge or probe) experiences a force F, exerted by the field.

• F = qE

Electric Field of a Point Charge

The unit vector points outward from the source charge

If q is negative the vector is reversed and points inward, toward the source charge

Electric Field Simulation

Electric field of a dipole

• Two equal and opposite charges small distance apart

• Zero net charge but it causes an E field

• Dipole moment:

p = qs, pointing from negative to positive

Electric Field of a Dipole

E Field for an Infinite line of Charge

Picturing the Electric Field

Electric Field of a Dipole

E Field for an Infinite line of Charge

Electric Field of a Ring of Charge

(Ering)z = [1/(4πε0)] [zQ/(z2+R2)3/2]

Electric Field of Charged Disk

Limit as R ∞

Note that this value of E does not depend on the distance from the charged plane (z), only on the surface charge density

Electric field strength of an infinitely charged plane is independent of

distance from the charge

Parallel Plate Capacitor

A parallel plate capacitor provides a uniform electric field.

Motion of a charged particle in a uniform electric field

• a = F/m = qE/m = constant

• direction of a parallel to E

• charged particle will accelerate/decelerate in the direction of E

• projectile motion, if v0 is not parallel to E

Motion in a Nonuniform Field

• circular motion of a charged particle around a point charge, charged sphere or wire

|q|E = mv2/r

Simulation labSimulation lab

Superposition problem

Earth’s internal structure

Figure 1.13

Plate tectonics: the new paradigm

Plate boundaries • Types of plate boundaries

• Divergent plate boundaries (constructive margins)

• Two plates move apart• Mantle material upwells to create new

seafloor • Ocean ridges and seafloor spreading

• Oceanic ridges develop along well-developed boundaries

• Along ridges, seafloor spreading creates new seafloor

Figure 15.10a

Figure 15.12

Plate tectonics: the new paradigm

Plate boundaries • Types of plate boundaries

• Convergent plate boundaries (destructive margins)

• Oceanic-continental convergence • Denser oceanic slab sinks into the

asthenosphere • Pockets of magma develop and rise • Continental volcanic arcs form• Examples include the Andes,

Cascades, and the Sierra Nevadan system

Figure 15.14a

Plate tectonics: the new paradigm

Plate boundaries • Types of plate boundaries

• Convergent plate boundaries (destructive margins)

• Oceanic-oceanic convergence • Two oceanic slabs converge and one

descends beneath the other • Often forms volcanoes on the ocean

floor • Volcanic island arcs forms as

volcanoes emerge from the sea • Examples include the Aleutian,

Mariana, and Tonga islands

Figure 15.14b

Plate tectonics: the new paradigm

Plate boundaries • Types of plate boundaries

• Convergent plate boundaries (destructive margins)

• Continental-continental convergence • When subducting plates contain

continental material, two continents collide

• Can produce new mountain ranges such as the Himalayas

Figure 15.14c

Plate tectonics: the new paradigm

Plate boundaries • Types of plate boundaries

• Transform fault boundaries • Plates slide past one another

• No new crust is created or destroyed • Transform faults

• Most join two segments of a mid-ocean ridge

• Aid the movement of oceanic crustal material

Figure 15.16