The Physics
Hypertextbook
Opus in profectus

# Electric Field

## Summary

• Field
• A field is…
• a physical quantity that has a value (or set of values) at every point in space and time
• a mathematical function that returns a value (or set of values) for every point in space and time
• a way to deal with philosophical arguments against action at a distance
• Fields can be…
• scalar fields associated with quantities such as…
• temperature
• pressure
• density
• electric charge
• vector fields associated with…
• the flow of fluids (the velocity field) such as…
• wind
• ocean currents
• solar wind
• non-contact forces (force fields) such as…
• gravitational field
• electric field
• magnetic field
• tensor fields associated with…
• continuum mechanics quantities, namely the…
• stress tensor
• general relativity quantities such as the…
• metric tensor
• stress-energy tensor
• Ricci curvature tensor
• Electric field
• Magnitude  E = FE q
Where…  E = magnitude of electric field (electric field strength) Fg = electric force on test charge q = charge of test charge
• The electric field has two frequently used, equivalent SI units…
• the newton per coulomb and
• the volt per meter.
 ⎡⎢⎣ N = V ⎤⎥⎦ C m
• Direction
• Electricity is described by a vector field.
• The direction of the electric field at any point in space is the direction of the net electric force on a "small" positive test charge.
• Use vector addition to find the net electric field when more than one charged object is present.
• Diagrams
• The electric field around a spherically symmetric charge is radial and…
• diverges from positive charge
• converges on negative charge
• Field lines never intersect.
• Electric field strength is proportional to line density.