Electric fields Flashcards
What is a force field?
A region in which a body experiences a non-contact force.
How do force fields arise?
From the interaction of mass, of static charge, and between moving charges.
What are the similarities between gravitational and electrostatic forces?
- Both electric and gravitational forces are non-contact & have infinte range.
- Inverse-square law.
What are the differences between gravitational and electrostatic forces?
- Gravitational forces are always attractive, electric forces can be attractive or repulsive.
- Electric force is stronger than gravitational force.
- It is possible to shield an electric force, but gravitational force acts on all objects.
- Electric force only acts on charged objects, but gravitational force acts on all objects.
How is electric field strength defined?
Force per unit charge: E = F/Q
What direction is an electric field said to have?
Direction of the force on a positive charge.
How to calculate magnitude of unifrom field between two plates?
Word done to move a charge in the field towards positive:
word done = Fd = EQd
this is equal to the potential energy gained by the charge moving through a pd V:
EQd = VQ
⇒ E = V/d
How to work out:
- time taken
- vertical acceleration
- vertical displacement
of a charged particle moving in an electric field
- No acceleration horizontally so use v=d/t
- E = F/Q ⇒ F = EQ = VQ/d. a = F/m = VQ/md
- suvat with above values
What is the expression for magnitude of E in a radial field?
E = Q/4πE0r2
What is absolute electric potential?
Work done per unit charge in moving a unit (Q=1) positive charge from ∞ to a distance r away from another charge +Q. It is given by:
V=Q/4πE0r
How is V related to E?
E = _delta V/_delta r
What are equipotential surfaces?
Equipotential surfaces are surfaces which lie at right angles to the field lines. This means that the absolute potential at any point along the surface is the same, so there is no work done by the electric field by moving a charge along an equipotential surface.
