An electric force of 4.5 x N is measured between two particles. One particle has a charge of 2.0 x C & the other has a charge of 3.0 x C. Calculate the distance between them.

Chapter 21 Electric Fields

Electric force like gravitational force is inversely proportioned to the square of the distance between the two points of concern

Electric Field (E) A vector quantity that relates the force exerted on a charge to the amount of the charge

Electric Field (E) E = F on q q

Electric Field (E) F on q = qE

Calculate the electric field strength when a 25 N force is exerted on a charge of x C

Typical Field Strengths FieldValue (N/C) TV tube1 x 10 5 Spark r3 x 10 6 H orbital5 x 10 11

Electric Field Lines Lines representing the force vectors in an electric field

Electric Field Lines +

-

+ -

Always point from positive to negative

Electric Field Lines Do not exist, but provide a model of a field

The electric field between two parallel plates is uniform

+-

Electric Potential The electric potential difference of charges measured in volts

Electric Potential As with heat, we can only measure potential difference (  V)

Electric Potential Difference (  V) The change in potential energy per unit charge

Electric Potential Difference (  V) The work done moving a charge thru a field charge

Electric Potential Difference (  V) Measured in J/C J/C = volt (V)

Electric Potential Difference (  V) W on q q  V =

Electric Potential Difference (  V)  U = W

Electric Potential Difference (  V) UqqUqq  V =

Electric Potential Difference (  V) W on q q  V =

Electric Potential Difference (  V) W = Fd

Electric Potential Difference (  V) Fd on q q  V =

Electric Potential Difference (  V) FqFq  V = x d

Electric Potential Difference (  V) FqFq E =

Electric Potential Difference (  V)  V = E d

Basic Equations V = Ed W = qV F = qE

Equipotential When the electric potential difference is 0

Equipotential Charge rearranges itself to reach equipotential

Equipotential When two spheres have the same charge, the larger one has lower electric potential

Equipotential When two spheres have the same electric potential, the larger one has the greater charge

Equipotential When a charged object comes in contact with a neutral one, the charge is equally distributed

Equipotential Because of the size of Earth, when objects touch Earth, their charge is passed to the Earth

Grounding When a charged object touches Earth, all its charge flows to Earth creating equipotential

Electric Fields All charges are on the outside of a conductor

Electric Fields In pointed object, the field strength is greatest at the point

Capacitor A device designed to store a charge

Capacitance The ratio of charge to electric potential difference

Capacitance (C) C = q  V

Farad (F) Unit for capacitance measured in coulombs per volt: F = C/V

Basic Equations V = Ed W = qV F = qE q = CV

A charge of 1.6 x C is stored to create a capacitance of 4.0 x F acting over 2.0  m. Calculate: V, E, F, & W

A charge of 1.5 x C is stored to create a capacitance of 4.0 x F acting over 2.0 mm. Calculate: V, E, F, & W

A charge of 3.2 x C is stored to create a capacitance of 8.0 mF acting over 4.0  m. Calculate: V, E, F, & W

Charge =1.6 x C Force = 3.2 x N Distance = 64 nm. Calculate: V, E, C, & W

Calculate: 3.2 x x 1.5 x  8.0 x  7.5 x x 4.0 x =

Calculate: 3.2 x x 1.5 x  8.0 x  7.5 x x 2.0 x =