Electric FieldLesson 3

Continous assessment

1.Define an electric field.It is the space around a charge where another charge feels a force.2.How do you represent an electric field? By electric field lines. The direction of the arrows shows the direction of the field.The spacing between the lines tells us about the strength of the field.

3.Define electric field strength (E) .• It is the force felt by 1coulomb of positive

charge.

• Electric field strength( E ) = Force F)/Charge(Q) E=F/Q or F= QE

• Unit is Newton/Coulomb (N/C) or Volt/metre (V/m)

• E is a vector

Force experienced by a charge in an electric fieldConsider a uniform field of strength E.

If you place a charge +Q in the field ,it will experience a force F=QE in the direction of the field.

If you place a charge -Q in the field ,it will experience a force F= - QE in the opposite direction of the field.

+Q

E

F=QE

--QF= -QE

Electric field strength of a uniform electric fieldElectric Field strength(E)=Potential difference across the plates(V)/seperation between the plates E=V/d ; unit = V/m

+ + + +

- - - -

d

V

E

Electric field strength of radial Electric field

A point charge +Q produces a radial field. A small positive test charge is placed in the field. Using Coulomb’s law the force on the test charge +q is given by F=k Qq/r²El. Field strength is force per unit chargeE=F/q = k Qq/r²q E = k Q/r²

Q+q

Fr

Continous assessmentPage257

Electric potential

• Electric potential at a point is the electric potential energy of a unit positive charge placed at that point

• Unit : Joule/ coulomb or volt