Electric field lesson -3

2. 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. 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

4. Force experienced by a charge in an electric field
Consider a uniform field of strength E.
F= -QE --Q
+Q
E
F=QE
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.

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

6. Electric field strength of radial Electric field
Q
+q
r F
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/r²
El. Field strength is force per unit charge
E=F/q = k Qq/r²q E = k Q/r²

7. Continous assessment
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8. 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