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Advanced Higher Physics
Electrical Field
Electrical Field Strength 1
(measured in NC-1)

E = F/q

Defined as ‘the force F acting per unit positive
charge q placed at a point in the field’

E
Q
40 r
2
Electrical Field Strength 2
Examples –
1. Find the electric field strength, E, at a
distance, r, of 1.5 m from a charge, Q, of
2.5 nC.
E
Q
40 r 2
9
2
.
5

10
 8.99 109 
1.52
 9.99 NC 1
Electrical Field Strength 3
2. The electric field strength, E, is 3.8 NC-1 at a
distance, r, of 2.0 m.
What is the size of the charge?
Q  40 r E
2
 8.85 10
12
 2.0  3.8
 1.34 10 10 C
2
Electric Field Diagrams 1

We can draw the electric
field in the region around a
charge.
 For point charges the fields
are radial.
 Arrows show the direction
of force experience by a
positive (+) charge.
 Spacing of arrows relates
to field strength.
Electric Field Problems

Scholar Examples

Scholar Demo
Electric Field Diagrams 2

Fields between like charges

Fields between like charges
Electric Field Diagrams 3

Fields around charged plates
Electric Field Diagrams 4

Field between oppositely charged plates
This is a parallel or
uniform field.
 Field strength is equal
at all points inside field
