Page 105 - Physics Form 5 KSSM_Neat

Electric Field Strength CHAPTER 3
Assume that a positive test charge, q is placed in an electric field. The test charge will experience
an electric force. This force can either be a repulsive or an attractive force depending on the type Electricity
of a charged particle. Figure 3.4 shows an electric force acting on a positive test charge.

KEMENTERIAN PENDIDIKAN MALAYSIA
Repulsive force Attractive force
+ + F – + q
q F

Figure 3.4 Electric force acting on a positive test charge in an electric field

The electric field strength, E at a given point in an Info GALLERY
electric field is defined as the electric force acting on The electric field lines follow
a unit positive charge placed at the point. the direction of the force on a

E = F positive test charge that is placed
q in the electric field.
where E = electric field strength
F = electric force
Let’s Recall
q = quantity of electric charge Let’s Recall
–1
The S.I. unit for E is newton per coulomb (N C ) The S.I. unit for
charge is coulomb (C).

Figure 3.5 shows a uniform electric field between two oppositely charged parallel plates.
A uniform electric field is represented by a set of parallel electric field lines.

+ + + + + + +
Electric
field lines d V +
–

– – – – – – –

Figure 3.5 A uniform electric field between two oppositely charged parallel plates

The electric field strength, E produced by two parallel charged
plates is
E = V
d
where E = electric field strength Info
–1
–1
V = potential difference between two parallel plates V m is equivalent to N C .
d = distance between two parallel plates
The S.I. unit for E in this formula is volt per metre (V m )
–1

LS 3.1.2 95