# Electric field strength ```1 of 7
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AQA
3.4.3b Electric field strength: E is defined by E = F / Q; magnitude of
E in a radial field given by E = 1 / 4πε0 Q / r2; magnitude of E in a
uniform field given by E = V / d.
Edexcel Topic 4.4 – Electric and magnetic fields
83. Explain what is meant by an electric field and recognise and use
the expression electric field strength E = F / Q.
84. Draw and interpret diagrams using lines of force to describe
radial and uniform electric fields qualitatively.
85. Derive and use the force between two charges expression for
the electric field due to a point charge.
86. Recall that applying a potential difference to two parallel plates
produces a uniform electric field in the central region between them,
and recognise and use the expression E = V / d.
OCR
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5.1.1b Define electric field strength as force per unit positive charge.
5.1.1c Describe how electric field lines represent an electric field.
5.1.1e Apply E = Q/4πε0r2 for electric field strength of a point charge.
5.1.1f Select and use E = V / d for the magnitude of the uniform
electric field strength between charged parallel plates.
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Placing a charge in an electric field
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Electric field strength
Electric field strength is defined as the force experienced
per unit charge. The charge in the equation refers to the
charge of the particle in the field.
electric field strength = force / charge
E = F/Q
Example: What is the electric field strength around a
point charge if a 3.20 &times; 10-19 C charge experiences a
force of 7.30 &times; 10-15 N?
E = F/Q
E = (7.30 &times; 10-15 ) / (3.20 &times; 10-19 )
E = 2.28 &times; 104 N C-1
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Electric field strength: uniform fields
The electric field between two parallel plates (e.g. capacitor
plates) is uniform: a charge will experience the same force
wherever it is placed between the plates.
The electric field strength
depends on two factors:
the voltage between the
plates and the distance
between them.
electric field strength = voltage / distance
E = V/d
The units of E in this instance are volts per metre (V m-1).
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