CCEA A Level Physics
CCEA A Level Physics 5.3 Electric Fields Exam Questions
Free CCEA A Level Physics revision for 5.3 Electric Fields: what you need to know, common mistakes and exam-style questions with answers. Covers electric field strength, coulomb's law, point charge fields, uniform fields between plates, E = V/d and comparison with gravitational fields.
Practise 5.3 Electric Fields with past papers
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About CCEA A Level Physics 5.3 Electric Fields
Electric fields is the second field topic in Unit A2 2: Fields, Capacitors and Particle Physics. You need to define electric field strength as force per unit positive charge, use Coulomb's law for the force between point charges and calculate the field around a point charge. Between parallel plates the field is uniform and E = V/d. You must also compare electric and gravitational fields, noting their similarities as inverse square laws and the key differences. This content leads straight into capacitors and the deflection of charged particles. Examiners commonly ask for field line diagrams, Coulomb's law calculations with microcoulombs and a structured comparison with gravity.
What you need to know
- Electric field strength E = F/q, the force per unit positive charge, unit N C-1 (equivalent to V m-1). The direction is the direction of the force on a positive test charge.
- Coulomb's law F = Qq / (4πε0 r^2), where ε0 = 8.85 x 10^-12 F m-1, so 1/(4πε0) is about 8.99 x 10^9 N m^2 C-2. Like charges repel; unlike charges attract.
- Point charge field E = Q / (4πε0 r^2), a radial field following an inverse square law. Field lines point away from a positive charge and towards a negative one.
- Uniform fields Between parallel plates the field lines are parallel and equally spaced, and E = V/d, where V is the p.d. and d is the plate separation.
- Comparison with gravity Both are inverse square fields with similar equations. Gravity acts on mass and is always attractive; electric forces act on charge and can attract or repel. Electric forces between particles are vastly stronger than gravitational ones.
Common mistakes in 5.3 Electric Fields
- Forgetting to square r in Coulomb's law, or using the diameter of a sphere instead of the distance between centres.
- Not converting microcoulombs (μC) or nanocoulombs (nC) to coulombs.
- Drawing field lines between plates that are curved in the middle; they should be parallel and evenly spaced, with slight curving only at the edges.
- Saying gravitational and electric fields are the same type of field; they act on different properties and only gravity is purely attractive.
- Defining field strength as force per unit charge without saying positive charge.
Try three 5.3 Electric Fields exam-style questions
1. Two point charges of +2.0 μC and -3.0 μC are 0.10 m apart. Calculate the force between them. (3 marks)
Show the mark scheme answer
F = 8.99 x 10^9 x 2.0 x 10^-6 x 3.0 x 10^-6 / (0.10)^2; = 5.4 N; attractive.
2. Two parallel plates 2.0 cm apart have a p.d. of 500 V across them. Calculate the field strength and the force on an electron between them. (3 marks)
Show the mark scheme answer
E = V/d = 500/0.020 = 2.5 x 10^4 V m-1; F = eE = 1.6 x 10^-19 x 2.5 x 10^4; = 4.0 x 10^-15 N.
3. State one similarity and two differences between gravitational and electric fields. (3 marks)
Show the mark scheme answer
Similarity: both follow an inverse square law for point sources (radial fields); difference: gravity acts on mass, electric fields act on charge; gravity is always attractive whereas electric forces can be attractive or repulsive.
5.3 Electric Fields FAQs
What does CCEA A Level Physics 5.3 Electric Fields cover?
Electric field strength, Coulomb's law, the field of a point charge, uniform fields between parallel plates with E = V/d, and the comparison between electric and gravitational fields.
Which unit is 5.3 examined in?
It is in Unit A2 2: Fields, Capacitors and Particle Physics.
What equations do I need for electric fields?
E = F/q, F = Qq/(4πε0 r^2), E = Q/(4πε0 r^2) and E = V/d.
