4.2.3Electricity and Magnetism
Electric Fields — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 10 parts Lesson 17 of 65 1 quiz
Lesson summary
4.2.3 Electric Fields — IGCSE PHYSICS notes: Define an electric field, state its direction and sketch field lines for point charges, spheres and parallel plates.Electric field = a region of space in which an electric charge experiences a force.Direction — the direction of the fie…
- No crossing
- Conductors
- Positive charge
- Negative charge
- Demonstration
- Uniform field
Part 1 of 8What is an electric field? (Extended)
Electric field
Electric field a region of space in which an electric charge experiences a force.
Direction
- Direction the direction of the field at a point is the direction of the force on a positive charge there.
- A negative charge in the same field feels a force in the opposite direction.
Vector
- Vector an electric field has both magnitude (strength) and direction.
Source
- Source charged objects create electric fields around themselves, as magnets create magnetic fields.
Part 2 of 8Rules for field lines
Direction
- Direction lines point from the positive charge to the negative charge.
Strength
- Strength where lines are closer together the field is stronger.
No crossing
- No crossing lines never cross, because the field has only one direction at a point.
Conductors
- Conductors lines meet the surface of a conductor at right angles.
Part 3 of 8Field around a point charge
Positive charge
- Positive charge the lines are straight and radially outward.
Negative charge
- Negative charge the lines are straight and radially inward.
Distance
- Distance the lines spread out with distance, so the field weakens.
Part 4 of 8Field around a charged conducting sphere
Pattern
- Pattern it is similar to that of a point charge.
Reason
- Reason the like charges repel and spread evenly over the conducting surface.
Lines
- Lines they are perpendicular to the surface.
Demonstration
- Demonstration a Van de Graaff generator can show the pattern.
Part 5 of 8Field between parallel plates
Field between parallel plates
Uniform field
- Uniform field between two oppositely charged parallel plates the lines are straight, parallel and equally spaced.
Direction
- Direction the lines run from the positive plate to the negative plate.
Edges
- Edges the lines bulge outwards near the edges.
Charged particle
- Charged particle a positive particle accelerates towards the negative plate and a negative particle towards the positive plate.
Part 6 of 8Two point charges
Opposite charges
- Opposite charges the lines curve from the positive charge to the negative charge.
Like charges
- Like charges the lines bend away from each other, and there is a neutral point halfway between equal charges where the field is zero.
Part 7 of 8Charged particles in fields
Charged particles in fields
Force
- Force bigger charge or stronger field gives a bigger force, in the direction of the field for positive charge and against it for negative.
Deflection
- Deflection a charged particle entering at right angles to a uniform field follows a curved path towards the oppositely charged plate.
- A more massive particle is deflected less because the same force gives a smaller acceleration.
Neutral particles
- Neutral particles an uncharged object, such as a neutron, passes straight through.
Uses
- Uses paint sprayers, oscilloscopes and ink-jet printers use fields to steer charged particles.
Part 8 of 8More from the specification
More from the specification
Nature of Electric Fields
- An electric field is a region where an electric charge experiences a non-contact force;
- for example, rubbing a polythene rod generates static charge that attracts neutral paper bits.
Potential Difference
- The electrical energy transferred per unit charge passing between two points in a circuit (V = W / Q), measured in volts using a parallel-connected voltmeter.
Electric Current
- The continuous flow of charge carriers around a conductive path, quantified as rate of charge movement (I = Q / t) and measured in amperes with a series ammeter.What the symbols mean: Q = charge (C) · I = current (A) · t = time (s)
Resistance and Power Dissipation
- The opposition to current flow in circuit components produces electrical power dissipation as thermal energy, governed by P = VI = I2 R.
Alternating current
- Current that continually reverses direction.
Electromotive force
- Energy transferred from other forms to electrical energy per unit charge.
Gold-leaf electroscope
- A device in which a charged gold leaf falls when photoelectrons discharge the plate.
Mains supply
- Domestic a.c. supply, rated 230 V rms at 50 Hz in the UK.
Electrical power
- Rate of energy transfer, P = I V.What the symbols mean: P = power (W) · I = current (A) · V = potential difference (V)
Current
- Flow of electrons in a circuit.
Resistance
- Opposition to current, R = V / I, in ohms (Ω).
Electroscope
- Instrument with a metal cap, stem and gold leaf used to detect charge.
Terminal
- Connection point of a cell, labelled + or −.
Insulator
- Material that does not allow current to flow.
Component
- Part of a vector along one axis.
Potential difference
- Work done by a unit charge passing through a component.
Energy transferred
- W = V Q, in joules.What the symbols mean: E or W = energy transferred (J) · Q = charge (C) · V = potential difference (V) · I = current (A) · t = time (s)
Key terms
| Term | Meaning |
|---|---|
| Electric field | Region of space in which an electric charge experiences a force. |
| Field line | Line showing the direction of the force on a positive charge. |
| Uniform field | Field of the same strength and direction everywhere, shown by parallel equally spaced lines. |
| Point charge | Charge concentrated at a single point. |
| Van de Graaff generator | Machine that builds up a large charge on a metal sphere. |
Avoid these mistakes
1
Drawing field lines that cross — lines can never cross.
2
Putting the arrows the wrong way — lines go from positive to negative.
3
Saying a negative charge moves along the field direction — it moves opposite to the field arrows.
4
Drawing uneven spacing between plates — a uniform field has parallel, equally spaced lines.
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