Electric and Magnetic Fields | Edexcel A-Level Physics (9PH0)

Electric and Magnetic Fields

187 questions
19 subtopics
Paper 1: Advanced Physics I
Paper 1 and Paper 3

Paper 1 content covering electric fields from Coulomb's law to equipotentials, capacitance and exponential discharge, magnetic flux density and the forces on currents and moving charges, electromagnetic induction, and alternating current..

It covers electric fields and electric field strength, field strength calculations and field diagrams, coulomb's law and the field of a point charge, inverse-square behaviour and combining fields, electric potential and field strength as a potential gradient, uniform fields between parallel plates, and the potential near a point charge, equipotentials, field diagrams and work done, capacitance and the energy stored in a capacitor, capacitor charge and energy calculations, charging and discharging graphs and the time constant, the exponential decay equations and logarithmic graphs, investigating capacitor discharge and time-constant calculations, magnetic flux density, flux and flux linkage, forces on currents and moving charges, the conditions for inducing an e.m.f., faraday's law and Lenz's law, flux linkage graphs and induced e.m.f. calculations, alternating current, peak and r.m.s. values and oscilloscope traces and alternating current calculations.

Sample questions from Electric and Magnetic Fields

Answer each one closed book first, then open the answer.

Electric fields and electric field strength

How is electric field strength defined?

Show the answer
It is the force per unit positive charge acting on a small charge placed at that point in the field.
Coulomb's law and the field of a point charge

What is the value of the combination 1/(4πε₀)?

Show the answer
It is approximately 8.99 × 10⁹ N m² C⁻².
Electric potential and field strength as a potential gradient

Why does a minus sign appear in the relation between field strength and potential gradient?

Show the answer
Because the field acts in the direction in which potential decreases.
Equipotentials, field diagrams and work done

What do the equipotentials in the uniform field between two parallel plates look like?

Show the answer
They are straight lines parallel to the plates and equally spaced for equal steps in potential.
Capacitor charge and energy calculations

A 100 μF capacitor holds a charge of 6.0 mC. How much energy is stored?

Show the answer
W = Q²/(2C) = (6.0 × 10⁻³)² ÷ (2 × 100 × 10⁻⁶) = 0.18 J.
The exponential decay equations and logarithmic graphs

Which graph would you plot to obtain a straight line from discharge data, and what would its gradient be?

Show the answer
A graph of ln V against t gives a straight line of gradient −1/RC with intercept ln V₀.
Magnetic flux density, flux and flux linkage

What is the unit of magnetic flux?

Show the answer
The weber, Wb, where 1 Wb = 1 T m².
The conditions for inducing an e.m.f.

Why is no e.m.f. induced while a magnet is held stationary inside a coil?

Show the answer
Because the flux linkage is constant, so its rate of change is zero.

The 19 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Electric fields and electric field strength	Recall questions on what a field is, the definition E = F/Q and its unit, why N C⁻¹ and V m⁻¹ are the same, and why the test charge must be small.	10
Field strength calculations and field diagrams	Recall questions on finding force from field strength, whether the field depends on the charge placed in it, uniform fields, and how strength is shown by field-line spacing.	10
Coulomb's law and the field of a point charge	Recall questions on Coulomb's law, ε₀ and 1/(4πε₀), how the sign shows attraction or repulsion, and the radial field of a point charge.	10
Inverse-square behaviour and combining fields	Recall questions on how force and field strength change with separation, the log-log test for an inverse-square law, and finding a resultant field from two charges.	12
Electric potential and field strength as a potential gradient	Recall questions on the definition and unit of potential, field strength as minus the potential gradient, and reading each from the other's graph.	9
Uniform fields between parallel plates, and the potential near a point charge	Recall questions on E = V/d, the field between charged plates and where it stops being uniform, and the potential a distance r from a point charge.	8
Equipotentials, field diagrams and work done	Recall questions on what an equipotential is, the angle it makes with field lines, why field lines never cross, and the work done moving a charge through a potential difference.	9
Capacitance and the energy stored in a capacitor	Recall questions on the definition of capacitance and the farad, why Q/V is constant, and the three expressions for the energy stored.	11
Capacitor charge and energy calculations	Recall questions on finding charge and energy for a given capacitor and potential difference, the effect of doubling the potential difference, and why the supply delivers more than is stored.	9
Charging and discharging graphs and the time constant	Recall questions on the shapes of the charge, current and potential difference graphs, why the charging current falls, and the meaning of the time constant.	9
The exponential decay equations and logarithmic graphs	Recall questions on the decay equations for charge, current and potential difference, and the linear form obtained by taking natural logarithms.	8
Investigating capacitor discharge and time-constant calculations	Recall questions on recording a discharge, why a large resistance and a high-resistance voltmeter are needed, and finding the time constant and half-time.	11
Magnetic flux density, flux and flux linkage	Recall questions on flux density and its unit, magnetic flux and flux linkage, and how field strength is shown on a field-line diagram.	9
Forces on currents and moving charges	Recall questions on F = BIl sinθ and F = BQv, Fleming's left-hand rule, why a magnetic field does no work, and why a charge entering at right angles follows a circle.	14
The conditions for inducing an e.m.f.	Recall questions on what must change for an e.m.f. to be induced, the three factors that set its size, why a steady current induces nothing, and the effect of an iron core.	8
Faraday's law and Lenz's law	Recall questions on the two laws and the single equation expressing both, what the minus sign means, how Lenz's law follows from energy conservation, and the magnet-in-a-copper-tube effect.	8
Flux linkage graphs and induced e.m.f. calculations	Recall questions on the gradient of a flux linkage against time graph, why its unit is the volt, electromagnetic braking, and calculating an induced e.m.f.	8
Alternating current, peak and r.m.s. values	Recall questions on frequency and period of an alternating supply, peak and peak-to-peak values, the r.m.s. definition, and why mains supplies are quoted as r.m.s.	10
Oscilloscope traces and alternating current calculations	Recall questions on reading period and peak potential difference from a trace, converting between peak and r.m.s., and the mean power dissipated in a resistor.	14

Electric and Magnetic Fields is 187 of the 1,616 questions in the guide.Get the guide, £8

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.