PhysicsMadrid 2026Question 1
Electric field between two plates
From potential to field, to acceleration and to speed: why it is solved this way
9 chapters · 7 minWatch the lesson →
Science · Mathematics · Technology
Don't memorise the solution. Understand why it's solved that way.
Exam problems explained in animated, narrated lessons. Always with the why: which method to choose, where each equation comes from and how to check the result.
Free and with no sign-up. 31 lessons, also available in Spanish.
What makes it different
The result matters least. What earns marks is knowing why.
The why is explained
Each chapter answers a question: why this method and not another, what principle lies behind it, what would happen with a different choice. Equations are derived, not recited.
Animation and voice together
The figure is built while two voices talk it through: Lucy asks what a student would ask and Dan answers. With subtitles, in chapters, and you can jump to any point.
Real exam questions
The problems come from real pre-university exams (the Spanish university entrance exam, PAU), translated into English and quoted with their source, year, session and question number.
How a lesson works
A few minutes per problem, in chapters of under a minute.
- Read before you calculateWhat the question or the graph says, and what can be anticipated without doing any sums.
- One chapter per part or per ideaWith the key ideas and their formulas appearing alongside as they are mentioned.
- Another route, when there is oneIt is solved by a second method, checked to give the same answer, and you are told when each one is the better choice.
- The answers and how to check themUnits, order of magnitude, and the limits of the model stated frankly.
And if you want all the detail
Every chapter has a «Full working» panel with the algebra step by step, the common mistakes and what makes an answer solid. The voice gives only the essential reasoning; the rest is written down for you to go over at your own pace.
It works on a phone, in light and dark mode, and you can change the speed of the voice.
Available lessons
All complete, free and with no sign-up.
ChemistryMadrid 2026Question 1
Corrosion of copper in nitric acid
Half-equation balancing, cell potential and precipitation: why each step is done this way
10 chapters · 9 minWatch the lesson →
MathematicsMadrid 2026Question 1
Rank with a parameter and a matrix equation
Matrices: why the determinant decides the rank, why a minor is needed, and why we multiply by the inverse on the left
10 chapters · 8 minWatch the lesson →
Mathematics for Social SciencesMadrid 2026Question 3.2
Linear programming: feasible region and minimum value
From each inequality to a half-plane, from half-planes to vertices, and why the optimum sits at a corner
10 chapters · 9 minWatch the lesson →
Technology and EngineeringMadrid 2026Question 2.2
Tensile test of an aluminium alloy
Yield strength, elongation at break, Hooke’s law and minimum diameter: which length and which units to use in each part, and why
10 chapters · 9 minWatch the lesson →
Technical DrawingMadrid 2026Question 1.1
Inverse arc under an inversion
Where the centre of inversion is, what its power is, and why each construction line is the way it is
9 chapters · 9 minWatch the lesson →
Quality
Every lesson is checked before it is published.
An explanation is only useful if it is correct. This is what is done with all of them.
A single source for every figure
All the numbers in a lesson come from one calculation. The voice, the formulas and the drawing cannot say different things.
Two routes that must agree
Each problem is solved by two methods and the results have to match.
A second, independent solution
The problem is solved again separately and the results are compared with those of the lesson.
Reviewed by a person
Before it is published, every lesson is reviewed by someone trained in the subject.
Who is behind it
Juan Carlos del Río
Telecommunications engineerPhysics graduateMathematics graduate
The lessons are prepared and reviewed by someone trained in engineering, physics and mathematics. The approach is that of someone who had to understand these problems, not just pass them: first the why, then the sums.
Pricing
Published problems are free. You only pay for a new one.
If your problem is not here, you will be able to ask for it: you send the question and receive its lesson.
Every published problem
All the published lessons, complete.
Free no sign-up
A new problem · Pre-university (ages 16–18)
You ask for a problem that is not here and its lesson is prepared.
from €0.50 per problem, VAT included
| Standard | €0.50 |
|---|---|
| Priority 24 h | €1.00 |
| Priority 8 h | €1.50 |
A new problem · University
You ask for a problem that is not here and its lesson is prepared.
from €1.00 per problem, VAT included
| Standard | €1.00 |
|---|---|
| Priority 24 h | €2.00 |
| Priority 8 h | €3.00 |
Requests are not open yet and nothing is charged through the site. Write to me and I will let you know when they open.
Shall I tell you when there are new lessons?
Send me an email and I will let you know. You can also ask for the problem you find hardest: it helps decide which ones come first.