There is a summary of the key characteristics of astronomical telescopes in a previous post, at https://physbang.com/2026/03/15/a-level-guide-to-astronomical-telescopes/. This article builds on that general overview by explaining a specific skill; how to draw a ray diagram for a refracting telescope in normal adjustment. First, what is "normal adjustment"? It is when the objective and eyepiece lenses … Continue reading Ray Diagram for a Telescope in Normal Adjustment
How to determine voltages inside a resistor network
Resistor networks sometimes look scary but they can be solved by taking things one step at a time and applying basic circuit rules. The rules concerned are the calculations for combining series and parallel resistors, together with Kirchoff’s two laws for circuits. To combine resistors, we add their values if they are arranged in series … Continue reading How to determine voltages inside a resistor network
Revision tips for Paper 3A
It’s a fool’s game to try to predict what will be in an examination paper but… looking back over past years, there are three practicals that have been used very little in Paper 3A and one of those hasn’t appeared since 2020. So, in my opinion, there is a good chance that this year’s paper … Continue reading Revision tips for Paper 3A
How to read a micrometer
Being able to take measurements using common items of instrumentation is an expected skill for A-Level Physics and can be tested in examinations using diagrams or photographs. This post is the first in a short series that will look at measurement skills, starting with a piece of equipment that often causes difficulties; the micrometer. To … Continue reading How to read a micrometer
Hypothesis and Analysis
When carrying out a practical investigation it is always helpful to know what sorts of results are expected. In other words, before starting an experiment it is a good idea to consider what theory tells us should be the outcome. The predicted findings form the basis of an hypothesis, which is developed by considering an … Continue reading Hypothesis and Analysis
Electron deflection tube
It is common to think of the electron deflection tube as a device that demonstrates the behaviour of electrons within an electric field but in fact there are two electric fields at work. The first field accelerates electrons that are released by a heated coil then the second field deflects those electrons as they travel … Continue reading Electron deflection tube
Electric Field & Electric Potential
It is tempting to regard the equations for electric fields and electric potentials as being separate things but they are so closely related that they are best viewed as different sides of the same coin. This is because electric field strength is the same as potential gradient. Or to put it another way, the electric … Continue reading Electric Field & Electric Potential
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