Exam season is over so this seems like a good time to admit that physicists don’t know all the answers – and don’t even always agree on which of the available answers is best. The two biggest areas of disagreement are cosmology and quantum mechanics. For example; What do we mean by the “Big Bang”? … Continue reading Answers to some of physics’ biggest mysteries
Instrument resolution and experimental accuracy
Uncertainties in measurements arise from the equipment used and the method employed. As the final paper for this year’s A-level Physics examination is imminent, and tests knowledge of uncertainties, it is worth taking a moment to examine the causes of uncertainty in more detail. We will do this by thinking about two example measurements; one … Continue reading Instrument resolution and experimental accuracy
Know your calculator!
When answering examination questions, it is important that your excellent knowledge of physics isn’t undermined by your calculator behaving in an unexpected way. You MUST be able to trust the answer given. But the situation is potentially complicated, not only because calculators don’t all behave the same way but also because they may not even … Continue reading Know your calculator!
At what rate is the Universe expanding?
When Edwin Hubble first used data to determine whether “nebulae” were part of our own galaxy, he found they were in fact moving away from the Milky Way at a rate proportional to their observed distance. The most distant of these objects (now known to be galaxies) were receding at the greatest speed. This in … Continue reading At what rate is the Universe expanding?
Ray Diagram for a Telescope in Normal Adjustment
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
Red-Shift and the Age of the Universe
Stars can be characterised by their absorption lines, which reveal their temperature and composition. There is more detail about this in two recent posts about the HR diagram and stellar classification. A similar approach can also be used to characterise entire galaxies but in this case the aim is to determine how quickly they are … Continue reading Red-Shift and the Age of the Universe
The formation, life and death of stars
All stars are born through the same basic mechanism but their evolution depends on their size. In particular, all stars go through a hydrogen-fuel stage but the time spent fusing hydrogen is determined by the star's initial mass. The final fate of a star is also predicted by its mass; some stars will simply fade … Continue reading The formation, life and death of stars
Classification of Stars
The obvious way to classify stars is by their appearance; how bright they are and their colour. In both cases, we are referring to properties judged using the human eye from the location of planet Earth. Sadly, our eyes are not a good judge of colour (equal amounts of red and green light are perceived … Continue reading Classification of Stars
Electricity: models and theories
Physics can get complicated at times and when it does, we use models to simplify things. The models aren’t wrong: in fact they work remarkably well, but they aren’t complete. Electricity provides probably the best examples of this state of affairs. Models normally start at the level of “electrons as buckets carrying energy” and include … Continue reading Electricity: models and theories
A-level guide to astronomical telescopes
The first section of the Astrophysics module for AQA A-level Physics is all about telescopes. This post is a brief summary of that section’s key learning points. Telescopes aren’t used simply to make astronomical objects “bigger” or to get a “closer” view. It is true that nearby objects, such as our moon and other bodies … Continue reading A-level guide to astronomical telescopes
Mr Tarrant's physbang 'blog 