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
Radiation detectors
The first device that comes to mind as a radiation detector (for use in schools) is probably the Geiger-Mueller (GM) tube. Although GM tubes can be used to detect all three types of ionising nuclear radiation (alpha, beta and gamma) they are subject to some important limitations. These shortcomings will be discussed below, together with … Continue reading Radiation detectors
Does radiation make things radioactive?
The short answer is “no” but the devil is always in the detail. Firstly, “radiation” here applies specifically to ionising radiation; alpha particles, beta particles and gamma photons. In particular, we are excluding non-ionising nuclear radiation in the form of neutrons, which definitely can turn previously stable nuclei into radioactive materials. This effect is a … Continue reading Does radiation make things radioactive?
What are lumens? (part 2)
In the previous discussion about lumens (https://physbang.com/2025/12/30/what-are-lumens/) some numbers were quoted without any explanation. This post adds a bit more detail to those numbers. Firstly, the maximum theoretical output of a light source was stated to be 683 lumens-per-watt. Why that number? The answer is to be found in the definition of the candela, which … Continue reading What are lumens? (part 2)
What are lumens?
Modern light sources are rated in lumens or, more importantly, lumens per watt. The first figure expresses the brightness of the source whereas the second indicates its efficiency. But what, exactly, is a lumen? To answer that question it is useful to recall that the first man-made light sources relied on heat and were very … Continue reading What are lumens?
Electron Capture and Internal Conversion
Having looked at some of the finer details for beta decay in two previous posts (Q-Value and Metastable Nuclei) it seems fitting to round-off this short series with two phenomena that involve orbiting electrons rather than just nucleons. The first effect is electron capture. As its name suggests, this is when an orbiting electron is … Continue reading Electron Capture and Internal Conversion
Technetium-99m
At first glance the decay of molybdenum-99 to produce technetium-99 is a straightforward beta process. The total number of nucleons is unchanged but the number of protons increases by one with the emission of an electron and an electron-antineutrino. The half-life for this decay is 66 hours. In the nuclear decay equation above, technetium-99 is … Continue reading Technetium-99m
Beta Decay Q-value
At GCSE level, beta decay is said to be the emission of an electron (or positron, in beta-plus decay) when an unstable nucleus transforms into a more stable nucleus. The parent and daughter nuclei are different elements with the same nucleon number (sum of neutrons and protons) but their proton numbers vary by +1 for … Continue reading Beta Decay Q-value
Nobel Prize for Physics 2025
Strange things happen in the quantum world. It’s not just the events that are strange: the ways in which they happen are also weird. Take the nucleus, for example. Things were bad enough when Ernest Rutherford proposed that the atomic nucleus was very small, very dense and packed with positive charge. But things got even … Continue reading Nobel Prize for Physics 2025
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