Recent content by iantresman

  1. I

    I Largest sphere in the space between dense packed spheres

    I didn't know where to start, whether drawing a tetrahedron and 2D circles is relevant.
  2. I

    I Largest sphere in the space between dense packed spheres

    If I consider a tetrahedron of four densely packed spheres of unit radius, what it the radius of the largest sized sphere that can fit in the space in between?
  3. I

    B Electrical version of Faraday effect?

    Thanks for that. So the Kerr Effect induces birefringence in the direction of the field, and the Pockels Effect induces birefringence perpendicular the field. I wonder whether either effect is used in an astrophysics context? I note that there is "A novel technique for remote sensing of...
  4. I

    B Electrical version of Faraday effect?

    The Faraday effect is a magneto-optical phenomenon caused by the interaction between light and a magnetic field. Is there a corresponding electrical-optical phenomenon, caused by the interaction between light and an electric field?
  5. I

    B Electromagnetic waves/radiation properties?

    As I understand it, light is an electromagnetic wave consisting of an oscillating electric and magnetic fields perpendicular to each other. Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to...
  6. I

    Redshift, Earth's orbital speed, and the speed of light

    The Earth is moving around the Sun at around 30km/s, a change of 60km/s over the course of the year. Presumably, measurements of the speed of light would show a redshift up to ±30km/s? Are redshift measurements this accurate? Likewise, the speed of the Solar System around the Milky Way, is...
  7. I

    Laws, principles and facts

    Although scientists once thought that radioactivity violated the law of conservation of energy, then new understanding of nuclear decay helped demonstrate that the law was fact. So why do we continue to call the Conservation of Energy a law, and not a fact. Why not a principle? Is there a...
  8. I

    Is fire a plasma?

    I think that most people would describe a lightning bolt as a plasma because of the ionised air it produces. There are several parameters that may define a plasma. Interestingly, a gas may be ionized to only a fraction of a percent, and fulful the requirements that define it as a plasma:
  9. I

    Is fire a plasma?

    It is not as clear cut as that. Fire may be a plasma. See"
  10. I

    Plasma types

    Plasmas are usually "typed", or classified, in other ways. For example: Cold, warm and hot plasmas Fully/partially ionized plasma Collisional/Non-collisional plasma Neutral/Non-neutral plasma High/medium/low density plasma Magnetic /Non-magnetic plasma Dusty/grain plasmas...
  11. I

    Plasma types

    A plasma is generally described as a collection of charged particles, but the species of ions does make for different kinds of plasma. More usually, the (positive) ions are mixed with equal numbers of negative ions: electrons. Ionizing any element will produce its corresponding plasma. So yes, a...
  12. I

    Is fire a plasma?

    Have a look at some of the links at the beginning of this thread. In summary, fire is sometimes a plasma, and sometimes not. It all depends on your definitions, and how you define a plasma.
  13. I

    Quick Plasma Question

    It depends on the plasma. A candle flame, a very weak plasma, requires nothing to "contain it". A bolt of lightning is self-contained by its own electromagnetic pinch. The plasma in a neon sign is contained by glass (though it forms a sheath parallel to the glass surface). And the plasma in...
  14. I

    Is Dark Matter a solid, gas or liquid?

    I don't think that's quite right, because "cold plasma" and "hot plasma" have special meanings in plasma physics. For example, the plasma created in a fluorescent light tube is defined as a cold plasma, yet it emits light.(Ref) Conversely, the Solar Wind is classed as a hot plasma, but as far...
  15. I

    Plasma cosmology

    I would argue that the approach is irrelevant, a citation stands by itself. As an example, Ivan Seeking has noted that "Wiki is not a credible scientific reference. However, it is allowed within a context that is already well understood"(post). Two examples: So if there is a general...