jeheron

I recently attended a popular science lecture at the University of Sydney. The speaker said that if, given enough time, you travelled in a straight line out into space, you would eventually arrive back where you started from as if space was circular and you had circumnavigated it. Is this remotely correct?

Two parallel wires are separated by a distance of 6 cm. Wire 1, on the left, carries current into the page. An equal current flows in wire 2 out of the page. What direction is the net magnetic field at point A, half between the wires? In our Physics course we are given the equation F=Eq, and Ed=V. I have tried for 20 minutres using the information we have been given to work out the answer. How do you do this question?

How do NPN and PNP transistors work. I understand n-type materials and p-type materials as well as the workings of a p-n junction in terms of doping and electrons and electron holes working as charge carriers. Jack

In terms of the proerties of the materials themselves. I am asking the question to better understand each individual kind of semiconductor matieral before moving onto p-n junctions and npn and pnp interfaces.

Is there any observable difference between the physical and electrical properties of n-type semiconductor materials and p-type semiconductor materials?

How does the behaviour of semiconductors vary with different densities of electrons or electron holes?

In terms of semiconductors, and electrons moving from the valence to conduction bands, how do the remaining electron holes contribute to electrical conductivity? Also, can anyone provide a short qualitative description of the properties of an electron hole as I am not totally familiar with the concept?

1) I am completing my last year of secondary school in Australia, and energy bands are included in the course syllabus. This however is not my only motivation for asking the question I have. My passion is for physics, and to me, this is very interesting. 2) I have read a lot of superficial material that discusses QM, but nothing to deep. So my knowledge is limited. I am always looking to learn more though. In regards to this topic, I have read into the Pauli exclusion principle, and energy levels, in an attempt to understand energy bands.

In what materials/states of matter do energy bands form? What determines whether an energy band will exist? For example, do energy bands ever form in gases? Cheers!

I have recently started studying the photoelectric effect. I currently have very little understanding of the theory. As i understand it retarding voltage is a voltage applied to the anode and the cathode of a photovoltaic cell such that any photoelectrons emitted are decelerated just enough such that they don’t reach the anode. This is a very superficial understanding, and could be totally wrong. Can anyone help me qualitatively refine my understanding? Also, why is a retarding voltage ever used? Jack.

Ok, so in a crystalline substance there are billions of atoms and molecules. Their energy levels, due to the Pauli exclusion principle, cannot all have the same value, as a result they each vary slightly. This creates bands of electron (or moledule?) energy. Is that right?

What is the difference between an energy band and an energy level (how, if at all, are they related)? (In summary) my current understanding is that an energy level is "any of the possible discrete energies of an atom, molecule, or nucleus." and that energy bands have something to do with semiconductors. Hopefully very soon my understand will be much greater.

I am a high school student in Australia, we briefly discussed Maxwell’s equations in class however what you have said here does not helpfully answer my question (from me at least). It seems to me as unhelpful as saying that the fundamental quality of the universe that causes gravity is an equation Newton published in 1679. I would like to believe Maxwell’s equations, rather than being the fundamental origin of electromagnetic radiation, merely (although amazingly elegantly) describe this radiation. The words "accelerating charges" however begin spark thought in my mind. An accelerating charge induces a magnetic field, which in turn induces an electric field, ad infinitum. Is this perhaps the origin of EM radiation (although not the fundamental origin of course)? Thank you very much Klaynos, for your reply, Jack

What is the fundamental origin of electromagnetic radiation?

Thanks for your help. I just found the source the question was taken from. In the copy of the question we were given the photocopier had cut off "The plates are 0.1m lin length." That changes the method of calculation, making it alot easier. Thanks again.